COLOR-CODE STANDARDS FOR NETWORK CABLE

Again, please bear with me...  Let's start with simple pin-out diagrams of the two types of UTP Ethernet cables and watch how committees can

make a can of worms out of them.  Here are the diagrams:

Note that the TX (transmitter) pins are connected to corresponding RX (receiver) pins, plus to plus and minus to minus.  And that  you must use a crossover cable to connect units with identical interfaces.  If you use a straight-through cable, one of the two units must, in effect, perform the cross-over function.

Two wire color-code standards apply: EIA/TIA 568A and EIA/TIA 568B. The codes are commonly depicted with RJ-45 jacks as follows (the view is from the front of the jacks):

If we apply the 568A color code and show all eight wires, our pin-out looks like this:

Note that pins 4, 5, 7, and 8 and the blue and brown pairs are not used in either standard.  Quite contrary to what you may read elsewhere, these pins and wires are not used or required to implement 100BASE-TX duplexing--they are just plain wasted.

However, the actual cables are not physically that simple.  In the diagrams, the orange pair of wires are not adjacent.  The blue pair is upside-down.  The right ends match RJ-45 jacks and the left ends do not.  If, for example, we invert the left side of the 568A "straight"-thru cable to match a 568A jack--put one 180° twist in the entire cable from end-to-end--and twist together and rearrange the appropriate pairs, we get the following can-of-worms:

This further emphasizes, I hope,  the importance of the word "twist" in making network cables which will work.  You cannot use an flat-untwisted telephone cable for a network cable.  Furthermore, you must use a pair of twisted wires to connect a set of transmitter pins to their corresponding receiver pins.  You cannot use a wire from one pair and another wire from a different pair.

Keeping the above principles in mind, we can simplify the diagram for a 568A straight-thru cable by untwisting  the wires, except the 180° twist in the entire cable, and bending the ends upward.  Likewise, if we exchange the green and orange pairs in the 568A diagram we will get a simplified diagram for a 568B straight-thru cable.  If we cross the green and orange pairs in the 568A diagram we will arrive at a simplified diagram for a crossover cable.  All three are shown below.

HOW TO MAKE YOUR OWN CAT 5 TWISTED-PAIR NETWORK CABLESLast updated: 1/18/2001

INTRODUCTION.  The purpose of this article is to show you how to make the two kinds of cables which can be used to network two or more computers together to form quick and simple home or small office local area networks (LANs).  These instructions can also be used to make patch cables for networks with more complex infrastructure wiring.

The two most common unshielded twisted-pair (UTP) network standards are the10 Mhz 10BASE-T Ethernet and the 100Mhz 100BASE-TX Fast Ethernet.  The 100BASE-TX standard is quickly becoming the predominant LAN standard.  If you are starting from scratch, to build a small home or office network, this is clearly the standard you should choose.  This article will show you how to make cables which will work with both standards.

LANS SIMPLIFIED.  A LAN can be as simple as two computers, each having a network interface card (NIC) or network adapter and running network software, connected together with a crossover cable. 

The next step up would be a network consisting of three or more computers and a hub.  Each of the computers is plugged into the hub with a straight-thru cable (the crossover function is performed by the hub).

Registered jack (R J – 45)

A registered jack (RJ) is a standardized physical network interface — both jack construction and wiring

pattern — for connecting telecommunications or data equipment to a service provided by a local

exchange carrier or long distance carrier. The standard designs for these connectors and their wiring are

named RJ11, RJ14,RJ21, RJ48, etc. Many of these interface standards are commonly used in North

America, though some interfaces are used world-wide.

The physical connectors that registered jacks use are mainly of the modular connectorand 50-

pin miniature ribbon connector types. For example, RJ11 uses a 6 position 4 conductor (6P4C) modular

plug and jack, while RJ21 uses a 50-pin miniature ribbon connector.

Left to right, RJ connectors:

an eight-contact 8P8C plug (used for RJ49, RJ61 and others, but often called "RJ45" because of its outward

semblance to the true RJ45)

six-contact RJ25 plug

four-contact RJ14 plug (often also used instead of two-pin RJ11)

a four-contact handset plug (also popularly, though incorrectly, called "RJ22", "RJ10", or "RJ9")

RJ25 and RJ14 can be plugged into the same standard six-pin jack, pictured.

Naming confusion

Strictly, "registered jack" refers to both the female physical connector (modular connector) and its wiring,

but the term is often used loosely to refer to modular connectors regardless of wiring, such as in Ethernet

over twisted pair.

There is much confusion over these connection standards. The six-position plug and jack commonly used

for telephone line connections may be used for RJ11, RJ14 or even RJ25, all of which are actually names

of interface standards that use this physical connector. The RJ11 standard dictates a 2-wire connection,

while RJ14 uses a 4-wire configuration, and RJ25 uses all six wires. The RJ abbreviations, though, only

pertain to the wiring of the jack (hence the name "registered jack"); it is commonplace but not strictly

correct to refer to an unwired plug connector by any of these names.

Plugs and jacks of this type are often called modular connectors, which originally distinguished them from

older telephone connectors, which were very bulky or wired directly to the wall and therefore not

accommodating of modular systems. A common nomenclature for modular connectors is e.g. "6P" to

indicate a six-position modular plug or jack. Sometimes the nomenclature is expanded to indicate the

number of positions that contain conductors. For example, a six-position modular plug with conductors in

the middle two positions and the other four positions unused is called a 6P2C. RJ11 uses a 6P plug;

furthermore, it often uses a 6P2C. (The connectors could be supplied more pins, but if more pins are

actually wired, the interface is no longer an RJ11.)

Registered jacks were created by the FCC to be the standard interface between a telephone company

and a customer. The wired communications provider (telephone company) is responsible for delivery of

services to a minimum point of entry (MPOE) (physically a utility box) which connects the

telephone/network wiring on the customer's property (CPE - Customer-premises equipment) to the

communication provider's network. The customer is responsible for jacks, wiring, and equipment on their

side of the MPOE. The intent is to establish a universal standard for wiring and interfaces, and to

separate ownership of in-home (or in-office) telephone wiring away from (North America's)Bell

Systems and relinquish ownership of wiring in an entity's owned structure to that entity.

The various interfaces created due to this regulation were numbered and integrated into the

telecommunications' order system by adopting them as Universal Service Order Codes (USOC). USOCs

are commonly passed to the communications provider by large businesses for a variety of services.

Because there are many standardized interface options available to the customer, the customer must

specify the type of interface required, by RJ/USOC. And for a multi-line interface such as the RJ21, they

must denote which position(s) of the interface are to be used. If there are multiple RJ21 connectors, they

are numbered sequentially and the customer must advise the communications provider of which one to

use.

Twisted pair

See also: Category 5 cable and TIA/EIA-568-B

While the plugs are generally used with a flat cable (a notable exception being Ethernet twisted-pair

cabling used with the 8P8C modular plug), the long cables feeding them in the building wiring and the

phone network before them are normally twisted pair. Wiring conventions were designed to take full

advantage of the physical compatibility ensuring that using a smaller plug in a larger socket would pick up

complete pairs not a (relatively useless) two half pairs but here again there has been a problem. The

original concept was that the centre two pins would be one pair, the next two out the second pair, and so

on until the outer pins of an eight-pin connector would be the fourth twisted pair. Additionally, signal

shielding was optimised by alternating the “live” (hot) and “earthy” (ground) pins of each pair. This

standard for the eight-pin connector is the USOC-defined pinout, but the outermost pair are then too far

apart to meet the electrical requirements of high-speed LAN protocols. Two variations known

as T568A and T568B overcome this by using adjacent pairs of the outer four pins for the third and fourth

pairs. For T568A, the inner four pins are wired identically to those in RJ14. In the T568B variant, different

pairs are assigned to different pins, so a T568B jack is incompatible with the wiring pattern of RJ14. In

connecting cables, however, the performance differences between the pairs that are assigned to different

pins are minimal, and in general use T568A and T568B patch cables are interchangeable.

History and authority

For more details on this topic, see Interconnection.

Under the Bell System monopoly (following the Communications Act of 1934), the Bell System owned the

phones and did not allowinterconnection of separate phones or other terminal equipment; a popular

saying was "Ma Bell has you by the calls". Phones were generally hardwired, or at times used proprietary

Bell System connectors.

This began to change with the case Hush-A-Phone v. United States [1956] and

the FCC's Carterfone [1968] decision, which required Bell to allow some interconnection, which

culminated in registered jacks.

Registered jacks were introduced by the Bell System in the 1970s under a 1976 FCC order ending the

use of protective couplers. They replaced earlier, bulkier connectors. The Bell System issued

specifications for the modular connectors and their wiring as Universal Service Ordering Codes (USOC),

which were the only standard at the time.

When the US telephone industry was opened to more competition in the 1980s, the specifications were

made a matter of US law, ordered by the Federal Communications Commission (FCC) and codified in the

Code of Federal Regulations, 47 CFR 68, subpart F.

In January 2001, the FCC turned over responsibility for standardizing connections to the telephone

network to a new private industry organization, the Administrative Council for Terminal Attachment

(ACTA). The FCC removed Subpart F from the CFR and added Subpart G, which delegates the task to

the ACTA. The ACTA published a standard called TIA/EIA-IS-968 which contained the information that

was formerly in the CFR. The current version of that standard, called TIA-968-A, specifies the modular

connectors at length, but not the wiring. Instead, TIA-968-A incorporates a standard called T1.TR5-1999

by reference to specify the wiring. Note that a registered jack name such as RJ11 identifies both the

physical connectors and the wiring (pinout) of it (see above).

International use

The modular jack was chosen as a candidate for ISDN systems. In order to be considered, the connector

system had to be defined under international standards. In turn this led to ISO 8877. Under the rules of

the IEEE 802 standards project, international standards are to be preferred over national standards so the

modular connector was chosen for IEEE 802.3i-1990, the original 10BASE-T twisted-pair wiring version

of Ethernet.

Registered jack types

It has been suggested that RJ11, RJ14, RJ25, RJ21, RJ48 and RJ61 be merged into this article or section. (Discuss)

It has been suggested that this section be split into a new article titled List of registered jacks. (Discuss)

The most familiar registered jack is probably the RJ11. This is a 6 position modular connector wired for

one phone line, and is found in most homes and offices in North America for single line telephones.

RJ14 and RJ25 are also fairly common, using the same size connector as RJ11, but with two and three

phone lines, respectively, connected.

Essentially all one, two, and three line analog telephones made today (2009) are meant to plug into RJ11,

RJ14, or RJ25 jacks, respectively.

The true RJ45(S) is an extremely uncommon registered jack, but the name "RJ45" is also used quite

commonly to refer to any 8P8C modular connector.

Many of the basic names have suffixes that indicate subtypes:

C: flush-mount or surface mount

W: wall-mount

S: single-line

M: multi-line

X: complex jack

For example, RJ11 comes in two forms: RJ11W is a jack from which you can hang a wall telephone, while

RJ11C is a jack designed to have a cord plugged into it. (You can plug a cord into an RJ11W as well, but

it usually doesn't look as nice as a cord plugged into an RJ11C.)

RJ2MB: 50-pin miniature ribbon connector, 2-12 telephone lines with make-busy

RJ11 C/RJ11W: 6P2C, for one telephone line (6P4C with power on second pair)

RJ12 C/RJ12W: 6P6C, for one telephone line ahead of the key system (key telephone system)

RJ13C/RJ13W: 6P4C, for one telephone line behind the key system (key telephone system)

RJ14 C/RJ14W: 6P4C, for two telephone lines (6P6C with power on third pair)

RJ15C: 3-pin weatherproof, for one telephone line

RJ18C/RJ18W : 6P6C, for one telephone line with make-busy arrangement

RJ21 X: 50-pin miniature ribbon connector, for up to 25 lines

RJ25 C/RJ25W: 6P6C, for three telephone lines

RJ26X: 50-pin miniature ribbon connector, for multiple data lines, universal

RJ27X: 50-pin miniature ribbon connector, for multiple data lines, programmed

RJ31 X: 8P8C (although usually only 4C are used), Often incorrectly stated as allowing alarm (fire

and intrusion) equipment to seize a phone line, the jack is actually used to disconnect the equipment

from the phone line while allowing the phone circuit to continue to the site phones.

RJ38X: 8P8C, similar to RJ31X, with continuity circuit

RJ41S: 8P8C keyed, for one data line, universal

RJ45S: 8P2C + keyed, for one data line with programming resistor

RJ48 S: 8P8C, for four-wire data line (DDS)

RJ48C: 8P8C, for four-wire data line (DSX-1)

RJ48X: 8P8C with shorting bar, for four-wire data line (DS1)

RJ49C: 8P8C, for ISDN BRI via NT1

RJ61 X: 8P8C, for four telephone lines

RJ71C: 12 line series connection using 50 pin connector (with bridging adapter) ahead of

customer equipment. Mostly used for call sequencer equipment.

"Unofficial" (incorrect) plug names

These "RJ" names do not really refer to truly existing ACTA RJ types:

"RJ9", "RJ10", "RJ22": 4P4C or 4P2C, for telephone handsets. Since telephone handsets do not

connect directly to the public network, they have no registered jack code whatsoever.

"RJ45": 8P8C, informal designation for T568A/T568B, including Ethernet; not the same as the

true RJ45/RJ45S

"RJ50": 10P10C, for data

RJ -45

RJ45 pin numberingBefore we start with the discussion of wiring schemes for modular jacks, it is good to know how pins are numbered on RJ45 and other modular jacks. The following scheme shows the exact pin numbering on both male and female RJ45 connectors.

RJ45 pin numbering

All other modular jacks—like RJ11—start counting at the same side of the connector. In the wiring diagrams with modular jacks on this site we prefer to use a picture of the jack upside down, with the hook underneath.

The straight through RJ45 network cable, EIA/TIA 568B

The most common wiring for RJ45 cables is the straight through cable. In this cable layout, all pins are wired one-to-one to the other side. The pins on the RJ45 connector are assigned in pairs, and every pair carries one differential signal. Each line pair has to be twisted. If UTP or FTP cable is used, the pairs have orange, brown, blue and green colors. The wiring of these cables to RJ45 to make a straight through cable is defined by EIA/TIA 568B. The RJ45 connectors on both ends are wired in the same way. The color scheme is shown below.

Straight through RJ45 color coding - EIA/TIA 568B

The cross over RJ45 network cable, EIA/TIA 568A

The straight through RJ45 cable is commonly used to connect network cards with hubs on 10Base-T and 100Base-Txnetworks. On network cards, pair 1-2 is the transmitter, and pair 3-6 is the receiver. The other two pairs are not used. On hubs pair 1-2 is the receiver and 3-6 the transmitter. Because of this a straight through RJ45 cable can be used to connect network cards to hubs.

In very small network configurations where only two computers have to be connected, the use of a hub is not necessary. The straight through RJ45 cable cannot be used in that situation. Also when two hubs have to be connected to increase the number of nodes on a

network segment, this cable is not appropriate. In both situations a cross over RJ45 cable is necessary, where the transmit and receive lines on both RJ45 connectors are cross connected. The color coding for the cross over RJ45 cable has been defined in the EIA/TIA 568A standard.

Please note: One   RJ45   connector has to be wired as   EIA / TIA   568B , the other as   EIA / TIA   568A . When wiring both ends as EIA/TIA 568A, the resulting cable is a straight through cable again.

Cross over RJ45 color coding - EIA/TIA 568A

Common data and voice wiring schemes

Depending of the situation where modular cables are used, the wiring schemes with modular jacks differ. The most common wiring schemes can be seen in the picture below.

Common modular jack wiring schemes

Female connector, looking from the open end

Introduction

A computer network allows computers to communicate with many other computers and to share

resources and information. The Advanced Research Projects Agency (ARPA) funded the design of the

"Advanced Research Projects Agency Network" (ARPANET) for the United States Department of

Defense. It was the first operational computer network in the world.[1] Development of the network began

in 1969, based on designs developed during the 1960s.

