Eee 2520teletraffic Engineering-h1

8/3/2019 Eee 2520teletraffic Engineering-h1

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ETI 2503 TELETRAFFIC ENGINEERING

Course content

System structure: Basic communication system. Types of switching: circuit switching, message

switching and packet switching. Network topologies, inter-exchange signaling. Exchanges:Analogue, Digital, stored program control exchanges, private automatic branch exchange. Calltypes: local, trunk and international, automatic multi-exchange connection and inter-exchangesignaling. Terminal Equipment: Telephone set, telex, facsimile, computer. CommunicationArchitecture, communication protocols, Layer Architecture in data network, Local areanetworks, wide area networks, inter-networking, security. System design and planning: basictraffic theory, queuing theory, grade of service, demand of service, economic analysis andplanning, size and capacity.

1. TELETRAFFIC ENGINEERING

Teletraffic engineering is a method of optimizing the performance of a telecommunicationsnetwork by dynamically analyzing, predicting and regulating the behavior of data transmittedover that network. Teletraffic engineering is also known as traffic engineering and trafficmanagement. The techniques of teletraffic engineering can be applied to networks of all kinds,including the PSTN (public switched telephone network), LANs (local area networks), WANs(wide area networks), cellular telephone networks, proprietary business and the Internet.

TELECOMMUNICATION

Telecommunication is the transmission of information over significant distances tocommunicate. In earlier times, telecommunications involved the use of visual signals, such asbeacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audiomessages via coded drumbeats, lung-blown horns, or sent by loud whistles, for example. In themodern age of electricity and electronics, telecommunications now also includes the use ofelectrical devices such as telegraphs, telephones, and teleprinters, the use of radio and microwavecommunications, as well as fiber optics and their associated electronics, plus the use of the

orbiting satellites and the Internet.

A revolution in wireless telecommunicationsbegan in the first decade of the 20th century withpioneering developments in wireless radio communications by Nikola Tesla and GuglielmoMarconi. Marconi won the Nobel Prize in Physics in 1909 for his efforts. Other highly notablepioneering inventors and developers in the field of electrical and electronic telecommunicationsinclude Charles Wheatstone and Samuel Morse (telegraph), Alexander Graham Bell (telephone),
http://whatis.techtarget.com/definition/0,289893,sid9_gci1262258,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci212644,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci211894,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci214316,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci214117,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci211763,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci212370,00.htmlhttp://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Beaconhttp://en.wikipedia.org/wiki/Smoke_signalhttp://en.wikipedia.org/wiki/Semaphore_linehttp://en.wikipedia.org/wiki/Signal_flaghttp://en.wikipedia.org/wiki/Heliographhttp://en.wikipedia.org/wiki/Electrical_telegraphhttp://en.wikipedia.org/wiki/Teleprinterhttp://en.wikipedia.org/wiki/Microwave_transmissionhttp://en.wikipedia.org/wiki/Microwave_transmissionhttp://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Communications_satellitehttp://en.wikipedia.org/wiki/Wireless_communicationhttp://en.wikipedia.org/wiki/Wirelesshttp://en.wikipedia.org/wiki/Radio_communicationshttp://en.wikipedia.org/wiki/Nikola_Teslahttp://en.wikipedia.org/wiki/Guglielmo_Marconihttp://en.wikipedia.org/wiki/Guglielmo_Marconihttp://en.wikipedia.org/wiki/Nobel_Prize_in_Physicshttp://en.wikipedia.org/wiki/Charles_Wheatstonehttp://en.wikipedia.org/wiki/Samuel_F.B._Morsehttp://en.wikipedia.org/wiki/Alexander_Graham_Bellhttp://whatis.techtarget.com/definition/0,289893,sid9_gci1262258,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci212644,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci211894,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci214316,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci214117,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci211763,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci212370,00.htmlhttp://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Beaconhttp://en.wikipedia.org/wiki/Smoke_signalhttp://en.wikipedia.org/wiki/Semaphore_linehttp://en.wikipedia.org/wiki/Signal_flaghttp://en.wikipedia.org/wiki/Heliographhttp://en.wikipedia.org/wiki/Electrical_telegraphhttp://en.wikipedia.org/wiki/Teleprinterhttp://en.wikipedia.org/wiki/Microwave_transmissionhttp://en.wikipedia.org/wiki/Microwave_transmissionhttp://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Communications_satellitehttp://en.wikipedia.org/wiki/Wireless_communicationhttp://en.wikipedia.org/wiki/Wirelesshttp://en.wikipedia.org/wiki/Radio_communicationshttp://en.wikipedia.org/wiki/Nikola_Teslahttp://en.wikipedia.org/wiki/Guglielmo_Marconihttp://en.wikipedia.org/wiki/Guglielmo_Marconihttp://en.wikipedia.org/wiki/Nobel_Prize_in_Physicshttp://en.wikipedia.org/wiki/Charles_Wheatstonehttp://en.wikipedia.org/wiki/Samuel_F.B._Morsehttp://en.wikipedia.org/wiki/Alexander_Graham_Bell


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Edwin Armstrong, and Lee de Forest (radio), as well as John Logie Baird and Philo Farnsworth(television).

Telecommunications play an important role in the world economy and the worldwidetelecommunication industry's revenue was estimated to be $3.85 trillion in 2008.[1] The service

revenue of the global telecommunications industry was estimated to be $1.7 trillion in 2008, andis expected to touch $2.7 trillion by 2013.

Key concepts

A number of key concepts reoccur throughout the literature on modern telecommunicationsystems. Some of these concepts are discussed below.

Basic elements

A basic telecommunication system consists of three primary units that are always present in

some form:

A transmitterthat takes information and converts it to a signal. A transmission medium, also called the "physical channel" that carries the signal. An

example of this is the "free space channel". A receiver that takes the signal from the channel and converts it back into usable

information.

