Itishree MishraItishree MishraXII AXII A

PC PC

Multiplexer

Media Media

Computer networking devices are Computer networking devices are units that mediate units that mediate data in a  in a computer network. Computer computer network. Computer networking devices are also called networking devices are also called network equipment, Intermediate network equipment, Intermediate Systems (IS)or Interworking Unit Systems (IS)or Interworking Unit (IWU). Units which are the last (IWU). Units which are the last receiver or generate data are receiver or generate data are called called hosts or  or data terminal equipment..

• Separating (connecting)Separating (connecting) networks or networks or expandingexpanding network network• e.g. repeaters, hubs, bridges, e.g. repeaters, hubs, bridges,

routers, switches, gatewaysrouters, switches, gateways

• Remote accessRemote access• e.g. 56K Modems and ADSL e.g. 56K Modems and ADSL

modemsmodems

• Networks cannot be made larger by Networks cannot be made larger by simply adding new computers and simply adding new computers and more cablesmore cables•Less efficient !!Less efficient !!

• Can install components toCan install components to•segment (divide) large LAN to form segment (divide) large LAN to form smaller LANssmaller LANs

•connect LANsconnect LANs• Required componentsRequired components

•Repeaters, bridges, routers, Repeaters, bridges, routers, switches or gatewaysswitches or gateways

ModemModem RJ-45RJ-45 Ethernet cardEthernet card Hub Hub SwitchSwitch RepeaterRepeater BridgeBridge RouterRouter GatewayGateway

A A MODEMMODEM is a is a computer computer peripheral that peripheral that allows you to allows you to connect and connect and communicate communicate eith other eith other computers via computers via telephone lines.telephone lines.

•MODEM stands MODEM stands for for modulation modulation and and demodulation. demodulation.

•Allow Allow computers to computers to communicate communicate over a over a telephone linetelephone line

•Enable Enable communication communication between between networks or networks or connecting to connecting to the world the world beyond the LANbeyond the LAN

• Cannot send digital signal directly to Cannot send digital signal directly to telephone linetelephone line

• Sending end: Sending end: MODMODulate the computer’s ulate the computer’s digital signal into analog signal and digital signal into analog signal and transmits transmits

• Receiving end: Receiving end: DEMDEModulate the analog odulate the analog signal back into digital formsignal back into digital form

2. EXTERNAL 2. EXTERNAL MODEMS:MODEMS:

The modems The modems that are connected that are connected externally to the externally to the computer.computer.

MODEM converts MODEM converts digital signals to A/F digital signals to A/F (Audio Frequency) (Audio Frequency) tones which are in the tones which are in the frequency range that frequency range that the telephone lines the telephone lines can transmit and also can transmit and also it can convert it can convert transmitted tones transmitted tones back to digital back to digital information.information.

RJ 45 is the short for RJ 45 is the short for Registered jack 45Registered jack 45. RJ . RJ 45 is an eight wire 45 is an eight wire connector, which is connector, which is commonly used to commonly used to connect computers on connect computers on the local area networks the local area networks i.e., LAN’s especially i.e., LAN’s especially Ethernets. Ethernets. (Ethernet is a LAN (Ethernet is a LAN architechture architechture developed by Xerox developed by Xerox Corp along with DEC Corp along with DEC and Intel. It uses either and Intel. It uses either bus or star bus or star topologyand suports topologyand suports data transfer rates data transfer rates upto 10 Mbps.) upto 10 Mbps.)

Inserting an RJ-45 connector into Inserting an RJ-45 connector into its jack.its jack.

RJ-45 jack.RJ-45 jack.

Ethernet is a LAN Ethernet is a LAN architecture architecture developed by Xerox developed by Xerox corp. in association corp. in association with DEC and Intel. with DEC and Intel. Ethernet uses either Ethernet uses either bus or star topology bus or star topology and supports data and supports data transfer rates up to 10 transfer rates up to 10 mbps.mbps.

The computers that The computers that are part of Ethernet, are part of Ethernet, have to install a have to install a special card called special card called Ethernet card .Ethernet card .