Network classification

What is networking? The following list presents categories used for classifying networks. In the world of

computers, networking is the practice of linking two or more computing devices together for the purpose

of sharing data. Networks are built with a mix of computer hardware and computer software

Connection method

What is Networking? In the world of computers, networking is the practice of linking two or more

computing devices together for the purpose of sharing data. Networks are built with a mix of computer

hardware and computer software. Computer networks can also be classified according to the hardware

and software technology that is used to interconnect the individual devices in the network, such as Optical

fiber, Ethernet,Wireless LAN, HomePNA, Power line communication or G.hn. Ethernet uses physical

wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers.

Wireless LAN technology is designed to connect devices without wiring. These devices useradio

waves or infrared signals as a transmission medium.

ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a

high-speed (up to 1 Gigabit/s) local area network.

Wired Technologies

Twisted-Pair Wire - This is the most widely used medium for telecommunication. Twisted-pair wires are

ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for

both voice and data transmission. The use of two wires twisted together helps to

reduce crosstalk and electromagnetic induction. The transmission speed range from 2 million bits per

second to 100 million bits per second.

Coaxial Cable – These cables are widely used for cable television systems, office buildings, and other

worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating

layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a

conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed

range from 200 million to more than 500 million bits per second.

Fiber Optics – These cables consist of one or more thin filaments of glass fiber wrapped in a protective

layer. It transmits light which can travel over long distance and higher bandwidths. Fiber-optic cables are

not affected by electromagnetic radiation. Transmission speed could go up to as high as trillions of bits

per second. The speed of fiber optics is hundreds of times faster than coaxial cables and thousands of

times faster than twisted-pair wire.

Wireless Technologies

Terrestrial Microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment

look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all

communications to line-of-sight. Path between relay stations spaced approx. 30 miles apart. Microwave

antennas are usually placed on top of buildings, towers, hills, and mountain peaks.

Communications Satellites – The satellites use microwave radio as their telecommunications medium

which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000

miles above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data,

and TV signals.

Cellular and PCS Systems – Use several radio communications technologies. The systems are divided to

different geographic area. Each area has low-power transmitter or radio relay antenna device to relay

calls from one area to the next area.

Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital

cellular and a low-frequency radio technology. Wireless LANS use spread spectrum technology to enable

communication between multiple devices in a limited area. Example of open-standard wireless radio-

wave technology is IEEE 802.11b.

Bluetooth – A short range wireless technology. Operate at approx. 1Mbps with range from 10 to 100

meters. Bluetooth is an open wireless protocol for data exchange over short distances.

The Wireless Web – The wireless web refers to the use of the World Wide Web through equipments like

cellular phones, pagers,PDAs, and other portable communications devices. The wireless web service

offers anytime/anywhere connection.

Scale

Networks are often classified as Local Area Network (LAN), Wide Area Network (WAN), Metropolitan

Area Network (MAN), Personal Area Network (PAN), Virtual Private Network (VPN), Campus Area

Network (CAN), Storage Area Network (SAN), etc. depending on their scale, scope and purpose. Usage,

trust levels and access rights often differ between these types of network - for example, LANs tend to be

designed for internal use by an organization's internal systems and employees in individual physical

locations (such as a building), while WANs may connect physically separate parts of an organization to

each other and may include connections to third parties.

Functional relationship (network architecture)

Computer networks may be classified according to the functional relationships which exist among the

elements of the network, e.g., Active Networking, Client-server and Peer-to-peer (workgroup)

architecture.

Network topology

Computer networks may be classified according to the network topology upon which the network is

based, such as bus network, star network,ring network, mesh network, star-bus network, tree or

hierarchical topology network. Network topology signifies the way in which devices in the network see

their logical relations to one another. The use of the term "logical" here is significant. That is, network

topology is independent of the "physical" layout of the network. Even if networked computers are

physically placed in a linear arrangement, if they are connected via a hub, the network has a Star

topology, rather than a bus topology. In this regard the visual and operational characteristics of a network

are distinct; the logical network topology is not necessarily the same as the physical layout. Networks may

be classified based on the method of data used to convey the data, these include digital and analog

networks.

Types of networks

Below is a list of the most common types of computer networks in order of scale.

Personal area network

A personal area network (PAN) is a computer network used for communication among computer devices

close to one person. Some examples of devices that are used in a PAN are personal computers, printers,

fax machines, telephones, PDAs, scanners, and even video game consoles. Such a PAN may include

wired and wireless connections between devices. The reach of a PAN is typically at least about 20-30 feet

(approximately 6-9 meters), but this is expected to increase with technology improvements.

Local area network

A local Area Network (LAN) is a computer network covering a small physical area, like a home, office, or

small group of buildings, such as a school, or an airport. Current wired LANs are most likely to be based

on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired

LAN using existing home wires (coaxial cables, phone lines and power lines)[2].

For example, a library may have a wired or wireless LAN for users to interconnect local devices (e.g.,

printers and servers) and to connect to the internet. On a wired LAN, PCs in the library are typically

connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of

interconnected devices and eventually connect to the Internet. The cables to the servers are typically on

Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbit/s. A wireless LAN may exist using a

different IEEE protocol, 802.11b, 802.11g or possibly 802.11n. The staff computers (bright green in the

figure) can get to the color printer, checkout records, and the academic network and the Internet. All user

computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note

that the printers are not accessible from outside their workgroup.

Typical library network, in a branching tree topology and controlled access to resources

All interconnected devices must understand the network layer (layer 3), because they are handling

multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet

connections to the user device and a Gigabit Ethernet connection to the central router, could be called

"layer 3 switches" because they only have Ethernet interfaces and must understand IP. It would be more

correct to call them access routers, where the router at the top is a distribution router that connects to the

Internet and academic networks' customer access routers.

The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data

transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current

Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data

transfer rate. IEEE has projects investigating the standardization of 40 and 100 Gbit/s.[3]

Campus area network

A campus area network (CAN) is a computer network made up of an interconnection of local area

networks (LANs) within a limited geographical area. It can be considered one form of a metropolitan area

network, specific to an academic setting.

In the case of a university campus-based campus area network, the network is likely to link a variety of

campus buildings including; academic departments, the university library and student residence halls. A

campus area network is larger than a local area network but smaller than a wide area network (WAN) (in

some cases).

The main aim of a campus area network is to facilitate students accessing internet and university

resources. This is a network that connects two or more LANs but that is limited to a specific and

contiguous geographical area such as a college campus, industrial complex, office building, or a military

base. A CAN may be considered a type of MAN (metropolitan area network), but is generally limited to a

smaller area than a typical MAN. This term is most often used to discuss the implementation of networks

for a contiguous area. This should not be confused with a Controller Area Network. A LAN connects

network devices over a relatively short distance. A networked office building, school, or home usually

contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per

room), and occasionally a LAN will span a group of nearby buildings.

Metropolitan area network

A metropolitan area network (MAN) is a network that connects two or more local area networks or

campus area networks together but does not extend beyond the boundaries of the immediate town/city.

Routers, switches and hubs are connected to create a metropolitan area network.

Wide area network

A wide area network (WAN) is a computer network that covers a broad area (i.e. any network whose

communications links cross metropolitan, regional, or national boundaries [1]). Less formally, a WAN is a

network that uses routers and public communications links. Contrast with personal area networks (PANs),

local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs), which

are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. The

largest and most well-known example of a WAN is the Internet. A WAN is a data communications network

that covers a relatively broad geographic area (i.e. one city to another and one country to another

country) and that often uses transmission facilities provided by common carriers, such as telephone

companies. WAN technologies generally function at the lower three layers of the OSI model|OSI

reference model: the physical layer, the data link layer, and the network layer.

Global area network

A global area networks (GAN) (see also IEEE 802.20) specification is in development by several groups,

and there is no common definition. In general, however, a GAN is a model for supporting mobile

communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key

challenge in mobile communications is "handing off" the user communications from one local coverage

area to the next. In IEEE Project 802, this involves a succession of terrestrial WIRELESS local area

networks (WLAN).[4]

Virtual private network

A virtual private network (VPN) is a computer network in which some of the links between nodes are

carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by

physical wires. The data link layer protocols of the virtual network are said to be tunneled through the

larger network when this is the case. One common application is secure communications through the

public Internet, but a VPN need not have explicit security features, such as authentication or content

encryption. VPNs, for example, can be used to separate the traffic of different user communities over an

underlying network with strong security features.

A VPN may have best-effort performance, or may have a defined service level agreement (SLA) between

the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than

point-to-point.

A VPN allows computer users to appear to be editing from an IP address location other than the one

which connects the actual computer to the Internet.

Internetwork

An Internetwork is the connection of two or more distinct computer networks or network segments via a

common routing technology. The result is called an internetwork (often shortened to internet). Two or

more networks or network segments connect using devices that operate at layer 3 (the 'network' layer) of

the OSI Basic Reference Model, such as a router. Any interconnection among or between public, private,

commercial, industrial, or governmental networks may also be defined as an internetwork.

In modern practice, interconnected networks use the Internet Protocol. There are at least three variants of

internetworks, depending on who administers and who participates in them:

Intranet

Extranet

Internet

Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the

intranet or extranet is normally protected from being accessed from the Internet without proper

authorization. The Internet is not considered to be a part of the intranet or extranet, although it may serve

as a portal for access to portions of an extranet.

Intranet

An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and

file transfer applications, that is under the control of a single administrative entity. That administrative

entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal

network of an organization. A large intranet will typically have at least one web server to provide users

with organizational information.

Extranet

An extranet is a network or internetwork that is limited in scope to a single organization or entity and also

has limited connections to the networks of one or more other usually, but not necessarily, trusted

organizations or entities (e.g., a company's customers may be given access to some part of its intranet

creating in this way an extranet, while at the same time the customers may not be considered 'trusted'

from a security standpoint). Technically, an extranet may also be categorized as a CAN, MAN, WAN, or

other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at

least one connection with an external network.

Internet

The Internet consists of a worldwide interconnection of governmental, academic, public, and private

networks based upon the networking technologies of the Internet Protocol Suite. It is the successor of

the Advanced Research Projects Agency Network (ARPANET) developed byDARPA of the U.S.

Department of Defense. The Internet is also the communications backbone underlying the World Wide

Web (WWW). The 'Internet' is most commonly spelled with a capital 'I' as a proper noun, for historical

reasons and to distinguish it from other generic internetworks.

Participants in the Internet use a diverse array of methods of several hundred documented, and often

standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP

Addresses) administered by the Internet Assigned Numbers Authority and address registries. Service

providers and large enterprises exchange information about the reachability of their address spaces

through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

Basic hardware components

All networks are made up of basic hardware building blocks to interconnect network nodes, such as

Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of

connecting these building blocks is required, usually in the form of galvanic cable (most

commonly Category 5 cable). Less common are microwave links (as in IEEE 802.12) or optical cable

("optical fiber"). An Ethernet card may also be required.

Network interface cards

A network card, network adapter, or NIC (network interface card) is a piece of computer

hardware designed to allow computers to communicate over a computer network. It provides physical

access to a networking medium and often provides a low-level addressing system through the use

of MAC addresses.

Repeaters

A repeater is an electronic device that receives a signal and retransmits it at a higher power level, or to

the other side of an obstruction, so that the signal can cover longer distances without degradation. In

most twisted pair Ethernet configurations, repeaters are required for cable which runs longer than 100

meters.

Hubs

A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all

ports of the hub for transmission. The destination address in the frame is not changed to a broadcast

address.[5]

Bridges

A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model.

Bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are

reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for

that address only to that port. Bridges do send broadcasts to all ports except the one on which the

broadcast was received.

Bridges learn the association of ports and addresses by examining the source address of frames that it

sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge

assumes that MAC address is associated with that port. The first time that a previously unknown

destination address is seen, the bridge will forward the frame to all ports other than the one on which the

frame arrived.

Bridges come in three basic types:

1. Local bridges: Directly connect local area networks (LANs)

2. Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote

bridges, where the connecting link is slower than the end networks, largely have been replaced

with routers.

3. Wireless bridges: Can be used to join LANs or connect remote stations to LANs

Switches

A network switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data

communication) between ports (connected cables) based on the MAC addresses in the packets.[6] This is

distinct from a hub in that it only forwards the packets to the ports involved in the communications rather

than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address

(OSI Layer 3) which is necessary for communicating between network segments or within a large or

complex LAN. Some switches are capable of routing based on IP addresses but are still called switches

as a marketing term. A switch normally has numerous ports, with the intention being that most or all of the

network is connected directly to the switch, or another switch that is in turn connected to a switch.[7]

Switch is a marketing term that encompasses routers and bridges, as well as devices that may distribute

traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or

more OSI model layers, including physical, data link, network, or transport (i.e., end-to-end). A device that

operates simultaneously at more than one of these layers is called a multilayer switch.

Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand

networking. Many experienced network designers and operators recommend starting with the logic of

devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device

selection is an advanced topic that may lead to selecting particular implementations, but multilayer

switching is simply not a real-world design concept.

Routers

A router is a networking device that forwards packets between networks using information in protocol

headers and forwarding tables to determine the best next router for each packet. Routers work at

the Network Layer (layer 3) of the OSI model and the Internet Layer of TCP/IP.

Wireless access point

In computer networking, a wireless access point (WAP) is a device that allows wireless communication

devices to connect to a wireless network using Wi-Fi, Bluetooth or related standards. The WAP usually

connects to a wired network, and can relay data between the wireless devices (such as computers or

printers) and wired devices on the network.

In industrial wireless networking, the design is rugged with a metal cover, a Din-Rail mount, and a

wider temperature range during operations, high humidity and exposure to water, dust, and oil. Wireless

security includes: WPA-PSK, WPA2, IEEE 802.1x/RADIUS, WDS, WEP, TKIP,

and CCMP (AES) encryption.

Unlike home consumer models, industrial wireless access points can also be used as a bridge, router, or

a client.

Planet WsAP-4000 Wireless Access Point

Introduction

Linksys WAP54G 802.11g Wireless Access Point

embedded RouterBoard 112 withU.FL-RSMA pigtail and R52 mini PCI Wi-Fi  card widely used by wireless Internet  service

providers (WISPs) across the world

Prior to wireless networks, setting up a computer network in a business, home, or school often required

running many cables through walls and ceilings in order to deliver network access to all of the network-

enabled devices in the building. With the advent of the Wireless Access Point, network users are now

able to add devices that access the network with few or no cables. Today's WAPs are built to support a

standard for sending and receiving data using radio frequencies rather than cabling. Those standards,

and the frequencies they use are defined by the IEEE. Most WAPs use IEEE 802.11 standards.

Common WAP Applications

A typical corporate use involves attaching several WAPs to a wired network and then providing wireless

access to the office LAN. The wireless access points are managed by a WLAN Controller which handles

automatic adjustments to RF power, channels, authentication, and security. Further, controllers can be

combined to form a wireless mobility group to allow inter-controller roaming. The controllers can be part of

a mobility domain to allow clients access throughout large or regional office locations. This saves the

clients time and administrators overhead because it can automatically re-associate or re-authenticate.

Further, multiple controllers and all of the hundreds of access points attached to those controllers can be

managed by a software called Cisco Wireless Control System Which handles the same functions as a

controller yet adds the bonus features of mapping user or RFID locations to an uploaded map, upgrading

controllers and access point firmware, and rogue detection/handling. In this instance, the WAP functions

as a gateway for clients to access the wired network.

A Hot Spot is a common public application of WAPs, where wireless clients can connect to the Internet

without regard for the particular networks to which they have attached for the moment. The concept has

become common in large cities, where a combination of coffeehouses, libraries, as well as privately

owned open access points, allow clients to stay more or less continuously connected to the Internet, while

moving around. A collection of connected Hot Spots can be referred to as a lily-pad network.