For example, in a radio broadcasting station the station's largepower amplifieris the transmitter;and the broadcasting antenna is the interface between the power amplifier and the "free spacechannel". The free space channel is the transmission medium; and the receiver's antenna is the

interface between the free space channel and the receiver. Next, the radio receiver is thedestination of the radio signal, and this is where it is converted from electricity to sound forpeople to listen to.

Sometimes, telecommunication systems are "duplex" (two-way systems) with a single box ofelectronics working as both a transmitter and a receiver, or a transceiver. For example, a cellulartelephone is a transceiver. The transmission electronics and the receiver electronics in atransceiver are actually quite independent of each other. This can be readily explained by the factthat radio transmitters contain power amplifiers that operate with electrical powers measured inthe watts or kilowatts, but radio receivers deal with radio powers that are measured in themicrowatts ornanowatts. Hence, transceivers have to be carefully designed and built to isolate

their high-power circuitry and their low-power circuitry from each other.

Telecommunication over telephone lines is called point-to-point communication because it isbetween one transmitter and one receiver. Telecommunication through radio broadcasts is called broadcast communication because it is between one powerful transmitter and numerous low-power but sensitive radio receivers.
http://en.wikipedia.org/wiki/Edwin_Armstronghttp://en.wikipedia.org/wiki/Lee_de_Foresthttp://en.wikipedia.org/wiki/John_Logie_Bairdhttp://en.wikipedia.org/wiki/Philo_Farnsworthhttp://en.wikipedia.org/wiki/Telecommunication#cite_note-plunkettresearch.com-0http://en.wikipedia.org/wiki/Communication_systemhttp://en.wikipedia.org/wiki/Transmitterhttp://en.wikipedia.org/wiki/Signal_(electrical_engineering)http://en.wikipedia.org/wiki/Transmission_mediumhttp://en.wikipedia.org/wiki/Free-space_optical_communicationhttp://en.wikipedia.org/wiki/Receiver_(radio)http://en.wikipedia.org/wiki/Radio_stationhttp://en.wikipedia.org/wiki/Electronic_amplifierhttp://en.wikipedia.org/wiki/Antenna_(radio)http://en.wikipedia.org/wiki/Radio_receiverhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)http://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Cellular_telephonehttp://en.wikipedia.org/wiki/Cellular_telephonehttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Kilowatthttp://en.wikipedia.org/wiki/Microwatthttp://en.wikipedia.org/wiki/Nanowatthttp://en.wikipedia.org/wiki/Point-to-point_communication_(telecommunications)http://en.wikipedia.org/wiki/Broadcastinghttp://en.wikipedia.org/wiki/Edwin_Armstronghttp://en.wikipedia.org/wiki/Lee_de_Foresthttp://en.wikipedia.org/wiki/John_Logie_Bairdhttp://en.wikipedia.org/wiki/Philo_Farnsworthhttp://en.wikipedia.org/wiki/Telecommunication#cite_note-plunkettresearch.com-0http://en.wikipedia.org/wiki/Communication_systemhttp://en.wikipedia.org/wiki/Transmitterhttp://en.wikipedia.org/wiki/Signal_(electrical_engineering)http://en.wikipedia.org/wiki/Transmission_mediumhttp://en.wikipedia.org/wiki/Free-space_optical_communicationhttp://en.wikipedia.org/wiki/Receiver_(radio)http://en.wikipedia.org/wiki/Radio_stationhttp://en.wikipedia.org/wiki/Electronic_amplifierhttp://en.wikipedia.org/wiki/Antenna_(radio)http://en.wikipedia.org/wiki/Radio_receiverhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)http://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Cellular_telephonehttp://en.wikipedia.org/wiki/Cellular_telephonehttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Kilowatthttp://en.wikipedia.org/wiki/Microwatthttp://en.wikipedia.org/wiki/Nanowatthttp://en.wikipedia.org/wiki/Point-to-point_communication_(telecommunications)http://en.wikipedia.org/wiki/Broadcasting


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Telecommunications in which multiple transmitters and multiple receivers have been designed tocooperate and to share the same physical channel are called multiplex systems.

Analog versus digital communications

Communications signals can be either by analog signals or digital signals. There are analogcommunication systems and digital communication systems. For an analog signal, the signal isvaried continuously with respect to the information. In a digital signal, the information isencoded as a set of discrete values (for example, a set of ones and zeros). During the propagationand reception, the information contained in analog signals will inevitably be degraded byundesirable physical noise. (The output of a transmitter is noise-free for all practical purposes.)Commonly, the noise in a communication system can be expressed as adding or subtracting fromthe desirable signal in a completely random way. This form of noise is called "additive noise",with the understanding that the noise can be negative or positive at different instants of time.Noise that is not additive noise is a much more difficult situation to describe or analyze, andthese other kinds of noise will be omitted here.

On the other hand, unless the additive noise disturbance exceeds a certain threshold, theinformation contained in digital signals will remain intact. Their resistance to noise represents akey advantage of digital signals over analog signals.

TELECOMMUNICATIONS NETWORK

A telecommunications network is a collection ofterminals, links and nodes which connecttogether to enable telecommunicationbetween users of the terminals. Networks may use circuit

switching ormessage switching. Each terminal in the network must have a unique address somessages or connections can be routed to the correct recipients. The collection of addresses inthe network is called the address space.

The links connect the nodes together and are themselves built upon an underlying transmissionnetworkwhich physically pushes the message across the link.

Examples of telecommunications networks are:

computer networks the Internet

the telephone network the global Telex network the aeronautical ACARSnetwork
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COMPUTER NETWORK

A computer network, often simply referred to as a network, is a collection of hardwarecomponents and computers interconnected by communications channels that allow sharing ofresources and information.

Networks may be classified according to a wide variety of characteristics such as the mediumused to transport the data, communications protocol used, scale, topology, and organizationalscope.

The rules and data formats for exchanging information in a computer network are defined bycommunications protocols. Well-known communications protocols are Ethernet, a hardware andLink Layer standard that is ubiquitous in local area networks, and the Internet Protocol Suite,which defines a set of protocols for internetworking, i.e. for data communication betweenmultiple networks, as well as host-to-host data transfer, and application-specific datatransmission formats.

