Introduction to

Networking

BY CHANDAN KISHORE

Network• A network is a collection of computers and devices connected

together via communications devices and media.• Networks allow users to share resources, such as hardware,

software, data and information.• networks through a virtual private network.• A network can be relatively small or extensively large.

A local area network (LAN): is a network that connects computers in a limited geographic area.

A wide area network (WAN): is a network that covers a large geographic area.

• The Internet is a worldwide collection of networks linked together.

Network• PAN• CAN• LAN• MAN• WAN

NetworkAdvantages of using a network • Facilitates communications because people can communicate efficiently

and easily via e-mail, instant messaging, chat rooms, telephony, and

videoconferencing.

• Reduce cost by sharing hardware (i.e., a printer) and software

(e.g., using a network version or site license of a program).

• Sharing data and information stored on other computers on the

network. • Allow tight control over who has access to what data.

Disadvantages of using a network • The hardware, software, and expertise required to set up a network

can be expensive. • Networks are vulnerable to security problems. • If the server fails to work, the complete network may also fail to work.

Types of Network• Based on the computing model used, networks are classified into three

types namely: Client-Server Network, Peer to Peer Network and Hybrid Network.

• Based on the size, distance covered and transmission media used, networks are classified into four types namely: LAN, MAN, WAN and GAN.

LAN (Local Area Network)• Used to interconnect computers and PCs within a relatively small area such

as a building, office or campus.• Covers distance of up to 5 to 10 km. • Speed 10 Mbps to 100 Mbps.

MAN (Metropolitan Area Network)• Covers a Metropolitan city.• It connects many LANs located at different office buildings.• It has larger geographical scope compared to LAN.• Covers distance up to few hundred km.• Speed 1.5 to 150 Mbps.

Types of NetworkWAN (Wide Area Network)• Used to interconnect computers over a very large geographic area such as

different cities within the country. • Covers distance of up to 100 km to 1000 km. • Speed 1.5 Mbps to 2.4 Gbps. GAN (Global Area Network)• Are the network connections between countries around the globe.• A good example is “Internet”.• Its reach is several thousand km.• Speed 1.5 Mbps to 100 Gbps.

Network TopologyThe physical structure by which computers are connected, represents the

physical topology of the network.• Term “topology” refers to the way in which the end points or stations or

computer systems, attached to the network.• Topology Selection parameters: ease of installation, ease of reconfiguration,

ease of trouble shooting and number of nodes affected in case of media failure.

Network TopologyFive basic topologies are as follows.Mesh, Star, Bus, Ring and Tree.Mesh Topology • It has dedicated point – to – point link between

devices.• It requires n(n-1)/2 physical channels to connect

‘n’ devices (every device must have n -1 I/O ports).

Advantages• Dedicated link eliminates the traffic problem.• Failure of one link does not affect the entire

network/system.• Privacy is maintained because of dedicated link.• Point to Point link makes fault identification and

fault isolation easy.Disadvantages• High amount of cabling.• High number of I/O ports.

Mesh

Network TopologyStar Topology • Every computer is connected through a cable

to a centrally located device called as hub or switch.

Advantages• Easy to modify and add new computer.• Less expensive than mesh topology.• Each device needs only one link and one

port.• Easy to install and configure.• Single node failure does not affect the

network.• Easy to diagnose the network faults.Disadvantages• Failure of central hub/switch brings the entire

network down.• More cabling required as compared to ring

and bus topology.

Star

Network TopologyBus Topology • One long cable acts as a back bone. • Nodes are connected to the bus cable by using drop lines and taps.• A drop line running between the device and main cable.• A tap is a connector (T connector) that splices into the main cable.• Terminating points are placed at each end. Advantages• Simple, reliable, easy to use and less cabling.• Easy for installation and cheaper than other topologies.Disadvantages• Used only in relatively small networks and a fault on the back bone cable

stops all transmission.• Adding new node and also Fault identification is difficult.• Increase in number of computers degrades the performance of the network.