An Ethernet card contains connections An Ethernet card contains connections for either coaxial or twisted pair cables for either coaxial or twisted pair cables or both.or both.

Inserting Ethernet Inserting Ethernet card in its slot on card in its slot on motherboardmotherboard

HubHub can be defined as one  can be defined as one common point for connectingcommon point for connectingall the network devices. all the network devices. Various Various LAN segments are segments are connected to hub in order to connected to hub in order to organize the working of the organize the working of the network. A network hub connects the network. A network hub connects the

variousvariousports of the optic fiber cable and helpsports of the optic fiber cable and helpsestablish a single network connection orestablish a single network connection orsegment.segment.

The most common operation it performs The most common operation it performs is that it repeats all the information it is that it repeats all the information it

receives and forward it to all receives and forward it to all PC terminals PC terminals attached to it. attached to it. This repetition of data This repetition of data results in unnecessary results in unnecessary data traffic being sent to data traffic being sent to the network. Therefore the data the network. Therefore the data is sent in bulk without the is sent in bulk without the identification of its destination.identification of its destination.

Limitations and Features

•CannotCannot link unlike segments link unlike segments•CannotCannot join segments with different join segments with different access methods (e.g. CSMA/CD and access methods (e.g. CSMA/CD and token passing)token passing)

•Do notDo not isolate and filter packets isolate and filter packets•CanCan connect different types of connect different types of mediamedia

•The most The most economiceconomic way of way of expanding networksexpanding networks

  A network switch is a small hardware A network switch is a small hardware device that joins multiple computers device that joins multiple computers together within one local area network together within one local area network (LAN). Technically, network switches (LAN). Technically, network switches operate at layer two (Data Link Layer) operate at layer two (Data Link Layer) of the OSI model. of the OSI model.

Network switches appear nearly identical Network switches appear nearly identical to network hubs, but a switch generally to network hubs, but a switch generally contains more intelligence (and a slightly contains more intelligence (and a slightly higher price tag) than a hub. higher price tag) than a hub.

Unlike hubs, network switches are capable Unlike hubs, network switches are capable of inspecting data packets as they are of inspecting data packets as they are received, determining the source and received, determining the source and destination device of each packet, and destination device of each packet, and forwarding them appropriately. forwarding them appropriately.

By delivering messages only to the By delivering messages only to the connected device intended, a network connected device intended, a network switch conserves network bandwidth and switch conserves network bandwidth and offers generally better performance than a offers generally better performance than a hub.hub.

A switch is a A switch is a telecommunication device telecommunication device which receives a message which receives a message from any device connected from any device connected to it and then transmits the to it and then transmits the message only to the device message only to the device for which the message was for which the message was meant. This makes the meant. This makes the switch a more intelligent switch a more intelligent device than a hub (which device than a hub (which receives a message and then receives a message and then transmits it to all the other transmits it to all the other devices on its network). The devices on its network). The network switch plays an network switch plays an integral part in most integral part in most modern Ethernet LANs. modern Ethernet LANs. 

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Advantages of Advantages of SwitchesSwitches•Switches divide a network into Switches divide a network into several isolated channels (several isolated channels (or or collision domainscollision domains))•Reduce the possibility of collisionReduce the possibility of collision

• Collision only occurs when two devices try to get Collision only occurs when two devices try to get access to one channelaccess to one channel

• Can be solved by buffering one of them for later Can be solved by buffering one of them for later accessaccess

•Each channel has its own Each channel has its own network capacitynetwork capacity

• Suitable for real-time applications, e.g. video Suitable for real-time applications, e.g. video conferencingconferencing

•Since isolated, hence secureSince isolated, hence secure• Data will only go to the destination, but notData will only go to the destination, but not othersothers

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Limitations of Switches•Although contains buffers to Although contains buffers to accommodate bursts of traffic, accommodate bursts of traffic, can become overwhelmed by can become overwhelmed by heavy trafficheavy traffic•Device cannot detect collision Device cannot detect collision when buffer fullwhen buffer full