The majority of WAPs are used in Home wireless networks.[citation needed] Home networks generally have only

one WAP to connect all the computers in a home. Most are wireless routers, meaning converged

devices that include the WAP, a router, and, often, an ethernet switch. Many also include a broadband

modem. In places where most homes have their own WAP within range of the neighbors' WAP, it's

possible for technically savvy people to turn off their encryption and set up a wireless community network,

creating an intra-city communication network without the need of wired networks.

A WAP may also act as the network's arbitrator, negotiating when each nearby client device can transmit.

However, the vast majority of currently installed IEEE 802.11 networks do not implement this, using a

distributed pseudo-random algorithm called CSMA/CA instead.

Wireless Access Point vs. Ad-Hoc Network

Some people confuse Wireless Access Points with Wireless Ad-Hoc networks. An Ad-Hoc network uses a

connection between two or more devices without using an access point: the devices communicate

directly. An Ad-Hoc network is used in situations such as a quick data exchange or a multiplayer LAN

game because it is easy to set up and does not require an access point. Due to its peer-to-peer layout,

Ad-Hoc connections are similar to Bluetooth ones and are generally not recommended for a permanent

installation.

Internet access via Ad-Hoc networks, using features like Windows' Internet Connection Sharing, may

work well with a small number of devices that are close to each other, but Ad-Hoc networks don't scale

well. Internet traffic will converge to the nodes with direct internet connection, potentially congesting these

nodes. For internet-enabled nodes, Access Points have a clear advantage, being designed to handle this

load.

Limitations

One IEEE 802.11 WAP can typically communicate with 30 client systems located within a radius of

100 m.[citation needed] However, the actual range of communication can vary significantly, depending on such

variables as indoor or outdoor placement, height above ground, nearby obstructions, other electronic

devices that might actively interfere with the signal by broadcasting on the same frequency, type

of antenna, the current weather, operating radio frequency, and the power output of devices. Network

designers can extend the range of WAPs through the use of repeaters and reflectors, which can bounce

or amplify radio signals that ordinarily would go un-received. In experimental conditions, wireless

networking has operated over distances of several kilometers.[citation needed]

Most jurisdictions have only a limited number of frequencies legally available for use by wireless

networks. Usually, adjacent WAPs will use different frequencies (Channels) to communicate with their

clients in order to avoid interference between the two nearby systems. Wireless devices can "listen" for

data traffic on other frequencies, and can rapidly switch from one frequency to another to achieve better

reception. However, the limited number of frequencies becomes problematic in crowded downtown areas

with tall buildings using multiple WAPs. In such an environment, signal overlap becomes an issue causing

interference, which results in signal dropage and data errors.

Wireless networking lags behind wired networking in terms of increasing bandwidth and throughput.

While (as of 2004) typical wireless devices for the consumer market can reach speeds of 11 Mbit/s

(megabits per second) (IEEE 802.11b) or 54 Mbit/s (IEEE 802.11a, IEEE 802.11g), wired hardware of

similar cost reaches 1000 Mbit/s (Gigabit Ethernet). One impediment to increasing the speed of wireless

communications comes from Wi-Fi's use of a shared communications medium, so a WAP is only able to

use somewhat less than half the actual over-the-air rate for data throughput. Thus a typical 54 MBit/s

wireless connection actually carries TCP/IP data at 20 to 25 Mbit/s. Users of legacy wired networks

expect faster speeds, and people using wireless connections keenly want to see the wireless networks

catch up.

As of 2007 a new standard for wireless, 802.11n is awaiting final certification from IEEE. This new

standard operates at speeds up to 540 Mbit/s and at longer distances (~50 m) than 802.11g. Use of

legacy wired networks (especially in consumer applications) is expected[by whom?] to decline sharply as the

common 100 Mbit/s speed is surpassed and users no longer need to worry about running wires to attain

high bandwidth.[citation needed]

By the year 2008 draft 802.11n based access points and client devices have already taken a fair share of

the market place but with inherent problems integrating products from different vendors.

Security

Main article: Wireless LAN Security

Wireless access has special security considerations. Many wired networks base the security on physical

access control, trusting all the users on the local network, but if wireless access points are connected to

the network, anyone on the street or in the neighboring office could connect.

The most common solution is wireless traffic encryption. Modern access points come with built-in

encryption. The first generation encryption scheme WEP proved easy to crack; the second and third

generation schemes, WPA and WPA2, are considered secure if a strong

enoughpassword or passphrase is used.

Some WAPs support hotspot style authentication using RADIUS and other authentication servers.

Active networking

Active networking is a communication pattern that allows packets flowing through a telecommunications

network to dynamically modify the operation of the network.

How it works

Active network architecture is composed of execution environments (similar to a unix shell that can

execute active packets), a node operating system capable of supporting one or more execution

environments. It also consists of active hardware, capable of routing or switching as well as executing

code within active packets. This differs from the traditional network architecture which seeks robustness

and stability by attempting to remove complexity and the ability to change its fundamental operation from

underlying network components. Network processorsare one means of implementing active networking

concepts. Active networks have also been implemented as overlay networks.

What does it offer?

Active networking allows the possibility of highly tailored and rapid "real-time" changes to the underlying

network operation. This enables such ideas as sending code along with packets of information allowing

the data to change its form (code) to match the channel characteristics. The smallest program that can

generate a sequence of data can be found in the definition of Kolmogorov Complexity. The use of real-

time genetic algorithms within the network to compose network services is also enabled by active

networking.

Fundamental Challenges

Active network research addresses the nature of how best to incorporate extremely dynamic capability

within networks[1].

In order to do this, active network research must address the problem of optimally allocating computation

versus communication within communication networks[2]. A similar problem related to the compression of

code as a measure of complexity is addressed via algorithmic information theory.

Nanoscale Active Networks

As the limit in reduction of transistor size is reached with current technology, active networking concepts

are being explored as a more efficient means accomplishing computation and communication[3] [4].

BluetoothThis article is about the electronic protocol. For the medieval King of Denmark, see Harald I of Denmark.

Bluetooth logo.

Bluetooth is an open wireless protocol for exchanging data over short distances (using short length radio

waves) from fixed and mobile devices, creating personal area networks (PANs). It was originally

conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming

problems of synchronization.

Name and logo

The word Bluetooth is an anglicised version of Danish Blåtand, the epithet of the tenth-century

king Harald I of Denmark and Norway who united dissonant Danish tribes into a single kingdom. The

implication is that Bluetooth does the same with communications protocols, uniting them into one

universal standard.[1][2][3] Although blå in modern Scandinavic languages means blue, during the Viking

age it also could mean black.So a historically correct translation of Old Norse Harald Blátönn would rather

be Harald Blacktooth than Harald Bluetooth.

The Bluetooth logo is a bind rune merging the Germanic runes   (Gebo) and    (Berkanan).

[edit]Implementation

Bluetooth uses a radio technology called frequency-hopping spread spectrum, which chops up the data

being sent and transmits chunks of it on up to 79 frequencies. In its basic mode, the modulation

is Gaussian frequency-shift keying (GFSK). It can achieve a gross data rate of 1Mb/s. Bluetooth provides

a way to connect and exchange information between devices such as mobile

phones, telephones, laptops, personal computers, printers, Global Positioning System (GPS)

receivers, digital cameras, and video game consoles through a secure, globally unlicensed Industrial,

Scientific and Medical (ISM) 2.4 GHz short-range radio frequency bandwidth. The Bluetooth specifications

are developed and licensed by the Bluetooth Special Interest Group (SIG). The Bluetooth SIG consists of

companies in the areas of telecommunication, computing, networking, and consumer electronics.[4]

[edit]Uses

Bluetooth is a standard and a communications protocol primarily designed for low power consumption,

with a short range (power-class-dependent: 100m, 10m and 1m, but ranges vary in practice; see table

below) based on low-cost transceiver microchips in each device.[5]Bluetooth makes it possible for these

devices to communicate with each other when they are in range. Because the devices use a radio

(broadcast) communications system, they do not have to be in line of sight of each other.[4]

ClassMaximum Permitted

PowermW (dBm)

Range(approximate

)

Class 1 100 mW (20 dBm) ~100 metres

Class 2 2.5 mW (4 dBm) ~22 metres

Class 3 1 mW (0 dBm) ~6 metres

In most cases the effective range of class 2 devices is extended if they connect to a class 1 transceiver,

compared to a pure class 2 network. This is accomplished by the higher sensitivity and transmission

power of Class 1 devices.

VersionData Rate

Version 1.2 1 Mbit/s

Version 2.0 + EDR 3 Mbit/s

[edit]Bluetooth profiles

Main article: Bluetooth profile

In order to use Bluetooth, a device must be compatible with certain Bluetooth profiles. These define the

possible applications and uses of the technology.

[edit]List of applications

A typical Bluetooth mobile phone headset.

More prevalent applications of Bluetooth include:

Wireless control of and communication between a mobile phone and a hands-free headset. This

was one of the earliest applications to become popular.

Wireless networking between PCs in a confined space and where little bandwidth is required.

Wireless communication with PC input and output devices, the most common being

themouse, keyboard and printer.

Transfer of files, contact details, calendar appointments, and reminders between devices

with OBEX.

Replacement of traditional wired serial communications in test equipment, GPS receivers,

medical equipment, bar code scanners, and traffic control devices.

For controls where infrared was traditionally used.

For low bandwidth applications where higher [USB] bandwidth is not required and cable-free

connection desired.

Sending small advertisements from Bluetooth-enabled advertising hoardings to other,

discoverable, Bluetooth devices[6].

Wireless bridge between two Industrial Ethernet (e.g., PROFINET) networks.

Two seventh-generation game consoles, Nintendo's Wii [7]  and Sony's PlayStation 3, use

Bluetooth for their respective wireless controllers.

Dial-up internet access on personal computers or PDAs using a data-capable mobile phone as a

wireless modem like Novatel Mifi.

Short range transmission of health sensor data from medical devices to mobile phone, set-top

box or dedicated telehealthdevices [8] .

[edit]Bluetooth vs. Wi-Fi IEEE 802.11 in networking

Bluetooth and Wi-Fi have many applications in today's offices, homes, and on the move: setting up

networks, printing, or transferring presentations and files from PDAs to computers. Both are versions of

unlicensed wireless technology.

Wi-Fi is intended for resident equipment and its applications. The category of applications is outlined

as WLAN, the wireless local area networks. Wi-Fi is intended as a replacement for cabling for

general local area network access in work areas.

Bluetooth is intended for non resident equipment and its applications. The category of applications is

outlined as the wireless personal area network (WPAN). Bluetooth is a replacement for cabling in a

variety of personally carried applications in any ambience.

[edit]Bluetooth devices

A Bluetooth USB dongle with a 100 m range.

Bluetooth exists in many products, such as telephones, the Wii, PlayStation 3, PSP Go, Lego Mindstorms

NXT and recently in some high definition watches[citation needed], modems and headsets. The technology is

useful when transferring information between two or more devices that are near each other in low-

bandwidth situations. Bluetooth is commonly used to transfer sound data with telephones (i.e., with a

Bluetooth headset) or byte data with hand-held computers (transferring files).

Bluetooth protocols simplify the discovery and setup of services between devices. Bluetooth devices can

advertise all of the services they provide. This makes using services easier because more of the security,

network address and permission configuration can be automated than with many other network types.

[edit]Wi-Fi

Main article: Wi-Fi

Wi-Fi is a traditional Ethernet network, and requires configuration to set up shared resources, transmit

files, and to set up audio links (for example, headsets and hands-free devices). Wi-Fi uses the same radio

frequencies as Bluetooth, but with higher power, resulting in a stronger connection. Wi-Fi is sometimes

called "wireless Ethernet." This description is accurate, as it also provides an indication of its relative

strengths and weaknesses. Wi-Fi requires more setup but is better suited for operating full-scale

networks; it enables a faster connection, better range from the base station, and better security than

Bluetooth.

[edit]Computer requirements

A typical Bluetooth USB dongle.

An internal notebook Bluetooth card (14×36×4 mm).

A personal computer must have a Bluetooth adapter in order to communicate with other Bluetooth

devices (such as mobile phones, mice and keyboards). While some desktop computers and most

recent laptops come with a built-in Bluetooth adapter, others will require an external one in the form of

a dongle.

Unlike its predecessor, IrDA, which requires a separate adapter for each device, Bluetooth allows multiple

devices to communicate with a computer over a single adapter.

Operating system support

For more details on this topic, see Bluetooth stack.

Apple has supported Bluetooth since Mac OS X v10.2 which was released in 2002.[9]

For Microsoft platforms, Windows XP Service Pack 2 and later releases have native support for

Bluetooth. Previous versions required users to install their Bluetooth adapter's own drivers, which were

not directly supported by Microsoft.[10] Microsoft's own Bluetooth dongles (packaged with their Bluetooth

computer devices) have no external drivers and thus require at least Windows XP Service Pack 2.

Linux has two popular Bluetooth stacks, BlueZ and Affix. The BlueZ[11] stack is included with most Linux

kernels and was originally developed by Qualcomm. The Affix stack was developed

by Nokia. FreeBSD features Bluetooth support since its 5.0 release. NetBSD features Bluetooth support

since its 4.0 release. Its Bluetooth stack has been ported to OpenBSD as well.

Mobile phone requirements

A mobile phone that is Bluetooth enabled is able to pair with many devices. To ensure the broadest

support of feature functionality together with legacy device support, the Open Mobile Terminal

Platform (OMTP) forum has recently published a recommendations paper, entitled "Bluetooth Local

Connectivity"; see external links below to download this paper.

Specifications and features

The Bluetooth specification was developed in 1994 by Jaap Haartsen and Sven Mattisson, who were

working for Ericsson Mobile Platforms inLund, Sweden.[12][citation needed] The specification is based

on frequency-hopping spread spectrum technology.

The specifications were formalized by the Bluetooth Special Interest Group (SIG). The SIG was formally

announced on May 20, 1998. Today it has a membership of over 11,000 companies worldwide. It was

established by Ericsson, IBM, Intel, Toshiba, and Nokia, and later joined by many other companies.

Bluetooth 1.0 and 1.0B

Versions 1.0 and 1.0B had many problems, and manufacturers had difficulty making their products

interoperable. Versions 1.0 and 1.0B also included mandatory Bluetooth hardware device address

(BD_ADDR) transmission in the Connecting process (rendering anonymity impossible at the protocol

level), which was a major setback for certain services planned for use in Bluetooth environments.

Bluetooth 1.1

Ratified as IEEE Standard 802.15.1-2002.

Many errors found in the 1.0B specifications were fixed.

Added support for non-encrypted channels.

Received Signal Strength Indicator (RSSI).

Bluetooth 1.2

This version is backward compatible with 1.1 and the major enhancements include the following:

Faster Connection and Discovery

Adaptive frequency-hopping spread spectrum (AFH), which improves resistance to radio

frequency interference by avoiding the use of crowded frequencies in the hopping sequence.

Higher transmission speeds in practice, up to 721 kbit/s, than in 1.1.

Extended Synchronous Connections (eSCO), which improve voice quality of audio links by

allowing retransmissions of corrupted packets, and may optionally increase audio latency to provide

better support for concurrent data transfer.

Host Controller Interface  (HCI) support for three-wire UART.

Ratified as IEEE Standard 802.15.1-2005.

Introduced Flow Control and Retransmission Modes for L2CAP.

Bluetooth 2.0 + EDR

This version of the Bluetooth specification was released on November 10, 2004. It is backward

compatible with the previous version 1.2. The main difference is the introduction of an Enhanced Data

Rate (EDR) for faster data transfer. The nominal rate of EDR is about 3 megabits per second, although

the practical data transfer rate is 2.1 megabits per second.[13] The additional throughput is obtained by

using a different radio technology for transmission of the data. Standard, or Basic Rate, transmission

uses Gaussian Frequency Shift Keying (GFSK) modulation of the radio signal with a gross air data rate of

1 Mbit/s. EDR uses a combination of GFSK and Phase Shift Keying modulation (PSK) with two variants,

π/4-DQPSK and 8DPSK. These have gross air data rates of 2, and 3 Mbit/s respectively. [14]

According to the 2.0 + EDR specification, EDR provides the following benefits:

Three times the transmission speed (2.1 Mbit/s) in some cases.