Computer networking is sometimes considered a sub-discipline of electrical engineering,telecommunications, computer science, information technology orcomputer engineering, since itrelies upon the theoretical and practical application of these disciplines.

Properties

Computer networks:

i. Facilitate communicationsUsing a network, people can communicate efficiently and easily via email, instant

messaging, chat rooms, telephone, video telephone calls, and video conferencing.ii. Permit sharing of files, data, and other types of information

In a network environment, authorized users may access data and informationstored on other computers on the network. The capability of providing access todata and information on shared storage devices is an important feature of manynetworks.

iii. Share network and computing resourcesIn a networked environment, each computer on a network may access and useresources provided by devices on the network, such as printing a document on ashared network printer.Distributed computing uses computing resources across anetwork to accomplish tasks.

iv. May be insecureA computer network may be used by computer hackers to deploy computerviruses or computer worms on devices connected to the network, or to preventthese devices from normally accessing the network (denial of service).

v. May interfere with other technologiesPower line communication strongly disturbs certain forms of radiocommunication, e.g., amateur radio. It may also interfere with last mile accesstechnologies such as ADSL andVDSL.
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vi. May be difficult to set upA complex computer network may be difficult to set up. It may also be verycostly to set up an effective computer network in a large organization or company.

Communication media

Computer networks can be classified according to the hardware and associated softwaretechnology that is used to interconnect the individual devices in the network, such as electricalcable, optical fiber, and radio waves (wireless LAN). In the OSI model, these are located atlevels 1 and 2.

A well-knownfamily of communication media is collectively known as Ethernet. It is defined byIEEE 802 and utilizes various standards and media that enable communication between devices.Wireless LAN technology is designed to connect devices without wiring. These devices useradio waves orinfrared signals as a transmission medium.

Wired technologies

Twisted pairwire is the most widely used medium for telecommunication. Twisted-paircabling consist of copper wires that are twisted into pairs. Ordinary telephone wiresconsist of two insulated copper wires twisted into pairs. Computer networking cabling(wired Ethernet as defined by IEEE 802.3) consists of 4 pairs of copper cabling that canbe utilized for both voice and data transmission. The use of two wires twisted togetherhelps to reduce crosstalkand electromagnetic induction. The transmission speed rangesfrom 2 million bits per second to 10 billion bits per second. Twisted pair cabling comesin two forms which are Unshielded Twisted Pair (UTP) and Shielded twisted-pair (STP)which are rated in categories which are manufactured in different increments for various

scenarios.

Coaxial cable is widely used for cable television systems, office buildings, and otherwork-sites for local area networks. The cables consist of copper or aluminum wirewrapped with insulating layer typically of a flexible material with a high dielectricconstant, all of which are surrounded by a conductive layer. The layers of insulation helpminimize interference and distortion. Transmission speed range from 200 million to morethan 500 million bits per second.

ITU-TG.hn technology uses existing home wiring (coaxial cable, phone lines andpowerlines) to create a high-speed (up to 1 Gigabit/s) local area network.

Optical fibercable consists of one or more filaments of glass fiber wrapped in protectivelayers that carries data by means of pulses of light. It transmits light which can travelover extended distances. Fiber-optic cables are not affected by electromagnetic radiation.Transmission speed may reach trillions of bits per second. The transmission speed offiber optics is hundreds of times faster than for coaxial cables and thousands of timesfaster than a twisted-pair wire. This capacity may be further increased by the use ofcolored light, i.e., light of multiple wavelengths. Instead of carrying one message in a
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stream of monochromatic light impulses, this technology can carry multiple signals in asingle fiber.

Wireless technologies

Terrestrialmicrowave Terrestrial microwaves use Earth-based transmitter and receiver.The equipment looks similar to satellite dishes. Terrestrial microwaves use low-gigahertzrange, which limits all communications to line-of-sight. Path between relay stationsspaced approx, 48 km (30 miles) apart. Microwave antennas are usually placed on top ofbuildings, 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. Thesatellites are stationed in space, typically 35,400 km (22,200 miles) (for geosynchronoussatellites) above the equator. These Earth-orbiting systems are capable of receiving andrelaying voice, data, and TV signals.

Cellular and PCS systems Use several radio communications technologies. The systemsare divided to different geographic areas. Each area has a low-power transmitter or radiorelay antenna device to relay calls from one area to the next area.

Wireless LANs Wireless local area network use a high-frequency radio technologysimilar to digital cellular and a low-frequency radio technology. Wireless LANs usespread spectrum technology to enable communication between multiple devices in alimited area. An example of open-standards wireless radio-wave technology is IEEE802.11.

Infrared communication can transmit signals between devices within small distances oftypically no more than 10 meters. In most cases, line-of-sight propagation is used, whichlimits the physical positioning of communicating devices.

A global area network(GAN) is a network used for supporting mobile communicationsacross an arbitrary number of wireless LANs, satellite coverage areas, etc. The keychallenge in mobile communications is handing off the user communications from onelocal coverage area to the next. In IEEE Project 802, this involves a succession ofterrestrial wireless LANs.

Communications protocol

A communications protocol defines the formats and rules for exchanging information via anetwork and typically comprises a completeprotocol suite which describes the protocols used atvarious usage levels. An interesting feature of communications protocols is that they may be and in fact very often are stacked above each other, which means that one is used to carry theother. The example for this is HTTP running overTCP over IP over IEEE 802.11, where thesecond and third are members of the Internet Protocol Suite, while the last is a member of the
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Ethernet protocol suite. This is the stacking which exists between the wireless router and thehome user's personal computer when surfing the World Wide Web.

Communication protocols have themselves various properties, such as whether they areconnection-oriented versus connectionless, whether they use circuit mode orpacket switching, or

whether they use hierarchical or flat addressing.