Bus

Network TopologyRing Topology • Each device has a dedicated point to

point line configuration only with two devices on either side of it.

• Signals travel in one direction from one node to all other nodes around the loop.

Advantages• Easy to install and reconfigure, adding or

deleting new node is easy.• No signal loss since data is regenerated

at each node.• No terminators required.Disadvantages• A break in ring can stop the transmission

in the network.• Difficult to trouble shoot. • Expensive than other topologies.

Ring

Network TopologyTree Topology • It is similar to star topology, but

the nodes are connected to the secondary hub which in turn connected to the central hub.

• A central hub is an active hub (regenerates the signals).

• Secondary hubs are either active or passive hubs.

• A passive hub provides simple physical connection between attached devices.

Transmission Media• The physical path through which computers can send and receive electronic

signals is called as transmission media.

• Electronic signals can be send by using electric currents, radio waves, microwaves, light spectrum etc.

• Transmission media can be classified into two main types

1. Guided Transmission Media

2. Unguided Transmission Media

• Guided Transmission Media

• It has a central conductor enclosed in a plastic jacket.

• They are typically used for small LANs.

• Uses lower end of electromagnetic spectrum such as simple electricity and some times radio waves (in electronic circuits).

• Examples: Twisted pair, Coaxial cable, Fiber optic cable etc.

• Unguided Transmission Media

• Known as wireless media.

• Uses higher electromagnetic frequencies such as radio waves, microwaves and infrared.

• Necessary for mobile computers.

• Examples: Radio waves, Microwaves and Infrared etc.

Transmission MediaTo choose best type of transmission media for the network following factors are

considered.

1. Cost

2. Installation

3. Bandwidth capacity: capacity of medium is usually measured in bandwidth, (bandwidth is measured in terms of Mega bits per second).

4. Node capacity: it is how many computers you can easily attach to the network cable.

5. Attenuation: electromagnetic signals tends to weaken during transmission, refers to attenuation. This phenomenon imposes limits on the distance a signal can travel through medium without an unacceptable degradation.

6. Electromagnetic interference: it affects the signal that is send through the transmission media. EMI is caused by outside electromagnetic waves such as noise.

Guided Transmission MediaTwisted pair

• It is commonly used as telecommunications cable.

• To decrease the amount of cross talk and outside interference the wire are twisted to each other.

• These are two – color coded, insulated copper wire that are twisted around each other.

• Consist of one or more twisted pairs in a common jacket.

Twisted Pair: UTPUnshielded Twisted pair

• Consist of number of twisted-pairs with simple plastic casing.

• Commonly used in telephone systems and computer systems.

• EIA (Electrical Industries Association) divides UTP into different categories.

UTP: RJ-45 Connector

Twisted Pair: UTPCATEGORY BANDWIDTH

(MHz)

MAXIMUM DATA RATE APPLICATION

CAT1 <1 <100 Kbps Telephone/ISDN

CAT2 4 4 Mbps IBM Token ring LANs / T1-Lines

CAT3 16 16 Mbps

(3-4 twists/ foot)

10 Base-T LANs

Currently used in Telephone Lines

CAT4 20 20 Mbps 16 Mbps Token ring LANs

CAT5 100 100 Mbps

1000 Mbps (using 4 pairs)

(3-4 twists/ inch)

100 Base – T (Fast Ethernet)

155 Mbps ATM / Gigabit Ethernet

CAT5E 100 100 Mbps

1000 Mbps (using 4 pairs)

100 Base – T (Fast Ethernet)

155 Mbps ATM / Gigabit Ethernet

CAT6 200-250 1 Gbps Gigabit Ethernet

CAT7 600 1 Gbps Gigabit Ethernet

(over long distance than CAT6)

Twisted Pair: STPShielded Twisted pair

• Consist of shield (aluminum/polyester) between outer jacket and wires.