Reduced complexity of multiple simultaneous connections due to additional bandwidth.

Lower power consumption through a reduced duty cycle.

The Bluetooth Special Interest Group (SIG) published the specification as "Bluetooth 2.0 + EDR" which

implies that EDR is an optional feature. Aside from EDR, there are other minor improvements to the 2.0

specification, and products may claim compliance to "Bluetooth 2.0" without supporting the higher data

rate. At least one commercial device, the HTC TyTN Pocket PC phone, states "Bluetooth 2.0 without

EDR" on its data sheet.[15]

Bluetooth 2.1 + EDR

Bluetooth Core Specification Version 2.1 + EDR is fully backward compatible with 1.2, and was adopted

by the Bluetooth SIG on July 26, 2007.[14] It supports theoretical data transfer speeds of up to 3 Mb/s. This

specification includes the following features:

Extended inquiry response (EIR)

Provides more information during the inquiry procedure to allow better filtering of devices before

connection. This information may include the name of the device, a list of services the device

supports, the transmission power level used for inquiry responses, and manufacturer defined

data.

Sniff subrating

Reduces the power consumption when devices are in the sniff low-power mode, especially on

links with asymmetric data flows. Human interface devices (HID) are expected to benefit the

most, with mouse and keyboard devices increasing their battery life by a factor of 3 to 10. [citation

needed] It lets devices decide how long they will wait before sending keepalive messages to one

another. Previous Bluetooth implementations featured keep alive message frequencies of up to

several times per second. In contrast, the 2.1 + EDR specification allows pairs of devices to

negotiate this value between them to as infrequently as once every 10 seconds.

Encryption pause/resume (EPR)

Enables an encryption key to be changed with less management required by the Bluetooth host.

Changing an encryption key must be done for a role switch of an encrypted an ACL link, or every

23.3 hours (one Bluetooth day) encryption is enabled on an ACL link. Before this feature was

introduced, when an encryption key is refreshed the Bluetooth host would be notified of a brief

gap in encryption while the new key was generated; so the Bluetooth host was required to handle

pausing data transfer (however data requiring encryption may already have been sent before the

notification that encryption is disabled has been received). With EPR, the Bluetooth host is not

notified of the gap, and the Bluetooth controller ensures that no unencrypted data is transferred

while they key is refreshed.

Secure simple pairing (SSP)

Radically improves the pairing experience for Bluetooth devices, while increasing the use and

strength of security. See the section onPairing below for more details. It is expected that this

feature will significantly increase the use of Bluetooth.[16]

Near field communication (NFC) cooperation

Automatic creation of secure Bluetooth connections when NFC radio interface is also available.

This functionality is part of SSP where NFC is one way of exchanging pairing information. For

example, a headset should be paired with a Bluetooth 2.1 + EDR phone including NFC just by

bringing the two devices close to each other (a few centimeters). Another example is automatic

uploading of photos from a mobile phone or camera to a digital picture frame just by bringing the

phone or camera close to the frame.[17][18]

Non-Automatically-Flushable Packet Boundary Flag (PBF)

Using this feature L2CAP may support both isochronous (A2DP media Streaming) and

asynchronous data flows (AVRCP Commands) over the same logical link by marking packets as

automatically-flushable or non-automatically-flushable by setting the appropriate value for the

Packet_Boundary_Flag in the HCI ACL Data Packet

Bluetooth 3.0 + HS

The 3.0 + HS specification[14] was adopted by the Bluetooth SIG on April 21, 2009. It

supports theoretical data transfer speeds of up to 24 Mb/s. Its main new feature is

AMP (Alternate MAC/PHY), the addition of 802.11 as a high speed transport. Two

technologies had been anticipated for AMP: 802.11 and UWB, but UWB is missing

from the specification.[19]

Alternate MAC/PHY

Enables the use of alternative MAC and PHYs for transporting Bluetooth profile

data. The Bluetooth Radio is still used for device discovery, initial connection and

profile configuration, however when lots of data needs to be sent, the high speed

alternate MAC PHY (802.11, typically associated with Wi-Fi) will be used to

transport the data. This means that the proven low power connection models of

Bluetooth are used when the system is idle, and the low power per bit radios are

used when lots of data needs to be sent.

Unicast connectionless data

Permits service data to be sent without establishing an explicit L2CAP channel. It is

intended for use by applications that require low latency between user action and

reconnection/transmission of data. This is only appropriate for small amounts of

data.

Read encryption key size

Introduces a standard HCI command for a Bluetooth host to query the encryption

key size on an encrypted ACL link. The encryption key size used on a link is

required for the SIM Access Profile, so generally Bluetooth controllers provided this

feature in a proprietary manner. Now the information is available over the standard

HCI interface.

Enhanced Power Control

Updates the power control feature to remove the open loop power control, and also

to clarify ambiguities in power control introduced by the new modulation schemes

added for EDR. Enhanced power control removes the ambiguities by specifying the

behaviour that is expected. The feature also adds closed loop power control,

meaning RSSI filtering can start as the response is received. Additionally, a "go

straight to maximum power" request has been introduced, this is expected to deal

with the headset link loss issue typically observed when a user puts their phone into

a pocket on the opposite side to the headset.

Bluetooth low energy

Main article: Bluetooth low energy

On April 20, 2009, Bluetooth SIG presented the new Bluetooth low energy as an

entirely additional protocol stack, compatible with other existing Bluetooth protocol

stacks. The preceding naming as Wibree and Bluetooth ULP (Ultra Low Power) has

not been adopted as the final naming. The soon to be launched version of the

Bluetooth core specification is being referred to as Bluetooth low energy.

On June 12, 2007, Nokia and Bluetooth SIG had announced that Wibree will be a

part of the Bluetooth specification, as an ultra-low power Bluetooth technology.

[20] Expected use cases include watches displaying Caller ID information, sports

sensors monitoring the wearer's heart rate during exercise, and medical devices.

The Medical Devices Working Group is also creating a medical devices profile and

associated protocols to enable this market. Bluetooth low energy technology is

designed for devices to have a battery life of up to one year.

Future

Broadcast channel

Enables Bluetooth information points. This will drive the adoption of Bluetooth into

mobile phones, and enable advertising models based around users pulling

information from the information points, and not based around the object push

model that is used in a limited way today.

Topology management

Enables the automatic configuration of the piconet topologies especially

in scatternet situations that are becoming more common today. This should all be

invisible to users of the technology, while also making the technology "just work."

 improvements

Enable audio and video data to be transmitted at a higher quality, especially when

best effort traffic is being transmitted in the samepiconet.

UWB for AMP

Main article: ultra-wideband

The high speed (AMP) feature of Bluetooth 3.0 is based on 802.11, but the AMP

mechanism was designed to be usable with other radios as well. It was originally

intended for UWB, but the WiMedia Alliance, the body responsible for the flavor of

UWB intended for Bluetooth, announced in March 2009 that it was disbanding.

On March 16, 2009, the WiMedia Alliance announced it was entering into

technology transfer agreements for the WiMedia Ultra-wideband(UWB)

specifications. WiMedia will transfer all current and future specifications, including

work on future high speed and power optimized implementations, to the Bluetooth

Special Interest Group (SIG), Wireless USB Promoter Group and the USB

Implementers Forum. After the successful completion of the technology transfer,

marketing and related administrative items, the WiMedia Alliance will cease

operations.[21]

In October 2009 the Bluetooth Special Interest Group has dropped development of

UWB as part of the alternative MAC/PHY, Bluetooth 3.0/High Speed solution. A

small, but significant, number of former WiMedia members had not and would not

sign up to the necessary agreements for the IP transfer. The Bluetooth group is now

in the process of evaluating other options for its longer term roadmap.[22]

Technical information

Bluetooth protocol stack

Main articles: Bluetooth stack and Bluetooth protocols

"Bluetooth is defined as a layer protocol architecture consisting of core protocols,

cable replacement protocols, telephony control protocols, and adopted

protocols."[23] Mandatory protocols for all Bluetooth stacks are: LMP, L2CAP and

SDP. Additionally, these protocols are almost universally supported: HCI and

RFCOMM.

LMP (Link Management Protocol)

Used for control of the radio link between two devices. Implemented on the

controller.

L2CAP (Logical Link Control & Adaptation Protocol)

Used to multiplex multiple logical connections between two devices using different

higher level protocols. Provides segmentation and reassembly of on-air packets.

In Basic mode, L2CAP provides packets with a payload configurable up to 64kB,

with 672 bytes as the default MTU, and 48 bytes as the minimum mandatory

supported MTU.

In Retransmission & Flow Control modes, L2CAP can be configured for reliable or

isochronous data per channel by performing retransmissions and CRC checks.

Bluetooth Core Specification Addendum 1 adds two additional L2CAP modes to the

core specification. These modes effectively deprecate original Retransmission and

Flow Control modes:

Enhanced Retransmission Mode (ERTM): This mode is an improved version

of the original retransmission mode. This mode provides a reliable L2CAP

channel.

Streaming Mode (SM): This is a very simple mode, with no retransmission or

flow control. This mode provides an unreliable L2CAP channel.

Reliability in any of these modes is optionally and/or additionally guaranteed by the

lower layer Bluetooth BDR/EDR air interface by configuring the number of

retransmissions and flush timeout (time after which the radio will flush packets). In-

order sequencing is guaranteed by the lower layer.

Only L2CAP channels configured in ERTM or SM may be operated over AMP

logical links.

ISDP (Service Discovery Protocol)

Used to allow devices to discover what services each other support, and what

parameters to use to connect to them. For example, when connecting a mobile

phone to a Bluetooth headset, SDP will be used to determine which Bluetooth

profiles are supported by the headset (Headset Profile, Hands Free

Profile, Advanced Audio Distribution Profile etc) and the protocol multiplexer

settings needed to connect to each of them. Each service is identified by

a Universally Unique Identifier (UUID), with official services (Bluetooth profiles)

assigned a short form UUID (16 bits rather than the full 128)

HCI (Host/Controller Interface)

Standardised communication between the host stack (e.g., a PC or mobile phone

OS) and the controller (the Bluetooth IC). This standard allows the host stack or

controller IC to be swapped with minimal adaptation.

There are several HCI transport layer standards, each using a different hardware

interface to transfer the same command, event and data packets. The most

commonly used are USB (in PCs) and UART (in mobile phones and PDAs).

In Bluetooth devices with simple functionality (e.g., headsets) the host stack and

controller can be implemented on the same microprocessor. In this case the HCI is

optional, although often implemented as an internal software interface.

RFCOMM (Cable replacement protocol)

Radio frequency communications (RFCOMM) is the cable replacement protocol

used to create a virtual serial data stream. RFCOMM provides for binary data

transport and emulates EIA-232 (formerly RS-232) control signals over the

Bluetooth baseband layer.

RFCOMM provides a simple reliable data stream to the user, similar to TCP. It is

used directly by many telephony related profiles as a carrier for AT commands, as

well as being a transport layer for OBEX over Bluetooth.

Many Bluetooth applications use RFCOMM because of its widespread support and

publicly available API on most operating systems. Additionally, applications that

used a serial port to communicate can be quickly ported to use RFCOMM.

BNEP (Bluetooth Network Encapsulation Protocol)

BNEP is used to transfer another protocol stack's data via an L2CAP channel. Its

main purpose is the transmission of IP packets in the Personal Area Networking

Profile. BNEP performs a similar function to SNAP in Wireless LAN.

AVCTP (Audio/Visual Control Transport Protocol)

Used by the remote control profile to transfer AV/C commands over an L2CAP

channel. The music control buttons on a stereo headset use this protocol to control

the music player

AVDTP (Audio/Visual Data Transport Protocol)

Used by the advanced audio distribution profile to stream music to stereo headsets

over an L2CAP channel. Intended to be used by video distribution profile.

Telephone control protocol

Telephony control protocol-binary (TCS BIN) is the bit-oriented protocol that defines

the call control signaling for the establishment of voice and data calls between

Bluetooth devices. Additionally, "TCS BIN defines mobility management procedures

for handling groups of Bluetooth TCS devices."

TCS-BIN is only used by the cordless telephony profile, which failed to attract

implementers. As such it is only of historical interest.

Adopted protocols

Adopted protocols are defined by other standards-making organizations and

incorporated into Bluetooth’s protocol stack, allowing Bluetooth to create protocols

only when necessary. The adopted protocols include:

Point-to-Point Protocol (PPP)

Internet standard protocol for transporting IP datagrams over a point-to-point link

TCP/IP/UDP

Foundation Protocols for TCP/IP protocol suite

Object Exchange Protocol (OBEX)

Session-layer protocol for the exchange of objects, providing a model for object and

operation representation

Wireless Application Environment/Wireless Application Protocol (WAE/WAP)

WAE specifies an application framework for wireless devices and WAP is an open

standard to provide mobile users access to telephony and information services.[23]

Communication and connection

A master Bluetooth device can communicate with up to seven devices in a Wireless

User Group. This network group of up to eight devices is called a piconet.

A piconet is an ad-hoc computer network, using Bluetooth technology protocols to

allow one master device to interconnect with up to seven active devices. Up to 255

further devices can be inactive, or parked, which the master device can bring into

active status at any time.

At any given time, data can be transferred between the master and one other

device, however, the devices can switch roles and the slave can become the master

at any time. The master switches rapidly from one device to another in a round-

robin fashion. (Simultaneous transmission from the master to multiple other devices

is possible, but not used much.)

The Bluetooth specification allows connecting two or more piconets together to form

a scatternet, with some devices acting as a bridge by simultaneously playing the

master role in one piconet and the slave role in another.

Many USB Bluetooth adapters are available, some of which also include

an IrDA adapter. Older (pre-2003) Bluetooth adapters, however, have limited

services, offering only the Bluetooth Enumerator and a less-powerful Bluetooth

Radio incarnation. Such devices can link computers with Bluetooth, but they do not

offer much in the way of services that modern adapters do.

Baseband Error Correction

Three types of error correction are implemented in Bluetooth systems,

1/3 rate forward error correction (FEC)

2/3 rate FEC

Automatic repeat-request (ARQ)

Computer networking

Network cards such as this one can transmit and receive data at high rates over various types of

network cables. This card is a 'Combo' card which supports three cabling standards.

This article is about computer networking, the discipline of engineering computer

networks. For the article on computer networks, see Computer network.

"Datacom" redirects here. For other uses, see Datacom (disambiguation).

Computer networking is the engineering discipline concerned with communication

betweencomputer systems or devices. Networking, routers, routing protocols, and

networking over the public Internet have their specifications defined in documents

called RFCs.[1] Computer networking is sometimes considered a sub-discipline

of telecommunications, computer science, information technology and/or computer

engineering. Computer networks rely heavily upon the theoretical and practical

application of these scientific and engineering disciplines. There are three types of

networks: 1.Internet. 2.Intranet. 3.Extranet. A computer network is any set of

computers or devices connected to each other with the ability to exchange data.

[2]Examples of different networks are:

Local area network  (LAN), which is usually a small network constrained to a

small geographic area. An example of a LAN would be a computer network

within a building.

Metropolitan area network  (MAN), which is used for medium size area.

examples for a city or a state.

Wide area network  (WAN) that is usually a larger network that covers a

large geographic area.

Wireless LANs and WANs  (WLAN & WWAN) are the wireless equivalent of

the LAN and WAN.

All networks are interconnected to allow communication with a variety of different

kinds of media, including twisted-pair copper wire cable,coaxial cable, optical

fiber, power lines and various wireless technologies.[3] The devices can be

separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g.

via the interconnections of the Internet [4] ).

Views of networks

Users and network administrators often have different views of their networks.

Often, users who share printers and some servers form a workgroup, which usually

means they are in the same geographic location and are on the same LAN.

A community of interest has less of a connection of being in a local area, and

should be thought of as a set of arbitrarily located users who share a set of servers,

and possibly also communicate via peer-to-peer technologies.