REFERENCE MODELS

To reduce their design complexity, most networks are organized as a stack of layers or levels,

each one built upon one below it. The number of layers, the name of each layer, the contents of

each layer and the function of each layer differ from network to network. The purpose of each

layer is to offer certain services to the higher layers shielding those layers from the details of

how the offered services are actually implemented. A set of layers and protocols is called

network architecture. A list of protocols used by a certain system, one protocol per layer, is

called a protocol stack. Below we discuss an important network architecture, the OSI reference

model .

THE OSI REFERENCE MODEL

The International Standards Organization (ISO) has developed a reference model for network

design called the Open Systems Interconnection (OSI). It proposes a seven-layer architecture for

networks, as summarized by Figure 1.3.

Figure 1.3

Each layer is characterized by a set of standard protocols which specify its behavior. These seven

layers represent the protocol architecture for the communications component of a host. The

nodes in a network implement only the lower three layers,
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as illustrated in Figure 1.4.

Figure 1.4

The reason for this is that the upper four layers are irrelevant to the task of communication

between the nodes.

In Figure 1.4, when host A sends a message to host B, the message moves down the successive

layers of host A, from the application layer to the presentation layer, to the session layer, etc.,

until it reaches the physical layer. It is then transmitted across the communication line between

host A and node X, and moves up the three layers of node X and down again. Then it is

transmitted to node Y where it goes through the same procedure, and finally is transmitted to

host B, where it moves up its seven layers, until it arrives at the application layer of host B.

Although actual communication takes place only at the physical layer, it is often useful to thinkof virtual communication between corresponding layers. For example, we can use an imaginary

line of communication between the presentation layer on host A and the same layer on host B.

This would be characterized by thepresentation protocol. The termsprotocoland layerare often

used interchangeably. This is harmless but not entirely accurate. Strictly speaking, protocol

refers to the rules and conventions that the functions of a layer should conform to. Layer refers to

a set of services and functions and their realization in hardware or software. A layer is therefore

characterized by its protocol. A set of network layers is also commonly referred to as a protocol

stack.

Each of the seven layers of the OSI model hides the implementation details of the lower layersfrom the upper layers. Well-defined protocols and interfaces for each of the layers make it

possible for the layer to be designed and implemented in isolation from the other layers. Except

for the physical layer, which is implemented in hardware, all other layers are implemented in

software.1 For example, each of these layers may be implemented as a set of routines which

communicate with the layer above and the layer below it via parameters passed in function calls.


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Alternatively, each layer may be implemented as a task (in a multi-tasking environment) which

communicates with other tasks by message passing. Figure 1.5 illustrates the latter.

For house-keeping purposes, each layer adds an additional piece of information to the message it

is transmitting. The same layer removes the additional piece of information on the receiving end.

The additional information appears in form of a header (e.g., TH = Transport Header). The datalink layer adds a header as well as a trailer to its data. Each of the seven layers of the OSI model

is described below in more detail. Subsequent chapters examine the layers in greater depth and

discuss their main protocols. It should be pointed out that the OSI model is not the only model in

use. It is, however, the most-widely respected model and has become a standard benchmark for

comparing other network architectures against.

Figure 1.5 OSI layers as software tasks.

The Physical Layer

The physical layer is concerned with the transmission of raw data bits over communication lines.

Physical layer standards and protocols are concerned with issues such as the following:

i. How a physical circuit is established between communicating devices.

ii. How the circuit is terminated when no longer needed.

iii. The physical form (e.g., voltages, frequencies, timing) in which data bits (binary values 0

and 1) are represented.


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iv. Whether transmission of data can take place in one or both directions over the same

physical connection.

v. Characteristics of the physical media that carry the signals (e.g., copper wire, optical

fiber, radio waves).

vi. Characteristics of the connectors used for connecting the physical media.

vii. How data from a number of sources should be multiplexed before transmission and

demultiplexed upon arrival, and the type of multiplexing technique to be used.

viii. The type of modulation to be used for transmitting digital data over analog transmission

lines.

The physical layer accounts for much of the tangible components of a network, including cables,

satellites, earth stations, repeaters, multiplexers, concentrators, and modems. Physical layer

protocols and standards are of mechanical, electrical, functional, and procedural nature. Thephysical layer hides the above details from the higher layers. To the data link layer, it appears as

a logical communication channel which can send a stream of bits from one point in the network

to another (but not necessarily reliably).

The Data Link Layer

The data link layer is concerned with the reliable transfer of data over the communication

channel provided by the physical layer. To do this, the data link layer breaks the data into data

frames, transmits the frames sequentially over the channel, and checks for transmission errors by

requiring the receiving end to send back acknowledgment frames. Data link protocols are

concerned with the following issues:

i. How to divide the data into frames.

ii. How to delimit frames by adding special bit patterns to the beginning and end of each

frame. This allows the receiving end to detect where each frame begins and where it

ends.

iii. Error detection. Some form of error check is included in the frame header. This is

constructed by the transmitting end based on the contents of the frame, and checked for

integrity by the receiving end. A change in the frame bits can be detected in this way.

iv. Error correction. When a frame arrives corrupted or is for any reason lost in the network,

it is retransmitted. Lost acknowledgment frames may result in duplicate frames, which

need to be detected and corrected as well.


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v. Flow control. In general, not all communication devices in a network operate at the same

speed. Flow control provides a means of avoiding a slow receiver from being swamped

by data from a fast transmitter.

The data link layer hides the above details from the higher layers. To the network layer, it

appears as a reliable communication channel which can send and receive data packets as frames.

The Network Layer

The network layer is concerned with the routing of data across the network from one end to

another. To do this, the network layer converts the data into packets and ensures that the packets

are delivered to their final destination, where they can be converted back into the original data.

Network layer protocols are concerned with the following issues:

i. The interface between a host and the network.

ii. The interface between two hosts across the network.

iii. Routing of packets across the network, including the allocation of a route and handling of

congestion.

iv. Correct ordering of packets to reflect the original order of data.

v. Collection of statistical information (e.g., number of transmitted packets) for performance

measurement and accounting purposes.

vi. Internetworking: communication between two or more networks.