• Shield makes STP less susceptible to EMI because it is grounded.

• More reliable for LANs, it was the first TP cable used in LANs .

• Used in IBM’s token ring Networks.

• It offers 16 Mbps data rate.

Coaxial cable• Consist of 2 conductors shares the same axis.

• A solid copper wire runs down the center of the cable, surrounded by Insulator (PVC), surrounded by second conductor (shield), surrounded by insulator and thick plastic jacket forms the cover of the cable.

• Classified by size RG (Radio grade) and cable’s resistance to DC and AC measured in ohms.

• Used in TV cable distribution, Long distance Telephone lines and LANs.

• It offers data rate typically 10 Mbps.

• Also carry over 10,000 voice channels (FDM)

Coaxial cable

Coaxial cableType Application

50 ohm, RG-8 and RG-11 Thick Ethernet

50 ohm, RG-58 Thin Ethernet

75 ohm, RG-59 TV cable

93 ohm, RG-62 ARCnet

BNC (Bayonet Neill-Connector) connectors

Fiber Optic cable• It has inner core of glass/plastic that conducts the light, surrounded by

cladding.

• Fiber is surrounded by plastic sheath which can be tight or loose.

• In tight configuration plastic sheath is surrounded by fibers/wires to strengthen the cable.

• In loose configuration space between plastic sheath and outer jacket is filled with liquid gel.

• It offers data rates from 100 Mbps – 2 Gbps.

• For back bone networks offers data rate of 1600 Gbps.

• Also used in TV cables.

Fiber Optic cable: Propagation modes1) Multimode

– Multiple beams from a light source move through the core.

i) Step-index fiber

• The density of core remains constant from the center to the edge.

• A beam of light moves in a straight line – suddenness of the change.

ii) Graded-index fiber

• Density is highest at the center of the core and decreases gradually to its lowest at the edge.

• Decreases the distortion of the signal.

2) Single-mode

– Single-mode uses step-index fiber and a highly focused source of light that limits beams to a small range of angles.

• Propagation of different beams is almost identical.

• All beams arrive at the destination “together” with little distortion.

Fiber Optic cable: Propagation modes

Fiber Optic cable: Fiber types

Fiber-optic cable connectors• SC (subscriber channel) connector: used in cable TV.• ST (straight-tip) connector: used for connecting cable to networking devices.• MT-RJ: a new connector with the same size as RJ45 (UTP connector).

Unguided Transmission Media• Unguided transmission media transport Unguided transmission media transport electromagnetic waveselectromagnetic waves without without

using a physical conductor. using a physical conductor. • This type of communication is often referred to as wireless This type of communication is often referred to as wireless

communication.communication.

• For example: Radio waves, Micro waves, Infrared etc.

• Electromagnetic spectrum used for wireless communication is 3 KHz – 900 THz.

BandsBandsThe section of the electromagnetic spectrum defined as radio waves and The section of the electromagnetic spectrum defined as radio waves and

microwaves is divided into eight ranges, called as microwaves is divided into eight ranges, called as bandsbands. . • Each range is regulated by government authorities.Each range is regulated by government authorities.

• These bands are rated from very low frequency (VLF) to extremely high frequency (EHF).

Bands (Radio waves and Microwaves)Unguided Transmission Media

Unguided Transmission MediaRadio WavesRadio Waves • Electromagnetic waves ranging in frequencies between 3 kHz and 1 GHz Electromagnetic waves ranging in frequencies between 3 kHz and 1 GHz

are normally called as are normally called as radio wavesradio waves..

• Radio waves: Omni directional – propagated in all directions.

• Can travel for long distances and also penetrate the walls for example: AM radio.

• Applications: AM and FM radio, television, cordless phones and paging are the examples of multicasting (one sender many receivers).

• Omni directional antenna: send out signals in all directions, used for multicast communications such as radio, television and paging systems.