Network administrators see networks from both physical and logical perspectives.

The physical perspective involves geographic locations, physical cabling, and the

network elements (e.g., routers, bridges and application layer gateways that

interconnect the physical media. Logical networks, called, in the TCP/IP

architecture, subnets, map onto one or more physical media. For example, a

common practice in a campus of buildings is to make a set of LAN cables in each

building appear to be a common subnet, using virtual LAN (VLAN) technology.

Both users and administrators will be aware, to varying extents, of the trust and

scope characteristics of a network. Again using TCP/IP architectural terminology,

an intranet is a community of interest under private administration usually by an

enterprise, and is only accessible by authorized users (e.g. employees).[5] Intranets

do not have to be connected to the Internet, but generally have a limited connection.

An extranetis an extension of an intranet that allows secure communications to

users outside of the intranet (e.g. business partners, customers).[5]

Informally, the Internet is the set of users, enterprises,and content providers that are

interconnected by Internet Service Providers (ISP). From an engineering standpoint,

the Internet is the set of subnets, and aggregates of subnets, which share the

registered IP address space and exchange information about the reachability of

those IP addresses using the Border Gateway Protocol. Typically, the human-

readable names of servers are translated to IP addresses, transparently to users,

via the directory function of the Domain Name System (DNS).

Over the Internet, there can be business-to-business (B2B), business-to-consumer

(B2C) and consumer-to-consumer (C2C) communications. Especially when money

or sensitive information is exchanged, the communications are apt to

be secured by some form of communications security mechanism. Intranets and

extranets can be securely superimposed onto the Internet, without any access by

general Internet users, using secure Virtual Private Network (VPN) technology.

When used for gaming one computer will have to be the server while the others play

through it.

[edit]History of Computer Networks

Before the advent of computer networks that were based upon some type

of telecommunications system, communication between calculation machines and

history of computer hardware early computers was performed by human users by

carrying instructions between them. Many of the social behavior seen in today's

Internet was demonstrably present in nineteenth-century and arguably in even

earlier networks using visual signals.The Victorian Internet

In September 1940 George Stibitz used a teletype machine to send instructions for

a problem set from his Model at Dartmouth College in New Hampshire to his

Complex Number Calculator in New York and received results back by the same

means. Linking output systems like teletypes to computers was an interest at

the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider

was hired and developed a working group he called the "Intergalactic Network", a

precursor to the ARPANet.

In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing

System for distributed users of large computer systems. The same year, at MIT, a

research group supported by General Electric and Bell Labs used a computer

DEC's to route and manage telephone connections.

Throughout the 1960s Leonard Kleinrock,Paul Baran and Donald Davies

independently conceptualized and developed network systems which used

datagrams or Packet information technology that could be used in a network

between computer systems.

1965 Thomas Merrill and Lawrence G. Roberts created the first wide area network

(WAN).

The first widely used PSTN switch that used true computer control was the Western

Electric introduced in 1965.

In 1969 the University of California at Los Angeles, SRI (in Stanford), University of

California at Santa Barbara, and the University of Utah were connected as the

beginning of the ARPANet network using 50 kbit/s circuits. Commercial services

using X.25 were deployed in 1972, and later used as an underlying infrastructure for

expanding TCP/IP networks.

Computer networks, and the technologies needed to connect and communicate

through and between them, continue to drive computer hardware, software, and

peripherals industries. This expansion is mirrored by growth in the numbers and

types of users of networks from the researcher to the home user.

Today, computer networks are the core of modern communication. All modern

aspects of the Public Switched Telephone Network (PSTN) are computer-

controlled, and telephony increasingly runs over the Internet Protocol, although not

necessarily the public Internet. The scope of communication has increased

significantly in the past decade and this boom in communications would not have

been possible without the progressively advancing computer network.

Networking methods

One way to categorize computer networks is by their geographic scope, although

many real-world networks interconnect Local Area Networks(LAN) via Wide Area

Networks (WAN) and wireless networks (WWAN). These three (broad) types are:

Local area network (LAN)

A local area network is a network that spans a relatively small space and provides

services to a small number of people.

A peer-to-peer or client-server method of networking may be used. A peer-to-peer

network is where each client shares their resources with other workstations in the

network. Examples of peer-to-peer networks are: Small office networks where

resource use is minimal and a home network. A client-server network is where

every client is connected to the server and each other. Client-server networks use

servers in different capacities. These can be classified into two types:

1. Single-service servers

2. Print server

The server performs one task such as file server, while other servers can not only

perform in the capacity of file servers and print servers, but also can conduct

calculations and use them to provide information to clients (Web/Intranet Server).

Computers may be connected in many different ways, including Ethernet cables,

Wireless networks, or other types of wires such as power lines or phone lines.

The ITU-T G.hn standard is an example of a technology that provides high-speed

(up to 1 Gbit/s) local area networking over existing home wiring (power lines, phone

lines and coaxial cables).

Wide area network (WAN)

A wide area network is a network where a wide variety of resources are deployed

across a large domestic area or internationally. An example of this is a multinational

business that uses a WAN to interconnect their offices in different countries. The

largest and best example of a WAN is the Internet, which is a network composed of

many smaller networks. The Internet is considered the largest network in the world.

[6]. The PSTN(Public Switched Telephone Network) also is an extremely large

network that is converging to use Internet technologies, although not necessarily

through the public Internet.

A Wide Area Network involves communication through the use of a wide range of

different technologies. These technologies include Point-to-Point WANs such as

Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC), Frame

Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical

Network). The difference between the WAN technologies is based on the switching

capabilities they perform and the speed at which sending and receiving bits of

information (data) occur.

Metropolitan area network (MAN)

A metropolitan network is a network that is too large for even the largest of LAN's

but is not on the scale of a WAN. It also integrates two or more LAN networks over

a specific geographical area ( usually a city ) so as to increase the network and the

flow of communications. The LAN's in question would usually be connected via "

backbone " lines.

For more information on WANs, see Frame Relay, ATM and Sonet.

Wireless networks (WLAN, WWAN)

A wireless network is basically the same as a LAN or a WAN but there are no wires

between hosts and servers. The data is transferred over sets of radio transceivers.

These types of networks are beneficial when it is too costly or inconvenient to run

the necessary cables. For more information, see Wireless LAN and Wireless wide

area network. The media access protocols for LANs come from the IEEE.

The most common IEEE 802.11 WLANs cover, depending on antennas, ranges

from hundreds of meters to a few kilometers. For larger areas,

either communications satellites of various types, cellular radio, or wireless local

loop (IEEE 802.16) all have advantages and disadvantages. Depending on the type

of mobility needed, the relevant standards may come from the IETF or the ITU.

Network topology

The network topology defines the way in which computers, printers, and other

devices are connected, physically and logically. A network topology describes the

layout of the wire and devices as well as the paths used by data transmissions.

Network topology has two types:

Physical

logical

Commonly used topologies include:

Bus

Star

Tree (hierarchical)

Linear

Ring

Mesh

partially connected

fully connected (sometimes known as fully redundant)

The network topologies mentioned above are only a general representation of the

kinds of topologies used in computer network and are considered basic topologies.

As a matter of fact networking is defined by the standard of OSI (Open Systems

Interconnection) reference for communications. The OSI model consists of seven

layers. Each layer has its own function. The OSI model layers are Application,

Presentation, Session, Transport, Network, Data Link, and Physical. The upper

layers (Application, Presentation, Session) of the OSI model concentrate on the

application while the lower layers (transport, network, data link, and physical) focus

on signal flow of data from origin to destination. The Application layer defines the

medium that communications software and any applications need to communicate

to other computers. Layer 6 which is the presentation layer focuses on defining data

formats such as text, jpeg, gif, and binary. An example of this layer would be

displaying a picture that was received in an e-mail. The 5th Layer is the session

layer which establishes how to start, control, and end links or conversations. The

transport layer includes protocols that allow it to provide functions in many different

areas such as: error recovery, segmentation, and reassembly. The network layers

primary job is the end to end delivery of data packets. To do this, the network layer

relies on logical addressing so that the origin and destination point can both be

recognized. An example of this would be, ip running in a router’s job is to examine

the destination address, compare the address to the ip routing table, separate the

packet into smaller chunks for transporting purposes, and then deliver the packet to

the correct receiver. Layer 2 is the data link layer, which sets the standards for data

being delivered across a link or medium. The 1st layer is the physical layer which

deals with the physical characteristics of the transmission of data such as the

network card and network cable type. An easy way to remember the layers of OSI is

to remember All People Seem To Need Data Processing (Layers 7 to 1).

Computer networking device

A full list of Computer networking devices are units that mediate data in

a computer network. Computer networking devices are also called network

equipment, Intermediate Systems (IS) or InterWorking Unit (IWU). Units which are

the last receiver or generate data are called hosts ordata terminal equipment.

[edit]List of computer networking devices

Common basic networking devices:

Gateway : device sitting at a network node for interfacing with another

network that uses different protocols. Works on OSI layers 4 to 7.

Router : a specialized network device that determines the next network point

to which to forward a data packet toward its destination. Unlike a gateway, it

cannot interface different protocols. Works on OSI layer 3.

Bridge : a device that connects multiple network segments along the data

link layer. Works on OSI layer 2.

Switch : a device that allocates traffic from one network segment to certain

lines (intended destination(s)) which connect the segment to another network

segment. So unlike a hub a switch splits the network traffic and sends it to

different destinations rather than to all systems on the network. Works on OSI

layer 2.

Hub : connects multiple Ethernet segments together making them act as a

single segment. When using a hub, every attached device shares the

same broadcast domain and the same collision domain. Therefore, only

one computer connected to the hub is able to transmit at a time. Depending on

the network topology, the hub provides a basic level 1 OSI model connection

among the network objects (workstations, servers, etc). It provides bandwidth

which is shared among all the objects, compared to switches, which provide a

dedicated connection between individual nodes. Works on OSI layer 1.

Repeater : device to amplify or regenerate digital signals received while

setting them from one part of a network into another. Works on OSI layer 1.

Some hybrid network devices:

Multilayer Switch : a switch which, in addition to switching on OSI layer 2,

provides functionality at higher protocol layers.

Protocol Converter : a hardware device that converts between two different

types of transmissions, such as asynchronous and synchronous transmissions.

Bridge Router (Brouter): Combine router and bridge functionality and are

therefore working on OSI layers 2 and 3.

Digital media receiver : Connects a computer network to a home theatre

Hardware or software components that typically sit on the connection point of

different networks, e.g. between an internal network and an external network:

Proxy : computer network service which allows clients to make indirect

network connections to other network services

Firewall : a piece of hardware or software put on the network to prevent

some communications forbidden by the network policy

Network Address Translator : network service provide as hardware or

software that converts internal to external network addresses and vice versa

Other hardware for establishing networks or dial-up connections:

Multiplexer : device that combines several electrical signals into a single

signal

Network Card : a piece of computer hardware to allow the attached

computer to communicate by network

Modem : device that modulates an analog "carrier" signal (such as sound),

to encode digital information, and that also demodulates such a carrier signal to

decode the transmitted information, as a computer communicating with another

computer over the telephone network

ISDN terminal adapter  (TA): a specialized gateway for ISDN

Line Driver : a device to increase transmission distance by amplifying the

signal. Base-band networks only.mohit

Network Device Connectivity

Home network

A home network or home area network (HAN) is a residential local area network.

It is used for communication between digital devices typically deployed in the home,

usually a small number of personal computers and accessories, such as printers

and mobile computing devices. An important function is the sharing of Internet

access, often a broadband service through a cable tv or Digital Subscriber

Line (DSL) provider.

More recently telephone companies such as AT&T and British Telecom have been

using home networking to provide triple play services (voice, video and data) to

customers. These use IPTVto provide the video service. The home network usually

operates over the existing home wiring (coax in North America, phone wires in multi

dwelling units (MDU) and powerline in Europe). These home networks are often

professionally installed and managed by the telco. The ITU-T G.hn  standard, which

provides high-speed (up to 1 Gbit/s) local area networking over existing home wiring

(power lines, phone lines and coaxial cables), is an example of a home networking

technology designed specifically for IPTV delivery.

Network devices

 home network may consist of the following components:

A broadband modem for connection to the internet (either a DSL

modem using the phone line, or cable modem using the cable

internetconnection).

A residential gateway (sometimes called a router) connected between the

broadband modem and the rest of the network. This enables multiple devices to

connect to the internet simultaneously. Residential gateways, hubs/switches,

DSL modems, and wireless access points are often combined.

A PC, or multiple PCs including laptops

A wireless access point, usually implemented as a feature rather than a

separate box, for connecting wireless devices

Entertainment peripherals - an increasing number of devices can be

connected to the home network, including DVRs like TiVo, digital audio

players, games machines, stereo system, and IP set-top box.

Internet Phones (VoIP)

A network bridge connects two networks together, often giving a wired

device, e.g. Xbox, access to a wireless network.

A network hub/switch - a central networking hub containing a number

of Ethernet ports for connecting multiple networked devices

A network attached storage (NAS) device can be used for storage on the

network.

A print server can be used to share printers among computers on the

network.

Older devices may not have the appropriate connector to the network. USB and PCI

network controllers can be installed in some devices to allow them to connect to

networks.

Network devices may also be configured from a computer. For example, broadband

modems are often configured through a web client on a networked PC. As

networking technology evolves, more electronic devices and home appliances are

becoming Internet ready and accessible through the home network. Set-top

boxes from cable TV providers already have USB and Ethernet ports "for future

use".

Network media

Ethernet cables are the standard medium for networks. However, homes are often

more difficult to wire than office environments, and other technologies are being

developed which don't require new wires.

Home networking may use

Ethernet Category 5 cable, Category 6 cable - for speeds of 10 Mbit/s, 100

Mbit/s, or 1 Gbit/s.

Wi-Fi  Wireless LAN connections - for speeds up to 248 Mbit/s, dependent

on signal strength and wireless standard.

Coaxial cables (TV antennas) - for speeds of 270 Mbit/s (see Multimedia

over Coax Alliance or 320 Mbit/s see HomePNA)

Electrical wiring - for speeds of 14 Mbit/s to 200 Mbit/s (see Power line

communication)

Phone wiring - for speeds of 160 Mbit/s (see HomePNA)

Fiber optics - although rare, new homes are beginning to include fiber

optics for future use. Optical networks generally use Ethernet.

All home wiring (coax, powerline and phone wires) - future standard for

speeds up to 1 Gbit/s being developed by the ITU-T (see G.hn)

Ethernet and Wireless are the most common standards. As the demand for home

networks has increased, the other alliances have formed to produce standards for

networking alternatives.

IP address

An Internet Protocol (IP) address is a numerical label that is assigned to devices

participating in a computer network utilizing the Internet Protocol for communication

between its nodes.[1] An IP address serves two principal functions in networking:

host or network interfaceidentification and location addressing. The role of the IP

address has also been characterized as follows: "A name indicates what we seek.

An address indicates where it is. A route indicates how to get there."[2]

The original designers of TCP/IP defined an IP address as a 32-bit number[1] and

this system, known as Internet Protocol Version 4 or IPv4, is still in use today.

However, due to the enormous growth of the Internet and the resulting depletion of

available addresses, a new addressing system (IPv6), using 128 bits for the

address, was developed in 1995[3] and last standardized by RFC 2460 in 1998.

[4] Although IP addresses are stored as binary numbers, they are usually displayed

in human-readable notations, such as 208.77.188.166 (for IPv4), and

2001:db8:0:1234:0:567:1:1 (for IPv6).

The Internet Protocol also has the task of routing data packets between networks,

and IP addresses specify the locations of the source and destination nodes in

the topology of the routing system. For this purpose, some of the bits in an IP

address are used to designate asubnetwork. The number of these bits is indicated

in CIDR notation, appended to the IP address, e.g., 208.77.188.166/24.

With the development of private networks and the threat of IPv4 address

exhaustion, a group of private address spaces was set aside by RFC 1918.