The network layer hides the above details from the higher layers. To the transport layer, it

appears as a uniform data transfer service, regardless of the location of the communicating

devices and how they are connected.

The Transport Layer

The aim of the transport layer is to isolate the upper three layers from the network, so that any

changes to the network equipment technology will be confined to the lower three layers (i.e., at

the node level). Transport layer protocols are concerned with the following issues:

i. Establishment and termination of host-to-host connections.

ii. Efficient and cost-effective delivery of data across the network from one host to another.


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iii. Multiplexing of data, if necessary, to improve use of network bandwidth, and

demultiplexing at the other end.

iv. Splitting of data across multiple network connections, if necessary, to improve

throughput, and recombining at the other end.

v. Flow control between hosts.

vi. Addressing of messages to their corresponding connections. The address information

appears as a part of the message header.

vii. Type of service to be provided to the session layer (e.g., error-free versus error prone

connections, whether messages should be delivered in the order received or not).

The transport layer hides the above details from the higher layers. To the session layer, it appears

as a customized data transfer service between two hosts, isolating the underlying network

technology from it.

The Session Layer

The session layer provides a structured means for data exchange between user processes on

communicating hosts. Session layer protocols are concerned with the following issues:

i. Negotiating the establishment of a connection (a session) between user

ii. processes on communicating hosts, and its subsequent termination. This includes the

setting of various communication parameters for the session (e.g., synchronization and

control).

iii. Correct ordering of messages when this function is not performed by the transport layer.

Recovery from interrupted transport connections, if necessary.

iv. Grouping of messages into a larger message, if necessary, so that the larger message

becomes available at the destination only when its constituent messages have all been

delivered successfully.

The session layer hides the above details from the higher layers. To the presentation layer, itappears as an organized communication service between user processes.

The Presentation Layer

The presentation layer provides a mutually-agreeable binary representation of the application

data communicated between two user processes. Since there are many ways of encoding


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application data (e.g., integers, text) into binary data, agreement on a common representation is

necessary. Presentation layer protocols are concerned with issues such as the following:

i. Abstract representation of application data.

ii. Binary representation of application data.

iii. Conversion between the binary representation of application data and a common format

for transmission between peer applications.

iv. Data compression to better utilize network bandwidth.

v. Data encryption as a security measure.

The presentation layer hides the above details from the higher layers. To the application layer, it

appears as a universal communication service between user processes, regardless of their system-

specific idiosyncrasies, allowing them to converse in a common syntax.

The application layer

The application layer is concerned with the semantics of data, i.e., what the data means to

applications. The application layer provides standards for supporting a variety of application-

independent services. Examples include:

i. Virtual terminal standards to allow applications to communicate with different types of

terminals in a device-independent manner.

ii. Message handling system standards used for electronic mail.

iii. File transfer, access, and management standards for exchanging files or parts thereof

between different systems.

iv. Transaction processing standards to allow different companies with different systems to

access each others on-line databases (e.g., in banking and airline reservation).

v. On-line directory standards for storing details of individuals, organizations, and network

components.

vi. Standards for exchanging formatted documents.

Application layer standards have paved the way for open software systems, in which data can be

communicated between incompatible base systems (i.e., different hardware and software

architectures) without loss of meaning or usefulness.

There exist a multitude of communication protocols, a few of which are described below.


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Ethernet

Ethernet is a family of computer networking technologies for local area networks (LANs)commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replacedcompeting wired LAN technologies.

Systems communicating over Ethernet divide a stream of data into individual packets calledframes. Each frame contains source and destination addresses and error-checking data so thatdamaged data can be detected and re-transmitted.

The standards define several wiring and signaling variants. The original 10BASE5 Ethernet usedcoaxial cable as a shared medium. Later the coaxial cables were replaced by twisted pair andfiber optic links in conjunction with hubs or switches. Data rates were periodically increasedfrom the original 10 megabits per second, to 100 gigabits per second.

Since its commercial release, Ethernet has retained a good degree of compatibility.

Internet Protocol Suite

The Internet Protocol Suite is the set of communications protocols used for the Internet andother similar networks. It is commonly also known as TCP/IP named from two of the mostimportant protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP),which were the first two networking protocols defined in this standard. Modern IP networkingrepresents a synthesis of several developments that began to evolve in the 1960s and 1970s,namely the Internet and local area networks, which emerged during the 1980s, together with the

advent of the World Wide Web in the early 1990s.

The Internet Protocol Suite consists of four abstraction layers. From the lowest to the highestlayer, these are the Link Layer, the Internet Layer, the Transport Layer, and the ApplicationLayer. The layers define the operational scope or reach of the protocols in each layer, reflectedloosely in the layer names. Each layer has functionality that solves a set of problems relevant inits scope.

The Link Layercontains communication technologies for the local network the host is connectedto directly, the link. It provides the basic connectivity functions interacting with the networkinghardware of the computer and the associated management of interface-to-interface messaging.

The Internet Layerprovides communication methods between multiple links of a computer andfacilitates the interconnection of networks. As such, this layer establishes the Internet. It containsprimarily the Internet Protocol, which defines the fundamental addressing namespaces, InternetProtocol Version 4 (IPv4) and Internet Protocol Version 6 (IPv6) used to identify and locatehosts on the network. Direct host-to-host communication tasks are handled in the TransportLayer, which provides a general framework to transmit data between hosts using protocols likethe Transmission Control Protocol and the User Datagram Protocol (UDP). Finally, the highest-level Application Layer contains all protocols that are defined each specifically for the
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functioning of the vast array of data communications services. This layer handles application-based interaction on a process-to-process level between communicating Internet hosts.

SONET/SDH

Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) arestandardized multiplexing protocols that transfer multiple digital bit streams overoptical fiberusing lasers or light-emitting diodes (LEDs). Lower data rates can also be transferred via anelectrical interface. The method was developed to replace the Plesiochronous Digital Hierarchy(PDH) system for transporting larger amounts of telephone calls and data traffic over the samefiber without synchronization problems.