Omni directional antenna

Unguided Transmission MediaMicro WavesMicro Waves • Electromagnetic waves ranging in frequencies between 1 and 300 GHz are Electromagnetic waves ranging in frequencies between 1 and 300 GHz are

normally called as normally called as Micro wavesMicro waves..

• Micro waves: Unidirectional and narrowly focused (sending and receiving antennas need to aligned).

• Micro wave propagation is line-of-sight and repeaters are often needed for long distance communication.

• Very high frequency microwaves cannot penetrate walls (disadvantage).

• Microwave band is relatively wide almost, 299 GHz (due to wider sub-bands high data rate is possible).

• Use of certain bands requires permission from authorities.

• Applications: Microwaves are very useful when Unicast (one to one) communication is needed between sender and receiver. Used in cellular phones, satellite networks and wireless LANs.

Unguided Transmission MediaUnidirectional antennae• Two types of antennas are used for Microwaves: parabolic dish and the horn. • A parabolic dish antenna: it works as a funnel, catching a wide range of waves and

directing them to a common point.• Outgoing transmissions are broadcast through a horn aimed at the dish. The

microwaves hit the dish and are deflected outward in a reversal of the receipt path.• A horn antenna: looks like gigantic scoop.• Outgoing transmissions are broadcast up a stem and deflected outward in a series of

narrow parallel beams by the curved head.• Received transmissions are collected by the scooped shape of the horn and deflected

down into the stem.

Unguided Transmission MediaMicro WavesMicro Waves: : Terrestrial Microwave

• Uses Parabolic dish.

• Uses Focused beam.

• Line of sight is maintained.

• Used in Long haul telecommunications.

• Higher frequencies give higher data rates.

Unguided Transmission MediaMicro WavesMicro Waves: : Satellite Microwave

• Satellite acts as relay station (repeater).

• Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency.

• Requires geo-stationary orbit - Height of 35,784km.• Used in Television, Long distance telephone and Private business networks.

Unguided Transmission MediaInfraredInfrared

• It uses Frequency range from 300 GHz – 400 THz.

• It can be used for short-range communication in a closed area using line-of-sight propagation.

• Due to it’s high frequency range, cannot penetrate the walls.• Cannot be used outside the building: interfered by the sun’s rays.

• Applications: the IrDA (Infrared Data Association) has established standard for using these signals for the communication between devices such as keyboards, mice, PCs and printers (for example some manufacturers uses IrDA port that allows communication between wireless keyboard and PC).

• The standard originally defined a data rate of 75 kbps for a distance of up to 8 meter.

• The recent standard defines data rate of 4 Mbps.

• Also used in remote controls of TV, VCD player, DVD player etc.

Switching• Switching allows temporary connections to be established,

maintained and terminated between sources and destinations. • Long distance transmission is typically done over a network of switched

nodes.

• Nodes not concerned with content of data.

• End devices are stations

– Computer, terminal, phone, etc.

• A collection of nodes and connections is a communications network.

• Data routed by being switched from node to node.

• Traditionally there are three methods of Switching

1) Circuit Switching

2) Packet Switching

3) Message Switching

Circuit Switching • Dedicated communication path (physical connection) is established between

two stations (such as phones or computers).• Three phases

– Establish– Transfer– Disconnect

• Must have switching capacity and channel capacity to establish connection.• Must have intelligence to work out routing. • Inefficient

– Channel capacity dedicated for duration of connection.– If no data, capacity wasted.

• Set up (connection) takes time.• Once connected, transfer is transparent.• Developed for voice traffic (phone).• It uses today either of two technologies. - Space division switches (Space division switched network) - Time division switches (Time division multiplexed network)

Circuit Switching Space division switches (Space division switched network) • The paths in the circuit are separated from each other spatially. • Originally designed for analog networks (but currently used in both analog and digital

networks) • Cross-bar switches: connects ‘n’ inputs to ‘m’ outputs in a grid by using

micro-switches (transistors) at each cross point.• Multi-stage switches: it combines cross-bar switches in several stages. Devices are

linked to switches that in turn are linked to hierarchy of other switches.