These private addresses may be used by anyone on private networks. They are

often used with network address translators to connect to the global public Internet.

The Internet Assigned Numbers Authority (IANA) manages the IP address space

allocations globally. IANA works in cooperation with fiveRegional Internet

Registries (RIRs) to allocate IP address blocks to Local Internet Registries (Internet

service providers) and other entities.

IP versions

Two versions of the Internet Protocol (IP) are currently in use (see IP version

history for details), IP Version 4 and IP Version 6. Each version defines an IP

address differently. Because of its prevalence, the generic term IP address typically

still refers to the addresses defined by IPv4.

An illustration of an IP address (version 4), in both dot-decimal notation and binary.

IP version 4 addresses

Main article: IPv4#Addressing

IPv4 uses 32-bit (4-byte) addresses, which limits the address space to

4,294,967,296 (232) possible unique addresses. IPv4 reserves some addresses for

special purposes such as private networks (~18 million addresses) or multicast

addresses (~270 million addresses). This reduces the number of addresses that

can be allocated to end users and, as the number of addresses available is

consumed, IPv4 address exhaustion is inevitable. This foreseeable shortage was

the primary motivation for developing IPv6, which is in various deployment stages

around the world and is the only strategy for IPv4 replacement and continued

Internet expansion.

IPv4 addresses are usually represented in dot-decimal notation (four numbers, each

ranging from 0 to 255, separated by dots, e.g. 208.77.188.166). Each part

represents 8 bits of the address, and is therefore called an octet. In less common

cases of technical writing, IPv4 addresses may be presented inhexadecimal, octal,

or binary representations. In most representations each octet is converted

individually.

IPv4 subnetting

In the early stages of development of the Internet Protocol,[1] network administrators

interpreted an IP address in two parts, network number portion and host number

portion. The highest order octet (most significant eight bits) in an address was

designated the network number and the rest of the bits were called the rest

field or host identifier and were used for host numbering within a network. This

method soon proved inadequate as additional networks developed that were

independent from the existing networks already designated by a network number. In

1981, the Internet addressing specification was revised with the introduction

of classful network architecture.[2]

Classful network design allowed for a larger number of individual network

assignments. The first three bits of the most significant octet of an IP address was

defined as the class of the address. Three classes (A, B, and C) were defined for

universal unicast addressing. Depending on the class derived, the network

identification was based on octet boundary segments of the entire address. Each

class used successively additional octets in the network identifier, thus reducing the

possible number of hosts in the higher order classes (B and C). The following table

gives an overview of this now obsolete system.

Historical classful network architecture

ClassFirst octet in

binaryRange of first

octetNetwork

IDHost ID

Number of networks

Number of addresses

A 0XXXXXXX 0 - 127 a b.c.d 27 = 128 224 = 16,777,216

B 10XXXXXX 128 - 191 a.b c.d 214 = 16,384 216 = 65,536

C 110XXXXX 192 - 223 a.b.c d 221 = 2,097,152 28 = 256

The articles 'subnetwork' and 'classful network' explain the details of this design.

Although classful network design was a successful developmental stage, it

proved unscalable in the rapid expansion of the Internet and was abandoned

when Classless Inter-Domain Routing (CIDR) was created for the allocation of IP

address blocks and new rules of routing protocol packets using IPv4 addresses.

CIDR is based on variable-length subnet masking (VLSM) to allow allocation and

routing on arbitrary-length prefixes.

Today, remnants of classful network concepts function only in a limited scope as the

default configuration parameters of some network software and hardware

components (e.g. netmask), and in the technical jargon used in network

administrators' discussions.

IPv4 private addresses

Main article: Private network

Early network design, when global end-to-end connectivity was envisioned for

communications with all Internet hosts, intended that IP addresses be uniquely

assigned to a particular computer or device. However, it was found that this was not

always necessary as private networks developed and public address space needed

to be conserved (IPv4 address exhaustion).

Computers not connected to the Internet, such as factory machines that

communicate only with each other via TCP/IP, need not have globally-unique IP

addresses. Three ranges of IPv4 addresses for private networks, one range for

each class (A, B, C), were reserved in RFC 1918. These addresses are not routed

on the Internet and thus their use need not be coordinated with an IP address

registry.

Today, when needed, such private networks typically connect to the Internet

through network address translation (NAT).

IANA-reserved private IPv4 network ranges

Start End No. of addresses

24-bit Block (/8 prefix, 1 x A) 10.0.0.0 10.255.255.255 16,777,216

20-bit Block (/12 prefix, 16 x B) 172.16.0.0 172.31.255.255 1,048,576

16-bit Block (/16 prefix, 256 x C) 192.168.0.0 192.168.255.255 65,536

Any user may use any of the reserved blocks. Typically, a network administrator will

divide a block into subnets; for example, many home routers automatically use a

default address range of 192.168.0.0 - 192.168.0.255 (192.168.0.0/24).

IPv4 address depletion

Main article: IPv4 address exhaustion

The IP version 4 address space is rapidly nearing exhaustion of available, officially

assignable address blocks.

IP version 6 addresses

Main article: IPv6 Addresses

An illustration of an IP address (version 6), in hexadecimaland binary.

The rapid exhaustion of IPv4 address space, despite conservation techniques,

prompted the Internet Engineering Task Force (IETF) to explore new technologies

to expand the Internet's addressing capability. The permanent solution was deemed

to be a redesign of the Internet Protocol itself. This next generation of the Internet

Protocol, aimed to replace IPv4 on the Internet, was eventually named Internet

Protocol Version 6 (IPv6) in 1995[3][4] The address size was increased from 32 to

128 bits or 16 octets, which, even with a generous assignment of network blocks, is

deemed sufficient for the foreseeable future. Mathematically, the new address

space provides the potential for a maximum of 2128, or about 3.403 × 1038 unique

addresses.

The new design is not based on the goal to provide a sufficient quantity of

addresses alone, but rather to allow efficient aggregation of subnet routing prefixes

to occur at routing nodes. As a result, routing table sizes are smaller, and the

smallest possible individual allocation is a subnet for 264 hosts, which is the size of

the square of the size of the entire IPv4 Internet. At these levels, actual address

utilization rates will be small on any IPv6 network segment. The new design also

provides the opportunity to separate the addressing infrastructure of a network

segment—that is the local administration of the segment's available space—from

the addressing prefix used to route external traffic for a network. IPv6 has facilities

that automatically change the routing prefix of entire networks should the global

connectivity or the routing policy change without requiring internal redesign or

renumbering.

The large number of IPv6 addresses allows large blocks to be assigned for specific

purposes and, where appropriate, to be aggregated for efficient routing. With a large

address space, there is not the need to have complex address conservation

methods as used in classless inter-domain routing (CIDR).

All modern desktop and enterprise server operating systems include native support

for the IPv6 protocol, but it is not yet widely deployed in other devices, such as

home networking routers, voice over Internet Protocol (VoIP) and multimedia

equipment, and network peripherals.

Example of an IPv6 address:

2001:0db8:85a3:08d3:1319:8a2e:0370:7334

IPv6 private addresses

Just as IPv4 reserves addresses for private or internal networks, there are blocks of

addresses set aside in IPv6 for private addresses. In IPv6, these are referred to

as unique local addresses (ULA). RFC 4193 sets aside the routing prefix fc00::/7 for

this block which is divided into two /8 blocks with different implied policies (cf. IPv6)

The addresses include a 40-bit pseudorandom number that minimizes the risk of

address collisions if sites merge or packets are misrouted.

Early designs (RFC 3513) used a different block for this purpose (fec0::), dubbed

site-local addresses. However, the definition of what constituted sites remained

unclear and the poorly defined addressing policy created ambiguities for routing.

The address range specification was abandoned and must no longer be used in

new systems.

Addresses starting with fe80: — called link-local addresses — are assigned only in

the local link area. The addresses are generated usually automatically by the

operating system's IP layer for each network interface. This provides instant

automatic network connectivity for any IPv6 host and means that if several hosts

connect to a common hub or switch, they have an instant communication path via

their link-local IPv6 address. This feature is used extensively, and invisibly to most

users, in the lower layers of IPv6 network administration (cf. Neighbor Discovery

Protocol).

None of the private address prefixes may be routed in the public Internet.

IP subnetworks

Main article: Subnetwork

The technique of subnetting can operate in both IPv4 and IPv6 networks. The IP

address is divided into two parts: the network address and thehost identifier.

The subnet mask (in IPv4 only) or the CIDR prefix determines how the IP address is

divided into network and host parts.

The term subnet mask is only used within IPv4. Both IP versions however use

the Classless Inter-Domain Routing (CIDR) concept and notation. In this, the IP

address is followed by a slash and the number (in decimal) of bits used for the

network part, also called the routing prefix. For example, an IPv4 address and its

subnet mask may be 192.0.2.1 and 255.255.255.0, respectively. The CIDR

notation for the same IP address and subnet is 192.0.2.1/24, because the first 24

bits of the IP address indicate the network and subnet.

Static and dynamic IP addresses

When a computer is configured to use the same IP address each time it powers up,

this is known as a Static IP address. In contrast, in situations when the computer's

IP address is assigned automatically, it is known as a Dynamic IP address.

Method of assignment

Static IP addresses are manually assigned to a computer by an administrator. The

exact procedure varies according to platform. This contrasts with dynamic IP

addresses, which are assigned either by the computer interface or host software

itself, as in Zeroconf, or assigned by a server using Dynamic Host Configuration

Protocol (DHCP). Even though IP addresses assigned using DHCP may stay the

same for long periods of time, they can generally change. In some cases, a network

administrator may implement dynamically assigned static IP addresses. In this

case, a DHCP server is used, but it is specifically configured to always assign the

same IP address to a particular computer. This allows static IP addresses to be

configured centrally, without having to specifically configure each computer on the

network in a manual procedure.

In the absence or failure of static or stateful (DHCP) address configurations, an

operating system may assign an IP address to a network interface using state-less

autoconfiguration methods, such as Zeroconf.

Uses of dynamic addressing

Dynamic IP addresses are most frequently assigned on LANs and broadband

networks by Dynamic Host Configuration Protocol (DHCP) servers. They are used

because it avoids the administrative burden of assigning specific static addresses to

each device on a network. It also allows many devices to share limited address

space on a network if only some of them will be online at a particular time. In most

current desktop operating systems, dynamic IP configuration is enabled by default

so that a user does not need to manually enter any settings to connect to a network

with a DHCP server. DHCP is not the only technology used to assigning dynamic IP

addresses. Dialup and some broadband networks use dynamic address features of

the Point-to-Point Protocol.

Sticky dynamic IP address

A sticky dynamic IP address or sticky IP is an informal term used by cable and DSL

Internet access subscribers to describe a dynamically assigned IP address that

does not change often. The addresses are usually assigned with the DHCP

protocol. Since the modems are usually powered-on for extended periods of time,

the address leases are usually set to long periods and simply renewed upon

expiration. If a modem is turned off and powered up again before the next expiration

of the address lease, it will most likely receive the same IP address.

Address autoconfiguration

RFC 3330 defines an address block, 169.254.0.0/16, for the special use in link-local

addressing for IPv4 networks. In IPv6, every interface, whether using static or

dynamic address assignments, also receives a local-link address automatically in

the fe80::/10 subnet.

These addresses are only valid on the link, such as a local network segment or

point-to-point connection, that a host is connected to. These addresses are not

routable and like private addresses cannot be the source or destination of packets

traversing the Internet.

When the link-local IPv4 address block was reserved, no standards existed for

mechanisms of address autoconfiguration. Filling the void,Microsoft created an

implementation that called Automatic Private IP Addressing (APIPA). Due to

Microsoft's market power, APIPA has been deployed on millions of machines and

has, thus, become a de facto standard in the industry. Many years later,

the IETF defined a formal standard for this functionality, RFC 3927,

entitled Dynamic Configuration of IPv4 Link-Local Addresses.

Uses of static addressing

Some infrastructure situations have to use static addressing, such as when finding

the Domain Name System host that will translate domain names to IP addresses.

Static addresses are also convenient, but not absolutely necessary, to locate

servers inside an enterprise. An address obtained from a DNS server comes with

a time to live, or caching time, after which it should be looked up to confirm that it

has not changed. Even static IP addresses do change as a result of network

administration (RFC 2072)

Modifications to IP addressing

IP blocking and firewalls

Main articles: IP blocking and Firewall

Firewalls are common on today's Internet. For increased network security, they

control access to private networks based on the public IP of the client. Whether

using a blacklist or a whitelist, the IP address that is blocked is the perceived public

IP address of the client, meaning that if the client is using a proxy server or NAT,

blocking one IP address might block many individual people.

IP address translation

Main article: Network Address Translation

Multiple client devices can appear to share IP addresses: either because they are

part of a shared hosting web server environment or because an IPv4 network

address translator (NAT) or proxy server acts as an intermediary agent on behalf of

its customers, in which case the real originating IP addresses might be hidden from

the server receiving a request. A common practice is to have a NAT hide a large

number of IP addresses in a private network. Only the "outside" interface(s) of the

NAT need to have Internet-routable addresses[5].

Most commonly, the NAT device maps TCP or UDP port numbers on the outside to

individual private addresses on the inside. Just as a telephone number may have

site-specific extensions, the port numbers are site-specific extensions to an IP

address.

In small home networks, NAT functions usually take place in a residential

gateway device, typically one marketed as a "router". In this scenario, the

computers connected to the router would have 'private' IP addresses and the router

would have a 'public' address to communicate with the Internet. This type of router

allows several computers to share one public IP address.

Ethernet hub

A network hub or repeater hub is a device for connecting multiple twisted

pair orfiber optic Ethernet devices together and thus making them act as a

single network segment. Hubs work at the physical layer (layer 1) of the OSI model.

The device is thus a form of multiport repeater. Repeater hubs also participate in

collision detection, forwarding a jam signal to all ports if it detects a collision.

Hubs also often come with a BNC and/or AUI connector to allow connection to

legacy10BASE2 or 10BASE5 network segments. The availability of low-

priced network switches has largely rendered hubs obsolete but they are still seen

in older installations and more specialized applications.

.4-port Ethernet hub

Technical information

A network hub is a fairly unsophisticated broadcast device. Hubs do not manage

any of the traffic that comes through them, and any packet entering any port is

broadcast out on all other ports. Since every packet is being sent out through all

other ports, packet collisions result—which greatly impedes the smooth flow of

traffic.

The need for hosts to be able to detect collisions limits the number of hubs and the

total size of the network. For 10 Mbit/s networks, up to 5 segments (4 hubs) are

allowed between any two end stations. For 100 Mbit/s networks, the limit is reduced

to 3 segments (2 hubs) between any two end stations, and even that is only allowed

if the hubs are of the low delay variety. Some hubs have special (and generally

manufacturer specific) stack ports allowing them to be combined in a way that

allows more hubs than simple chaining through Ethernet cables, but even so, a

large Fast Ethernet network is likely to require switches to avoid the chaining limits

of hubs.

Most hubs (intelligent hubs) detect typical problems, such as excessive collisions on

individual ports, and partition the port, disconnecting it from the shared medium.

Thus, hub-based Ethernet is generally more robust than coaxial cable-based

Ethernet, where a misbehaving device can disable the entire collision domain. Even

if not partitioned automatically, an intelligent hub makes troubleshooting easier

because status lights can indicate the possible problem source or, as a last resort,

devices can be disconnected from a hub one at a time much more easily than a

coaxial cable. They also remove the need to troubleshoot faults on a huge cable

with multiple taps.

Hubs classify as Layer 1 devices in the OSI model. At the physical layer, hubs can

support little in the way of sophisticated networking. Hubs do not read any of the

data passing through them and are not aware of their source or destination.

Essentially, a hub simply receives incoming packets, possibly amplifies the

electrical signal, and broadcasts these packets out to all devices on the network -

including the one that originally sent the packet.