SONET and SDH, which are essentially the same, were originally designed to transport circuitmode communications from a variety of different sources, but they were primarily designed to

support real-time, uncompressed, circuit-switched voice encoded in PCM format. The primarydifficulty in doing this prior to SONET/SDH was that the synchronization sources of thesevarious circuits were different. This meant that each circuit was actually operating at a slightlydifferent rate and with different phase. SONET/SDH allowed for the simultaneous transport ofmany different circuits of differing origin within a single framing protocol. SONET/SDH is notitself a communications protocolper se, but a transport protocol.

Due to SONET/SDH's essential protocol neutrality and transport-oriented features, SONET/SDHwas the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames. It quicklyevolved mapping structures and concatenated payload containers to transport ATM connections.In other words, for ATM (and eventually other protocols such as Ethernet), the internal complex

structure previously used to transport circuit-oriented connections was removed and replacedwith a large and concatenated frame into which ATM cells, IP packets, or Ethernet frames areplaced.

Asynchronous Transfer Mode

Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication

networks. It uses asynchronous time-division multiplexing,[1][2] and it encodes data into small,

fixed-sized cells. This differs from networks such as the Internet or Ethernet LANs that use

variable sizedpackets orframes. ATM provides data link layerservices that run overOSILayer

1 physical links. ATM has functional similarity with both circuit switched networking and small

packet switched networking. This makes it a good choice for a network that must handle bothtraditional high-throughput data traffic (e.g., file transfers), and real-time, low-latency content

such as voice and video. ATM uses a connection-oriented model in which a virtual circuit must

be established between two endpoints before the actual data exchange begins.[2]ATM is a core

protocol used over the SONET/SDH backbone of the public switched telephone network(PSTN)

and Integrated Services Digital Network(ISDN), but its use is declining in favor ofAll IP.
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Scale

Networks are often classified by their physical or organizational extent or their purpose. Usage,trust level, and access rights differ between these types of networks.

Personal area network

Apersonal area network(PAN) is a computer network used for communication among computerand different information technological devices close to one person. Some examples of devicesthat are used in a PAN are personal computers, printers, fax machines, telephones, PDAs,scanners, and even video game consoles. A PAN may include wired and wireless devices. Thereach of a PAN typically extends to 10 meters. [11] A wired PAN is usually constructed with USBand Firewire connections while technologies such as Bluetooth and infrared communicationtypically form a wireless PAN.

Local area network

A local area network (LAN) is a network that connects computers and devices in a limitedgeographical area such as home, school, computer laboratory, office building, or closelypositioned group of buildings. Each computer or device on the network is a node. Current wiredLANs are most likely to be based on Ethernet technology, although new standards like ITU-TG.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phonelines and power lines).

All interconnected devices must understand the network layer (layer 3), because they arehandling multiple subnets. The defining characteristics of LANs, in contrast to WANs (WideArea Networks), include their higher data transfer rates, smaller geographic range, and no need

for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologiesoperate at speeds up to 10 Gbit/s. This is the data transfer rate. LANs can be connected to Widearea network by using routers.

Home network

A home networkis a residential LAN which is used for communication between digital devicestypically 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 orDigital Subscriber Line (DSL) provider.

Campus network

A campus network is a computer network made up of an interconnection of LANs within alimited geographical area. The networking equipment (switches, routers) and transmission media
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(optical fiber, copper plant, Cat5 cabling etc.) are almost entirely owned (by the campus tenant /owner: an enterprise, university, government etc.).

In the case of a university campus-based campus network, the network is likely to link a varietyof campus buildings including, for example, academic colleges or departments, the university

library, and student residence halls.

Backbone network

A backbone network is part of a computer network infrastructure that interconnects variouspieces of network, providing a path for the exchange of information between different LANs orsubnetworks. A backbone can tie together diverse networks in the same building, in differentbuildings in a campus environment, or over wide areas. Normally, the backbone's capacity isgreater than that of the networks connected to it.

A large corporation which has many locations may have a backbone network that ties all of these

locations together, for example, if a server cluster needs to be accessed by different departmentsof a company which are located at different geographical locations. The equipment which tiesthese departments together constitute the network backbone. Network performance managementincluding network congestion are critical parameters taken into account when designing anetwork backbone.

A specific case of a backbone network is the Internet backbone, which is the set of wide-areanetwork connections and core routers that interconnect all networks connected to the Internet.

Metropolitan area network

A Metropolitan area network(MAN) is a large computer network that usually spans a city or a

large campus

Wide area network

A wide area network(WAN) is a computer network that covers a large geographic area such as acity, country, or spans even intercontinental distances, using a communications channel thatcombines many types of media such as telephone lines, cables, and air waves. A WAN oftenuses transmission facilities provided by common carriers, such as telephone companies. WANtechnologies generally function at the lower three layers of the OSI reference model: thephysicallayer, the data link layer, and the network layer.

Enterprise private network

An enterprise private network is a network built by an enterprise to interconnect variouscompany sites, e.g., production sites, head offices, remote offices, shops, in order to sharecomputer resources.
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Virtual private network

A virtual private network (VPN) is a computer network in which some of the links betweennodes are carried by open connections or virtual circuits in some larger network (e.g., theInternet) 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 issecure communications through the public Internet, but a VPN need not have explicit securityfeatures, such as authentication or content encryption. VPNs, for example, can be used toseparate the traffic of different user communities over an underlying network with strongsecurity features.

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 topologymore complex than point-to-point.

Internetwork

An internetwork is the connection of multiple computer networks via a common routingtechnology using routers. The Internet is an aggregation of many connected internetworksspanning the Earth.

Organizational scope

Networks are typically managed by organizations which own them. According to the owner'spoint of view, networks are seen as intranets or extranets. A special case of network is theInternet, which has no single owner but a distinct status when seen by an organizational entity that of permitting virtually unlimited global connectivity for a great multitude of purposes.