Space-division switched networkSpace-division switched network Example: Public Telephone Network

Circuit Switching Space division switches (Space division switched network)

Cross-bar switches Multi-stage switches

Circuit Switching Time division switches (Time division multiplexed network) • Uses time division multiplexing to achieve switching. • TSI (Time – Slot Interchange) - it changes the ordering of slots based on the desired connections. - TSI consist of a RAM with several memory locations (input, output

locations and control unit ).

Switching (TSI)

No switching

Packet Switching Note: Circuit switching is designed for voice communication.

It is less suited to data and other non-voice data.

• In packet switching packets are transmitted in discrete units of potentially variable length blocks called as packets.

• Maximum length of packet is decided by network.

• Each packet contains data and header (priority, source and destination address).

• Transmission node to node, routed according to information in the header.

• Two popular approaches: datagram and virtual circuit packet switching.

Packet Switching Datagram Packet Switching

• Each packet is treated independently from all other packets and are referred as datagram packet.

• Datagram packets belongs to same message may go by different paths to reach at the destination.

• Datagram packets arrive out of order at the destination.

• Transport layer reorders them at the destination.

Packet Switching Virtual Circuit Packet Switching

• Relation between all packets belonging to same message is preserved.

• Route is selected at the beginning of the session.

• Packets of same message travels along the same route one after another.

• Implemented in two ways: Switched Virtual Circuit (SVC) and Permanent virtual circuit (PVC).

Switched Virtual Circuit (SVC):

• Like dial up lines in circuit switching.

• Circuit is created whenever needed and exist only for the duration of specific exchange.

Packet Switching Permanent virtual circuit (PVC)• Like leased lines in circuit switching.

• In this same virtual circuit is provided between two users on a continuous basis.

• Circuit is dedicated to specific users and no one else can use it.

• It can be used without connection establishment and connection termination.

Message Switching • Best known by term store and forward.

• It was common in the 1960s and 1970s.

• A node receives a message, stores it until the appropriate route is free, then it sends along.

• The messages are stored and relayed from secondary storage (disk).

• Requirement of large capacity storage media at each node.

Network Interface Card (NIC)• For any computer, a network interface card (NIC) performs two crucial tasks

– Establishes and manages the computer’s network connection.– Translates digital computer data into signals (appropriate for the networking medium)

for outgoing messages, and translates signals into digital computer data for incoming messages.

• NIC establishes a link between a computer and a network, and then manages that link.• NICs also manage transformations in network data’s form

– The computer bus has series of parallel data lines• Parallel transmission

• For nearly all forms of networking media, signals traversing the media consist of a linear sequence of information that corresponds to a linear sequence of bits of data (serial transmission).

• To redistribute serial data to parallel lines (and vice versa), one of the most important components on a NIC is memory, which acts as a buffer.

• Data received in buffer, divided into number of chunks and each chunk consist of SA, DA, data part and CRC field now chunk is referred as data frame.

• Then each Data frame is transmitted serially on the physical line. • Each computer, whether it is attached to a network or not, has an unique physical address

located on the network card.• MAC addresses (physical or hardware addresses) are 48 bits in length and are expressed

as twelve hexadecimal digits.• The first six hexadecimal digital are the organizational unique identifier (OUI) which identify

the manufacturer. The remaining six digits are assigned by vendor (e.g. serial no.)• MAC addresses are known as burned-in-addresses - burned into ROM of NIC and copied

into RAM when the NIC initializes.• It operates at Data Link layer of OSI model.• For example( types of NICs ): Ethernet, Token Ring, FDDI.