Technically speaking, three different types of hubs exist:

1. Passive (A hub which does not need an external power source, because it does

not regenerate the signal and therefore falls as part of the cable, with respect to

maximum cable lengths)

2. Active (A hub which regenerates the signal and therefore needs an external

power supply)

3. Intelligent (A hub which provides error detection (e.g. excessive collisions) and

also does what an active hub does)

Passive hubs do not amplify the electrical signal of incoming packets before

broadcasting them out to the network. Active hubs, on the other hand, do perform

this amplification, as does a different type of dedicated network device called a

repeater. Another, not so common, name for the term concentrator is referring to a

passive hub and the term multiport repeater is referred to an active hub.

Intelligent hubs add extra features to an active hub that are of particular importance

to businesses. An intelligent hub typically is stackable (built in such a way that

multiple units can be placed one on top of the other to conserve space). It also

typically includes remote management capabilities via Simple Network Management

Protocol (SNMP) and virtual LAN (VLAN) support.

Uses

Historically, the main reason for purchasing hubs rather than switches was their

price. This has largely been eliminated by reductions in the price of switches, but

hubs can still be useful in special circumstances:

For inserting a protocol analyzer into a network connection, a hub is an

alternative to a network tap or port mirroring.

Some computer clusters require each member computer to receive all of

the traffic going to the cluster.[citation needed] A hub will do this naturally; using a

switch requires special configuration.

When a switch is accessible for end users to make connections, for

example, in a conference room, an inexperienced or careless user (orsaboteur)

can bring down the network by connecting two ports together, causing a loop.

This can be prevented by using a hub, where a loop will break other users on

the hub, but not the rest of the network. (It can also be prevented by buying

switches that can detect and deal with loops, for example by implementing

the Spanning Tree Protocol.)

A hub with a 10BASE2 port can be used to connect devices that only

support 10BASE2 to a modern network. The same goes for linking in an

old thicknet network segment using an AUI port on a hub (individual devices

that were intended for thicknet can be linked to modern Ethernet by using an

AUI-10BASE-T transceiver).

Network switch

A network switch is a computer networking device that connects network

segments.

The term commonly refers to a network bridge that processes and routes data at

the data link layer (layer 2) of the OSI model. Switches that additionally process

data at the network layer(layer 3 and above) are often referred to as Layer 3

switches or multilayer switches.

The term network switch does not generally encompass unintelligent or passive

network devices such as hubs and repeaters. The first Ethernet switch was

introduced by Kalpana in 1990.[1]

Typical SOHO network switch.

Back view of Atlantis network switch withEthernet ports.

Function

The network switch, packet switch (or just switch) plays an integral part in

most Ethernet local area networks or LANs. Mid-to-large sized LANs contain a

number of linked managed switches. Small office/home office (SOHO) applications

typically use a single switch, or an all-purposeconverged device such

as gateway access to small office/home broadband services such as DSL

router or cable Wi-Fi router. In most of these cases, the end user device contains

a router and components that interface to the particular physical broadband

technology, as in the Linksys 8-port and 48-port devices. User devices may also

include a telephone interface to VoIP.

In the context of a standard 10/100 Ethernet switch, a switch operates at the data-

link layer of the OSI model to create a different collision domain per switch port. If

you have 4 computers A/B/C/D on 4 switch ports, then A and B can transfer data

between them as well as C and D at the same time, and they will never interfere

with each others' conversations. In the case of a "hub" then they would all have to

share the bandwidth, run in Half duplex and there would be collisions and

retransmissions. Using a switch is called micro-segmentation. It allows you to have

dedicated bandwidth on point to point connections with every computer and to

therefore run in Full duplex with no collisions.

Role of switches in networks

Network switch is a marketing term rather than a technical one.[citation needed] Switches

may operate at one or more OSI layers, includingphysical, data link, network,

or transport (i.e., end-to-end). A device that operates simultaneously at more than

one of these layers is called amultilayer switch, although use of the term is

diminishing.[citation needed]

In switches intended for commercial use, built-in or modular interfaces make it

possible to connect different types of networks, includingEthernet, Fibre

Channel, ATM, ITU-T G.hn and 802.11. This connectivity can be at any of the layers

mentioned. While Layer 2 functionality is adequate for speed-shifting within one

technology, interconnecting technologies such as Ethernet and token ring are easier

at Layer 3.

Interconnection of different Layer 3 networks is done by routers. If there are any

features that characterize "Layer-3 switches" as opposed to general-purpose

routers, it tends to be that they are optimized, in larger switches, for high-density

Ethernet connectivity.

In some service provider and other environments where there is a need for a great

deal of analysis of network performance and security, switches may be connected

between WAN routers as places for analytic modules. Some vendors

provide firewall,[2][3] network intrusion detection,[4] and performance analysis modules

that can plug into switch ports. Some of these functions may be on combined

modules.[5]

In other cases, the switch is used to create a mirror image of data that can go to an

external device. Since most switch port mirroring provides only one mirrored

stream, network hubs can be useful for fanning out data to several read-only

analyzers, such as intrusion detection systemsand packet sniffers.

Layer-specific functionality

A modular network switch with three network modules (a total of 24 Ethernet and 14 Fast Ethernet

ports) and one power supply.

While switches may learn about topologies at many layers, and forward at one or

more layers, they do tend to have common features. Other than for high-

performance applications, modern commercial switches use primarily Ethernet

interfaces, which can have different input and output speeds of 10, 100, 1000 or

10,000 megabits per second. Switch ports almost always default to Full

duplex operation, unless there is a requirement for interoperability with devices that

are strictly Half duplex. Half duplex means that the device can only send or receive

at any given time, whereas Full duplex can send and receive at the same time.

At any layer, a modern switch may implement power over Ethernet (PoE), which

avoids the need for attached devices, such as an IP telephone or wireless access

point, to have a separate power supply. Since switches can have redundant power

circuits connected touninterruptible power supplies, the connected device can

continue operating even when regular office power fails.

Layer-1 hubs versus higher-layer switches

A network hub, or repeater, is a fairly unsophisticated network device. Hubs do not

manage any of the traffic that comes through them. Any packet entering a port is

broadcast out or "repeated" on every other port, except for the port of entry. Since

every packet is repeated on every other port, packet collisions result, which slows

down the network.

There are specialized applications where a hub can be useful, such as copying

traffic to multiple network sensors. High end switches have a feature which does the

same thing called port mirroring. There is no longer any significant price difference

between a hub and a low-end switch.[6]

Layer 2

A network bridge, operating at the Media Access Control (MAC) sublayer of the

data link layer, may interconnect a small number of devices in a home or office. This

is a trivial case of bridging, in which the bridge learns the MAC address of each

connected device. Single bridges also can provide extremely high performance in

specialized applications such as storage area networks.

Classic bridges may also interconnect using a spanning tree protocol that disables

links so that the resulting local area network is a treewithout loops. In contrast to

routers, spanning tree bridges must have topologies with only one active path

between two points. The older IEEE 802.1D spanning tree protocol could be quite

slow, with forwarding stopping for 30 seconds while the spanning tree would

reconverge. A Rapid Spanning Tree Protocol was introduced as IEEE 802.1w, but

the newest edition of IEEE 802.1D-2004, adopts the 802.1w extensions as the base

standard. The IETF is specifying the TRILL protocol, which is the application of link-

state routing technology to the layer-2 bridging problem. Devices which implement

TRILL, called RBridges, combine the best features of both routers and bridges.

While "layer 2 switch" remains more of a marketing term than a technical term,[citation

needed] the products that were introduced as "switches" tended to

use microsegmentation and Full duplex to prevent collisions among devices

connected to Ethernets. By using an internal forwarding plane much faster than any

interface, they give the impression of simultaneous paths among multiple devices.

Once a bridge learns the topology through a spanning tree protocol, it forwards data

link layer frames using a layer 2 forwarding method. There are four forwarding

methods a bridge can use, of which the second through fourth method were

performance-increasing methods when used on "switch" products with the same

input and output port speeds:

1. Store and forward : The switch buffers and, typically, performs

a checksum on each frame before forwarding it on.

2. Cut through : The switch reads only up to the frame's hardware address

before starting to forward it. There is no error checking with this method.

3. Fragment free : A method that attempts to retain the benefits of both "store

and forward" and "cut through". Fragment free checks the first 64 bytes of

the frame, where addressing information is stored. According to Ethernet

specifications, collisions should be detected during the first 64 bytes of the

frame, so frames that are in error because of a collision will not be

forwarded. This way the frame will always reach its intended destination.

Error checking of the actual data in the packet is left for the end device in

Layer 3 or Layer 4 (OSI), typically a router.

4. Adaptive switching : A method of automatically switching between the other

three modes.

Cut-through switches have to fall back to store and forward if the outgoing port is

busy at the time the packet arrives. While there are specialized applications, such

as storage area networks, where the input and output interfaces are the same

speed, this is rarely the case in general LAN applications. In LANs, a switch used

for end user access typically concentrates lower speed (e.g., 10/100 Mbit/s) into a

higher speed (at least 1 Gbit/s). Alternatively, a switch that provides access to

server ports usually connects to them at a much higher speed than is used by end

user devices.

Layer 3

Within the confines of the Ethernet physical layer, a layer 3 switch can perform

some or all of the functions normally performed by a router. A true router is able to

forward traffic from one type of network connection (e.g., T1, DSL) to another (e.g.,

Ethernet, WiFi).

The most common layer-3 capability is awareness of IP multicast. With this

awareness, a layer-3 switch can increase efficiency by delivering the traffic of a

multicast group only to ports where the attached device has signaled that it wants to

listen to that group. If a switch is not aware of multicasting and broadcasting, frames

are also forwarded on all ports of each broadcast domain, but in the case of IP

multicast this causes inefficient use of bandwidth. To work around this problem

some switches implement IGMP snooping.[7]

Layer 4

While the exact meaning of the term Layer-4 switch is vendor-dependent, it almost

always starts with a capability for network address translation, but then adds some

type of load distribution based on TCP sessions.[8]

The device may include a stateful firewall, a VPN concentrator, or be

an IPSec security gateway.

Layer 7

Layer 7 switches may distribute loads based on URL or by some installation-specific

technique to recognize application-level transactions. A Layer-7 switch may include

a web cache and participate in a content delivery network.[9]

Rack-mounted 24-port 3Com switch

Types of switches

Form factor

Desktop, not mounted in an enclosure, typically intended to be used in a

home or office environment outside of a wiring closet

Rack  mounted

Chassis  — with swappable "switch module" cards. e.g. Alcatel's

OmniSwitch 7000; CiscoCatalyst switch 4500 and 6500; 3Com 7700, 7900E,

8800.

Configuration options

Unmanaged switches — These switches have no configuration interface or

options. They are plug and play. They are typically the least expensive

switches, found in home, SOHO, or small businesses. They can be desktop or

rack mounted.

Managed switches — These switches have one or more methods to modify

the operation of the switch. Common management methods include: a serial

console or command line interface accessed via telnet or Secure Shell, an

embedded Simple Network Management Protocol (SNMP) agent allowing

management from a remote console or management station, or a web interface

for management from a web browser. Examples of configuration changes that

one can do from a managed switch include: enable features such as Spanning

Tree Protocol, set port speed, create or modify Virtual LANs (VLANs), etc. Two

sub-classes of managed switches are marketed today:

Smart (or intelligent) switches — These are managed switches with

a limited set of management features. Likewise "web-managed" switches

are switches which fall in a market niche between unmanaged and

managed. For a price much lower than a fully managed switch they provide

a web interface (and usually no CLI access) and allow configuration of

basic settings, such as VLANs, port-speed and duplex.[10]

Enterprise Managed (or fully managed) switches — These have a

full set of management features, including Command Line Interface, SNMP

agent, and web interface. They may have additional features to manipulate

configurations, such as the ability to display, modify, backup and restore

configurations. Compared with smart switches, enterprise switches have

more features that can be customized or optimized, and are generally more

expensive than "smart" switches. Enterprise switches are typically found in

networks with larger number of switches and connections, where

centralized management is a significant savings in administrative time and

effort. Astackable switch is a version of enterprise-managed switch.

Traffic monitoring on a switched network

Unless port mirroring or other methods such as RMON or SMON are implemented

in a switch,[11] it is difficult to monitor traffic that is bridged using a switch because all

ports are isolated until one transmits data, and even then only the sending and

receiving ports can see the traffic. These monitoring features rarely are present on

consumer-grade switches.

Two popular methods that are specifically designed to allow a network analyst to

monitor traffic are:

Port mirroring  — the switch sends a copy of network packets to a

monitoring network connection.

SMON  — "Switch Monitoring" is described by RFC 2613 and is a protocol

for controlling facilities such as port mirroring.

Another method to monitor may be to connect a Layer-1 hub between the monitored

device and its switch port. This will induce minor delay, but will provide multiple

interfaces that can be used to monitor the individual switch port.

Typical switch management features

Linksys 48-port switch

A rack-mounted switch with network cables

Turn some particular port range on or off

Link speed and duplex settings

Priority settings for ports

MAC filtering  and other types of "port security" features which prevent MAC

flooding

Use of Spanning Tree Protocol

SNMP  monitoring of device and link health

Port mirroring  (also known as: port monitoring, spanning port, SPAN port,

roving analysis port or link mode port)

Link aggregation  (also known as bonding, trunking or teaming)

VLAN settings

802.1X  network access control

IGMP snooping

Link aggregation allows the use of multiple ports for the same connection achieving

higher data transfer speeds. Creating VLANs can serve security and performance

goals by reducing the size of the broadcast domain.

Local area network

"LAN" redirects here. For other uses, see LAN (disambiguation).

A local area network (LAN) is a computer network covering a small physical area,

like a home, office, or small group of buildings, such as a school, or an airport. The

defining characteristics of LANs, in contrast to wide-area networks (WANs), include

their usually higher data-transfer rates, smaller geographic area, and lack of a need

for leased telecommunication lines.

ARCNET, Token Ring and many other technologies have been used in the past,

and G.hn may be used in the future, but Ethernet over twisted pair cabling, and Wi-

Fi are the two most common technologies currently in use.

History

As larger universities and research labs obtained more computers during the late

1960s, there was increasing pressure to provide high-speed interconnections. A

report in 1970 from the Lawrence Radiation Laboratory detailing the growth of their

"Octopus" network[1][2] gives a good indication of the situation.

Cambridge Ring was developed at Cambridge University in 1974[3] but was never

developed into a successful commercial product.

Ethernet was developed at Xerox PARC in 1973–1975,[4] and filed as U.S. Patent

4,063,220. In 1976, after the system was deployed at PARC, Metcalfe and Boggs

published their seminal paper, "Ethernet: Distributed Packet-Switching For Local

Computer Networks."[5]

ARCNET was developed by Datapoint Corporation in 1976 and announced in 1977.

[6] It had the first commercial installation in December 1977 at Chase Manhattan

Bank in New York.[7]

Standards evolution

The development and proliferation of CP/M-based personal computers from the late

1970s and then DOS-based personal computers from 1981 meant that a single site

began to have dozens or even hundreds of computers. The initial attraction of

networking these was generally to share disk space and laser printers, which were

both very expensive at the time. There was much enthusiasm for the concept and

for several years, from about 1983 onward, computer industry pundits would

regularly declare the coming year to be “the year of the LAN”.

In practice, the concept was marred by proliferation of incompatible physical

Layer and network protocol implementations, and a plethora of methods of sharing

resources. Typically, each vendor would have its own type of network card, cabling,

protocol, and network operating system. A solution appeared with the advent

of Novell NetWare which provided even-handed support for dozens of competing

card/cable types, and a much more sophisticated operating system than most of its

competitors. Netware dominated[8] the personal computer LAN business from early

after its introduction in 1983 until the mid 1990s when Microsoft

introduced Windows NT Advanced Server and Windows for Workgroups.

Of the competitors to NetWare, only Banyan Vines had comparable technical

strengths, but Banyan never gained a secure base. Microsoft and3Com worked

together to create a simple network operating system which formed the base of

3Com's 3+Share, Microsoft's LAN Manager and IBM's LAN Server. None of these

were particularly successful.