Intranets and extranets

Intranets and extranets are parts or extensions of a computer network, usually a LAN.

An intranet is a set of networks, using the Internet Protocol and IP-based tools such as webbrowsers 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. Mostcommonly, an intranet is the internal network of an organization. A large intranet will typicallyhave at least one web server to provide users with organizational information.

An extranet is a network that is limited in scope to a single organization or entity and also haslimited connections to the networks of one or more other usually, but not necessarily, trustedorganizations or entitiesa company's customers may be given access to some part of itsintranetwhile at the same time the customers may not be considered trusted from a securitystandpoint. Technically, an extranet may also be categorized as a CAN, MAN, WAN, or othertype of network, although an extranet cannot consist of a single LAN; it must have at least oneconnection with an external network.
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Internet

The Internet is a global system of interconnected governmental, academic, corporate, public, andprivate computer networks. It is based on the networking technologies of the Internet ProtocolSuite. It is the successor of the Advanced Research Projects Agency Network (ARPANET)

developed by DARPA of the United States Department of Defense. The Internet is also thecommunications backbone underlying the World Wide Web (WWW).

Participants in the Internet use a diverse array of methods of several hundred documented, andoften standardized, protocols compatible with the Internet Protocol Suite and an addressingsystem (IP addresses) administered by the Internet Assigned Numbers Authority and addressregistries. Service providers and large enterprises exchange information about the reachability oftheir address spaces through the Border Gateway Protocol (BGP), forming a redundantworldwide mesh of transmission paths.

Network topology

Common layouts

A network topology is the layout of the interconnections of the nodes of a computer network.Common layouts are:

i. Bus network

A bus network topology is a network architecture in which a set ofclients are connected via ashared communications line, called a bus.. This was the layout used in the original Ethernet,called 10BASE5 and 10BASE2.

How it works

Bus networks are the simplest way to connect multiple clients, but may have problems when twoclients want to transmit at the same time on the same bus. Thus systems which use bus networkarchitectures normally have some scheme of collision handling or collision avoidance forcommunication on the bus, quite often using Carrier Sense Multiple Access or the presence of abus masterwhich controls access to the shared bus resource.
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A true bus network ispassive the computers on the bus simply listen for a signal; they are notresponsible for moving the signal along. However, many active architectures can also bedescribed as a "bus", as they provide the same logical functions as a passive bus; for example,switched Ethernet can still be regarded as a logical network, if not a physical one.

With the dominance of switched Ethernet over passive Ethernet, passive bus networks areuncommon in wired networks. However, almost all current wireless networks can be viewed asexamples of passive bus networks, with radio propagation serving as the shared passive medium.

The bus topology makes the addition of new devices straightforward. The term used to describeclients is station or workstation in this type of network. Bus network topology uses a broadcastchannel which means that all attached stations can hear every transmission and all stations haveequal priority in using the network to transmit[1] data.

The Ethernet bus topology works like a big telephoneparty line before any device can send a

packet, devices on the bus must first determine that no other device is sending a packet on thecable. When a device sends its packet out over the bus, every other network card on the bus seesand reads the packet. Ethernets scheme of having devices communicate like they were in chatroom is called Carrier Sense Multiple Access/ Collision Detection (CSMA/CD). Sometimes twocards talk (send packets) at the same time. This creates a collision, and the cards themselvesarbitrate to decide which one will resend its packet first. All PCs on a bus network share acommon wire, which also means they share the data transfer capacity of that wire or, in techterms, they share its bandwidth.

This creates an interesting effect. Ten PCs chatting on a bus each get to use a much higherproportion of its total bandwidth than, for instance, 100 PCs on the same bus (in this case, one

tenth compared to one hundredth). The more PCs on a bus, the more likely youll have acommunication traffic jam.

Advantages and disadvantages of a bus network

Advantages

Easy to implement and extend.
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Easy to install. Well-suited for temporary or small networks not requiring high speeds (quick setup),

resulting in faster networks. less expensive than other topologies (But in recent years has become less important due

to devices like a switch)

Cost effective; only a single cable is used. Easy identification of cable faults.

Disadvantages

Limited cable length and number of stations. If there is a problem with the cable, the entire network breaks down. Maintenance costs may be higher in the long run. Performance degrades as additional computers are added or on heavy traffic (shared

bandwidth). Proper termination is required (loop must be in closed path).

Significant Capacitive Load (each bus transaction must be able to stretch to most distantlink).

It works best with limited number of nodes. Commonly has a slower data transfer rate than other topologies. Only one packet can remain on the bus during one clock pulse

ii. Star network

Star networks are one of the most common computer networktopologies. In its simplest form, astar network consists of one central switch, hub or computer, which acts as a conduit to transmitmessages. This consists of a central node, to which all other nodes are connected; this centralnode provides a common connection point for all nodes through a hub. Thus, the hub and leafnodes, and the transmission lines between them, form a graph with the topology of a star. If thecentral node is passive, the originating node must be able to tolerate the reception of an echo ofits own transmission, delayed by the two-way transmission time (i.e. to and from the centralnode) plus any delay generated in the central node. An active star network has an active centralnode that usually has the means to prevent echo-related problems.

The star topology reduces the chance of network failure by connecting all of the systemsto a central node. When applied to a bus-based network, this central hub rebroadcasts alltransmissions received from any peripheral node to all peripheral nodes on the network,sometimes including the originating node. All peripheral nodes may thus communicatewith all others by transmitting to, and receiving from, the central node only. The failureof a transmission line linking any peripheral node to the central node will result in theisolation of that peripheral node from all others, but the rest of the systems will beunaffected.
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It is also designed with each node (file servers, workstations, and peripherals) connecteddirectly to a central network hub, switch, orconcentrator.

Data on a star network passes through the hub, switch, or concentrator before continuingto its destination. The hub, switch, or concentrator manages and controls all functions ofthe network. It is also acts as a repeater for the data flow. This configuration is common

with twisted pair cable. However, it can also be used with coaxial cable oroptical fibrecable.