Network Interface Card (NIC) and MAC address

NIC Transmission: From Parallel to Serial and Vice Versa

Networking devices: Repeater• Receives the signal before it becomes to weak or corrupted, regenerates the original bit

pattern and puts the refreshed copy back onto the link.• Allows the extension of the physical length of a network.• Doesn’t change the functionality of the network in any way.• Act only upon the electrical components of a signal and are therefore active only at the

physical layer.• The location of the repeater on the link is vital: it must be placed so that a signal reaches it

before any noise changes the meaning of the carried information.• A little noise can alter the precision of a bit voltage without destroying its identity; if the

corrupted bit travels much further, the accumulated noise can change its meaning completely; at that point the original voltage is unrecoverable.

• A repeater placed on the line before this complete loss takes place, will still read the signal well enough to determine the intended voltages and replicate them in their original form.

Networking devices: Hub• They have a number of incoming lines that are joined electrically. Frames coming on one

line (port) are sent on all the other lines (ports).• It forms a single collision domain

– If two frames are arriving at the same time, they will collide in same way as on coaxial cable.

• They don’t examine nor use in any way the 802 addresses.• They operates at the physical layer.• Passive hubs: Frames coming on one line are sent on all the others (passively without

amplifying). • Active hubs: Frames coming on one line are sent on all the others ( by amplifying) and it

functions in a similar manner to a Repeater.

Networking devices: Switch • Similar to bridges in that both route on frame addresses. • The main difference is that switches interconnect individual computers.• It functions at Data Link layer of OSI model.• The switch must actively forward the frame from a station to another (i.e. A to B).• Each port is its own collision domain

– They never loose frames due to collisions.– They may loose frames due to lack of buffer space (when frames came faster than they

can transmit).

Networking devices: Bridge• Connect two or more LANs. • Functions in Data Link layer of OSI model.• Can divide a large network into smaller segments.• Can relay frames between two originally separate

LANs.• Keep the traffic for each segment separated, filtering

the traffic – They are useful to keep the congestion low.

• When frames arrive, software in the bridge extracts the destination address from the frame and looks it up on a table to see where to send it.

– For Ethernet this is 48 bit address (MAC).

LAN-1

LAN-2

LAN-1

LAN-2

Networking devices: Router• Relay packets among multiple interconnected networks.• Functions in Network layer of OSI Model.• Have access to network layer addresses and have two

or more networks at the same time.• A packet sent from a station on one network to a station

on a neighboring network, goes first to the jointly held router, which forwards it to the destination network.

• If the router is not connected to both source and destination network, then the sending router transfers the packet across one of its connected networks to the next router, in the direction of the destination, and so on, until the destination is reached.

Networking devices: Brouter• Functions both as Bridge and a Router – hence called as Brouter.• Can work on networks using different protocols.• Can be programmed only to pass data frames using a specific protocol forward to a segment – in this

case it is functioning in a similar manner to a Bridge.• If a Brouter is set to route data packets to the appropriate network with a routed protocol such as IP,

it is functioning as a Router.

Networking devices: Gateway• Connects 2 or more networks that can be of different types and provides protocol conversion so that

end devices with dissimilar protocol architectures can communicate.• Transport Gateways

– Operate at Transport Layer– Connect two or more computers that use different connection-oriented transport layer protocols.

• i.e. transport gateway translate TCP/IP packet into SPX/IPX packet (Netware).• Application Gateways

– Operate at Application Layer.– Understand the format and contents of the data and translate one format into another

• i.e. an e-mail gateway may translate Internet E-mails into SMS messages of mobile phones.

Gateway

137.22.144.6

145.65.23.102

Netware

TCP/IP

Networking devices- Remote Access Device: Modem1. Allow computers to communicate over a telephone line.2. Enable communication between networks or connecting to the world beyond the LAN.3. Cannot send digital signal directly to telephone line.4. Sending end: MODulate the computer’s digital signal into analog signal and transmits. 5. Receiving end: DEModulate the analog signal back into digital form.6. Modems typically have the following I/O interface:

- A serial RS-232 communication interface. - A RJ-11 telephone-line interface (a telephone plug).

THANK

YOU