In this same timeframe, Unix computer workstations from vendors such as Sun

Microsystems, Hewlett-Packard, Silicon Graphics, Intergraph,NeXT and Apollo were

using TCP/IP based networking. Although this market segment is now much

reduced, the technologies developed in this area continue to be influential on the

Internet and in both Linux and Apple Mac OS X networking—and the TCP/IP

protocol has now almost completely replaced IPX, AppleTalk, NBF and other

protocols used by the early PC LANs.

Cabling

Early LAN cabling had always been based on various grades of co-axial cable, but

IBM's Token Ring used shielded twisted pair cabling of their own design, and in

1984 StarLAN showed the potential of simple Cat3 unshielded twisted pair—the

same simple cable used for telephone systems. This led to the development

of 10Base-T (and its successors) and structured cabling which is still the basis of

most LANs today. In addition, fiber-optic cabling is increasingly used.

Technical aspects

Switched Ethernet is the most common Data Link Layer implementation on local

area networks. At the Network Layer, the Internet Protocol has become the

standard. However, many different options have been used in the history of LAN

development and some continue to be popular in niche applications. Smaller LANs

generally consist of one or more switches linked to each other—often at least one is

connected to a router,cable modem, or ADSL modem for Internet access.

Larger LANs are characterized by their use of redundant links with switches using

the spanning tree protocol to prevent loops, their ability to manage differing traffic

types via quality of service (QoS), and to segregate traffic with VLANs. Larger LANS

also contain a wide variety of network devices such as switches, firewalls, routers,

load balancers, and sensors.[9]

LANs may have connections with other LANs via leased lines, leased services, or

by tunneling across the Internet using virtual private networktechnologies.

Depending on how the connections are established and secured in a LAN, and the

distance involved, a LAN may also be classified as metropolitan area

network (MAN) or wide area networks (WAN).

LAN switchingThis article addresses packet switching in computer networks.

LAN switching is a form of packet switching used in local area networks. Switching

technologies are crucial to network design, as they allow traffic to be sent only

where it is needed in most cases, using fast, hardware-based methods.

Layer 2 switching

Layer 2 switching is hardware based, which means it uses the media access control

address (MAC address) from the host's network interface cards (NICs) to decide

where to forward frames. Switches use application-specific integrated

circuits (ASICs) to build and maintain filter tables (also known as MAC address

tables). One way to think of a layer 2 switch is as a multiport bridge.

Layer 2 switching provides the following

Hardware-based bridging (MAC)

Wire speed

High speed

Low latency

Low cost

Layer 2 switching is highly efficient because there is no modification to the data

packet, only to the frame encapsulation of the packet, and only when the data

packet is passing through dissimilar media (such as from Ethernet to FDDI). Layer 2

switching is used for workgroup connectivity and network segmentation (breaking

up collision domains). This allows a flatter network design with more network

segments than traditional10BaseT shared networks. Layer 2 switching has helped

develop new components in the network infrastructure

Server farms  — Servers are no longer distributed to physical locations

because virtual LANs can be created to create broadcast domains in a switched

internetwork. This means that all servers can be placed in a central location, yet

a certain server can still be part of a workgroup in a remote branch, for

example.

Intranets  — Allows organization-wide client/server communications based

on a Web technology.

These new technologies allow more data to flow off from local subnets and onto a

routed network, where a router's performance can become the bottleneck.

Limitations

Layer 2 switches have the same limitations as bridge networks. Remember that

bridges are good if a network is designed by the 80/20 rule: users spend 80 percent

of their time on their local segment.

Bridged networks break up collision domains, but the network remains one

large broadcast domain. Similarly, layer 2 switches (bridges) cannot break up

broadcast domains, which can cause performance issues and limits the size of your

network. Broadcast and multicasts, along with the slow convergence of spanning

tree, can cause major problems as the network grows. Because of these problems,

layer 2 switches cannot completely replace routers in the internetwork.

Layer 3 switching

The only difference between a layer 3 switch and router is the way the administrator

creates the physical implementation. Also, traditional routers use microprocessors

to make forwarding decisions, and the switch performs only hardware-based packet

switching. However, some traditional routers can have other hardware functions as

well in some of the higher-end models. Layer 3 switches can be placed anywhere in

the network because they handle high-performance LAN traffic and can cost-

effectively replace routers. Layer 3 switching is all hardware-based packet

forwarding, and all packet forwarding is handled by hardware ASICs. Layer 3

switches really are no different functionally than a traditional router and perform the

same functions, which are listed here

Determine paths based on logical addressing

Run layer 3 checksums (on header only)

Use Time to Live (TTL)

Process and respond to any option information

Update Simple Network Management Protocol (SNMP) managers

with Management Information Base (MIB) information

Provide Security

The benefits of layer 3 switching include the following

Hardware-based packet forwarding

High-performance packet switching

High-speed scalability

Low latency

Lower per-port cost

Flow accounting

Security

Quality of service  (QoS)

Layer 4 switching

Layer 4 switching is considered a hardware-based layer 3 switching technology that

can also consider the application used (for example, Telnet or FTP).

Layer 4 switching provides additional routing above layer 3 by using the port

numbers found in the Transport layer header to make routing decisions.

These port numbers are found in Request for Comments (RFC) 1700 and reference

the upper-layer protocol, program, or application.

Layer 4 information has been used to help make routing decisions for quite a while.

For example, extended access lists can filter packets based on layer 4 port

numbers. Another example is accounting information gathered by NetFlow

switching in Cisco's higher-end routers.

The largest benefit of layer 4 switching is that the network administrator can

configure a layer 4 switch to prioritize data traffic by application, which means a

QoS can be defined for each user.

For example, a number of users can be defined as a Video group and be assigned

more priority, or band-width, based on the need for video conferencing.

Multi-layer switching (MLS)

Main article: Multilayer switch

Multi-layer switching combines layer 2, 3, and 4 switching technologies and

provides high-speed scalability with low latency. It accomplishes this high

combination of high-speed scalability with low latency by using huge filter tables

based on the criteria designed by the network administrator.

Multi-layer switching can move traffic at wire speed and also provide layer 3 routing,

which can remove the bottleneck from the network routers. This technology is

based on the idea of "route once, switch many".

Multi-layer switching can make routing/switching decisions based on the following

MAC source/destination address in a Data Link frame

IP source/destination address in the Network layer header

Protocol field in the Network layer header

Port source/destination numbers in the Transport layer header

There is no performance difference between a layer 3 and a layer 4 switch because

the routing/switching is all hardware based.

RouterA router, pronounced / ˈra ʊ tər/  in the United States, Canada, and Australia,

and / ˈruːt ər/  in the UK andIreland (to differentiate it from the tool used to rout wood),

is an electronic device used to connect two or more computers or other electronic

devices to each other, and usually to the Internet, by wire or radiosignals. This

allows several computers to communicate with each other and to the Internet at the

same time. If wires are used, each computer is connected by its own wire to the

router. Modern wired-only routers designed for the home or small business typically

have one "input" port (to the Internet) and four "output" ports, one or more of which

can be connected to other computers. A typical modern home wireless router, in

addition to having four wired ports, also allows several devices to connect with it

wirelessly. Most modernpersonal computers are built with a wired port (almost

always an Ethernet type), which allows them to connect to a router with the addition

of just a cable (typically a Category 5e type). To connect with a wireless router, a

device must have an adapter. This is sometimes, but not always, included with the

computer at manufacture. Some electronic games, including handheld electronic

games, have an adapter built-in, or one can be added later.

More technically, a router is a networking device whose software and hardware are

usually tailored to the tasks of routing and forwarding information. Routers connect

two or more logical subnets, which do not necessarily map one-to-one to the

physical interfaces of the router.[1] The term "layer 3 switching" is often used

interchangeably with routing, but switch is a general term without a rigorous

technical definition. In marketing usage, a switch is generally optimized

for Ethernet LAN interfaces and may not have other physical interface types. In

comparison, the network hub (predecessor of the "switch" or "switching hub") does

not do any routing, instead every packet it receives on one network line gets

forwarded to all the other network lines.

Routers operate in two different planes:[2]

Control plane , in which the router learns the outgoing interface that is most

appropriate for forwarding specific packets to specific destinations,

Forwarding plane , which is responsible for the actual process of sending a

packet received on a logical interface to an outbound logical interface.

Cisco 1800 Router

Nortel ERS 8600

For the pure Internet Protocol (IP) forwarding function, router design tries to

minimize the state information kept on individual packets. Once a packet is

forwarded, the router should no longer retain statistical information about it. It is the

sending and receiving endpoints that keeps information about such things as

errored or missing packets.

Forwarding decisions can involve decisions at layers other than the IP internetwork

layer or OSI layer 3. Again, the marketing term switch can be applied to devices that

have these capabilities. A function that forwards based on data link layer, or OSI

layer 2, information, is properly called a bridge. Marketing literature may call it a

layer 2 switch, but a switch has no precise definition.

Among the most important forwarding decisions is deciding what to do when

congestion occurs, i.e., packets arrive at the router at a rate higher than the router

can process. Three policies commonly used in the Internet are Tail drop, Random

early detection, and Weighted random early detection. Tail drop is the simplest and

most easily implemented; the router simply drops packets once the length of the

queue exceeds the size of the buffers in the router. Random early detection (RED)

probabilistically drops datagrams early when the queue exceeds a configured size.

Weighted random early detection requires a weighted average queue size to

exceed the configured size, so that short bursts will not trigger random drops.

A router uses a routing table to decide where the packet should be sent so if the

router cant find the preferred address then it will look down the routing table and

decide which is the next best address to send it to.

Types of routers

Routers may provide connectivity inside enterprises, between enterprises and the

Internet, and inside Internet Service Providers (ISPs). The largest routers (for

example the Cisco CRS-1 or Juniper T1600) interconnect ISPs, are used inside

ISPs, or may be used in very large enterprise networks. The smallest routers

provide connectivity for small and home offices.

Routers for Internet connectivity and internal use

Routers intended for ISP and major enterprise connectivity will almost invariably

exchange routing information with the Border Gateway Protocol (BGP). RFC

4098 [3]  defines several types of BGP-speaking routers:

Edge Router: Placed at the edge of an ISP network, it speaks

external BGP (eBGP) to a BGP speaker in another provider or large

enterprise Autonomous System(AS).

Subscriber Edge Router: Located at the edge of the subscriber's network, it

speaks eBGP to its provider's AS(s). It belongs to an end user (enterprise)

organization.

Inter-provider Border Router: Interconnecting ISPs, this is a BGP speaking

router that maintains BGP sessions with other BGP speaking routers in other

providers' ASes.

Core router: A router that resides within the middle or backbone of the LAN

network rather than at its periphery.

Within an ISP: Internal to the provider's AS, such a router speaks internal

BGP (iBGP) to that provider's edge routers, other intra-provider core

routers, or the provider's inter-provider border routers.

"Internet backbone:" The Internet does not have a clearly identifiable

backbone, as did its predecessors. See default-free zone (DFZ).

Nevertheless, it is the major ISPs' routers that make up what many would

consider the core. These ISPs operate all four types of the BGP-speaking

routers described here. In ISP usage, a "core" router is internal to an ISP,

and used to interconnect its edge and border routers. Core routers may

also have specialized functions in virtual private networks based on a

combination of BGP and Multi-Protocol Label Switching (MPLS).[4]

Routers are also used for port forwarding for private servers.

Small Office Home Office (SOHO) connectivity

Main article: Residential gateway

Residential gateways (often called routers) are frequently used in homes to

connect to a broadband service, such as IP over cable or DSL. Such a router

may also include an internal DSL modem. Residential gateways and SOHO

routers typically provide network address translationand port address

translation in addition to routing. Instead of directly presenting the IP

addresses of local computers to the remote network, such a residential

gateway makes multiple local computers appear to be a single computer.

SOHO routers may also support Virtual Private Network tunnel functionality to

provide connectivity to an enterprise network..

Enterprise routers

All sizes of routers may be found inside enterprises. The most powerful routers

tend to be found in ISPs and academic & research facilities. Large businesses

may also need powerful routers.

A three-layer model is in common use, not all of which need be present in

smaller networks.[5]

Access

Access routers, including SOHO, are located at customer sites such as branch

offices that do not need hierarchical routing of their own. Typically, they are

optimized for low cost.

Distribution

Distribution routers aggregate traffic from multiple access routers, either at the

same site, or to collect the data streams from multiple sites to a major

enterprise location. Distribution routers often are responsible for enforcing

quality of service across a WAN, so they may have considerable memory,

multiple WAN interfaces, and substantial processing intelligence.

They may also provide connectivity to groups of servers or to external

networks. In the latter application, the router's functionality must be carefully

considered as part of the overall security architecture. Separate from the

router may be a Firewalled or VPN concentrator, or the router may include

these and other security functions.

When an enterprise is primarily on one campus, there may not be a distinct

distribution tier, other than perhaps off-campus access. In such cases, the

access routers, connected to LANs, interconnect via core routers.

Core

In enterprises, a core router may provide a "collapsed backbone"

interconnecting the distribution tier routers from multiple buildings of a

campus, or large enterprise locations. They tend to be optimized for high

bandwidth.

When an enterprise is widely distributed with no central location(s), the

function of core routing may be subsumed by the WAN service to which the

enterprise subscribes, and the distribution routers become the highest tier.

History

Leonard Kleinrock and the first IMP.

A Cisco ASM/2-32EM router deployed at CERN in 1987.

The very first device that had fundamentally the same functionality as a router

does today, i.e a packet switch, was the Interface Message Processor (IMP);

IMPs were the devices that made up the ARPANET, the first packet

switching network. The idea for a router (although they were called "gateways"

at the time) initially came about through an international group of computer

networking researchers called the International Network Working Group

(INWG). Set up in 1972 as an informal group to consider the technical issues

involved in connecting different networks, later that year it became a

subcommittee of theInternational Federation for Information Processing. [6]

These devices were different from most previous packet switches in two ways.

First, they connected dissimilar kinds of networks, such as serial

lines and local area networks. Second, they wereconnectionless devices,

which had no role in assuring that traffic was delivered reliably, leaving that

entirely to the hosts (although this particular idea had been previously

pioneered in the CYCLADES network).

The idea was explored in more detail, with the intention to produce a real

prototype system, as part of two contemporaneous programs. One was the

initial DARPA-initiated program, which created the TCP/IParchitecture of

today. [7] The other was a program at Xerox PARC to explore new networking

technologies, which produced the PARC Universal Packet system, although

due to corporate intellectual property concerns it received little attention

outside Xerox until years later. [8]

The earliest Xerox routers came into operation sometime after early 1974. The

first true IP router was developed by Virginia Strazisar at BBN, as part of that

DARPA-initiated effort, during 1975-1976. By the end of 1976, three PDP-11-

based routers were in service in the experimental prototype Internet. [9]

The first multiprotocol routers were independently created by staff researchers

at MIT and Stanford in 1981; the Stanford router was done by William Yeager,

and the MIT one by Noel Chiappa; both were also based on PDP-

11s. [10] [11] [12] [13]

As virtually all networking now uses IP at the network layer, multiprotocol

routers are largely obsolete, although they were important in the early stages

of the growth of computer networking, when several protocols other than

TCP/IP were in widespread use. Routers that handle both IPv4 and IPv6

arguably are multiprotocol, but in a far less variable sense than a router that

processed AppleTalk, DECnet, IP, and Xerox protocols.

In the original era of routing (from the mid-1970s through the 1980s), general-

purpose mini-computers served as routers. Although general-purpose

computers can perform routing, modern high-speed routers are highly

specialized computers, generally with extra hardware added to accelerate both

common routing functions such as packet forwarding and specialised functions

such as IPsec encryption.

Still, there is substantial use of Linux and Unix machines, running open source

routing code, for routing research and selected other applications.

While Cisco's operating system was independently designed, other major

router operating systems, such as those from Juniper Networks and Extreme

Networks, are extensively modified but still have Unix ancestry.