This is the typical layout found in in a Wireless LAN, where each wireless clientconnects to the central Wireless access point.

Advantages

Better performance: star topology prevents the passing of data packets through anexcessive number of nodes. At most, 3 devices and 2 links are involved in anycommunication between any two devices. Although this topology places a huge overheadon the central hub, with adequate capacity, the hub can handle very high utilization byone device without affecting others.

Isolation of devices: Each device is inherently isolated by the link that connects it to thehub. This makes the isolation of individual devices straightforward and amounts todisconnecting each device from the others. This isolation also prevents any non-centralized failure from affecting the network.

Benefits from centralization: As the central hub is the bottleneck, increasing itscapacity, or connecting additional devices to it, increases the size of the network veryeasily. Centralization also allows the inspection of traffic through the network. Thisfacilitates analysis of the traffic and detection of suspicious behaviour.

Easy to detect faults and to remove parts.

No disruptions to the network when connecting or removing devices.
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Disadvantages

High dependence of the system on the functioning of the central hub Failure of the central hub renders the network inoperable

i. Ring network

: A ring networkis a network topology in which each node connects to exactly two other nodes,forming a single continuous pathway for signals through each node - a ring. Data travels fromnode to node, with each node along the way handling every packet.

Because a ring topology provides only one pathway between any two nodes, ring networks maybe disrupted by the failure of a single link. A node failure or cable break might isolate everynode attached to the ring.

FDDI networks overcome this vulnerability by sending data on a clockwise and acounterclockwise ring: in the event of a break data is wrapped back onto the complementary ringbefore it reaches the end of the cable, maintaining a path to every node along the resulting "C-Ring".

Many ring networks add a "counter-rotating ring" to form a redundant topology. Such "dual ring"networks include Spatial Reuse Protocol, Fiber Distributed Data Interface (FDDI), and ResilientPacket Ring.

802.5 networks -- also known as IBM Token Ring networksavoid the weakness of a ring

topology altogether: they actually use a star topology at the physical layer and a MultistationAccess Unit (MAU) to imitate a ring at the datalinklayer.
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Advantages

Very orderly network where every device has access to the token and the opportunity totransmit

Performs better than a bus topology under heavy network load

Does not require a central node to manage the connectivity between the computers

Disadvantages

One malfunctioning workstation can create problems for the entire network Moves, adds and changes of devices can affect the network Communication delay is directly proportional to number of nodes in the network Bandwidth is shared on all links between devices

ii. Mesh network

Mesh networking (topology) is a type of networking where each node must not only captureand disseminate its own data, but also serve as a relay for other nodes, that is, it must collaborateto propagate the data in the network.

A mesh network can be designed using afloodingtechnique or a routingtechnique. When usinga routing technique, the message propagates along a path, by hoppingfrom node to node until thedestination is reached. To ensure all its paths' availability, a routing network must allow for

continuous connections and reconfiguration around broken or blocked paths, usingself-healingalgorithms. A mesh network whose nodes are all connected to each other is a fully connectednetwork. Mesh networks can be seen as one type of ad hoc network. Mobile ad hoc networks(MANET) and mesh networks are therefore closely related, but MANET also have to deal withthe problems introduced by the mobility of the nodes.

The self-healing capability enables a routing based network to operate when one node breaksdown or a connection goes bad. As a result, the network is typically quite reliable, as there isoften more than one path between a source and a destination in the network. Although mostlyused in wireless scenarios, this concept is also applicable to wired networks and softwareinteraction.

Wireless mesh networks

Wireless mesh networks were originally developed for military applications and are typical ofmesh architectures. Over the past decade the size, cost, and power requirements of radios hasdeclined, enabling more radios to be included within each device acting as a mesh node. Theadditional radios within each node enable it to support multiple functions such as client access,backhaul service, and scanning (required for high speed handover in mobile applications).
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Additionally, the reduction in radio size, cost, and power has enabled the mesh nodes to becomemore modularone node or device now can contain multiple radio cards or modules, allowingthe nodes to be customized to handle a unique set of functions and frequency bands.

A fully connected network: each node is connected to every other node in the network.

Note that the physical layout of the nodes in a network may not necessarily reflect the networktopology. As an example, with FDDI, the network topology is a ring (actually two counter-rotating rings), but the physical topology is a star, because all neighboring connections are routedvia a central physical location.

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Basic hardware components

Apart from the physical communications media themselves as described above, networkscomprise additional basic hardware building blocks interconnecting their terminals, such asnetwork interface cards (NICs), hubs, bridges, switches, and routers.

Network interface cards

A network card, network adapter, or NIC (network interface card) is a piece of computerhardware designed to allow computers to physically access a networking medium. It provides alow-level addressing system through the use ofMAC addresses.

Each Ethernet network interface has a unique MAC address which is usually stored in a smallmemory device on the card, allowing any device to connect to the network without creating anaddress conflict. Ethernet MAC addresses are composed of six octets. Uniqueness is maintainedby the IEEE, which manages the Ethernet address space by assigning 3-octet prefixes toequipment manufacturers. The list of prefixes is publicly available. Each manufacturer is thenobliged to both use only their assigned prefix(es) and to uniquely set the 3-octet suffix of everyEthernet interface they produce.

Repeaters and hubs

A repeater is an electronic device that receives a signal, cleans it of unnecessary noise,

regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, sothat the signal can cover longer distances without degradation. In most twisted pair Ethernetconfigurations, repeaters are required for cable that runs longer than 100 meters. A repeater withmultiple ports is known as a hub. Repeaters work on the Physical Layer of the OSI model.Repeaters require a small amount of time to regenerate the signal. This can cause a propagationdelay which can affect network communication when there are several repeaters in a row. Manynetwork architectures limit the number of repeaters that can be used in a row (e.g. Ethernet's 5-4-3 rule).
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Today, repeaters and hubs have been made mostly obsolete by switches (see below).

Bridges

A network bridge connects multiple network segments at the data link l

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