• CSMA/CD scheme will not work since the data CSMA/CD scheme will not work since the data channels are isolated, not the case as in channels are isolated, not the case as in EthernetEthernet

•Some higher level protocols do Some higher level protocols do not detect errornot detect error

• E.g. UDPE.g. UDP

•Those data packets are Those data packets are continuously pumped to the continuously pumped to the switch and introduce more switch and introduce more problemsproblems

A repeater is A repeater is an electronic device an electronic device that receives that receives a signal and retransmia signal and retransmits it at a higher level ts it at a higher level or higher power, or or higher power, or onto the other side of onto the other side of an obstruction, so that an obstruction, so that the signal can cover the signal can cover longer distances.longer distances.

In digital communication systems, a repeater is a In digital communication systems, a repeater is a device that receives a digital signal on an device that receives a digital signal on an electromagnetic or optical transmission medium electromagnetic or optical transmission medium and regenerates the signal along the next leg of and regenerates the signal along the next leg of the medium. In electromagnetic media, the medium. In electromagnetic media, repeaters overcome the attenuation caused by repeaters overcome the attenuation caused by free-space electromagnetic-field divergence or free-space electromagnetic-field divergence or cable loss. A series of repeaters make possible cable loss. A series of repeaters make possible the extension of a signal over a distance.the extension of a signal over a distance.

Repeaters remove the unwanted noise in an Repeaters remove the unwanted noise in an incoming signal. Unlike an analog signal, the incoming signal. Unlike an analog signal, the original digital signal, even if weak or distorted, original digital signal, even if weak or distorted, can be clearly perceived and restored. With can be clearly perceived and restored. With analog transmission, signals are restrengthened analog transmission, signals are restrengthened with with amplifiersamplifiers which unfortunately also amplify  which unfortunately also amplify noise as well as information.noise as well as information.

• Has one input and one outputHas one input and one output• Used to Used to isolate network trafficisolate network traffic and and computerscomputers

• Has the intelligent to examine incoming Has the intelligent to examine incoming packet source and destination packet source and destination addresses.addresses.•But But cannotcannot interpret interpret higher-level higher-level informationinformation

•Hence Hence cannotcannot filter packet filter packet according to according to its protocolits protocol

Bridges work at the Bridges work at the Media Access Media Access Control Sub-layerControl Sub-layer of the OSI model. of the OSI model.Routing table is Routing table is built to record built to record the segment no. the segment no. of address.of address.If destination If destination address is in the address is in the same segment same segment as the source as the source address, stop address, stop transmit.transmit.Otherwise, Otherwise, forward to the forward to the other segment.other segment.

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Differences Between Bridges and Differences Between Bridges and RepeatersRepeaters

Repeaters Bridges

OSI layer Physical layer Data link layer

Dataregeneration

Regenerate data atthe signal level

Regenerate dataat the packetlevel

Reduce networktraffic

No Yes

In a common configuration, In a common configuration, routers are used to create larger routers are used to create larger networks by joining two network networks by joining two network segments. segments.

A router can be a dedicated A router can be a dedicated hardware device or a computer hardware device or a computer system with more than one system with more than one network interface and the network interface and the appropriate routing software. All appropriate routing software. All modern network operating modern network operating systems include the functionality systems include the functionality to act as a router.to act as a router.

Routers will normally create, add, Routers will normally create, add, or divide on the Network Layer as or divide on the Network Layer as they are normally IP-based they are normally IP-based devices.devices.

• As packets are passed from As packets are passed from routers to routers, Data Link routers to routers, Data Link layer source and destination layer source and destination addresses are stripped off and addresses are stripped off and then recreatedthen recreated

• Enables a router to route a Enables a router to route a packet from a TCP/IP Ethernet packet from a TCP/IP Ethernet network to a TCP/IP token ring network to a TCP/IP token ring networknetwork

• Only packets with known Only packets with known network addresses will be network addresses will be passed passed - hence reduce traffic- hence reduce traffic

• Routers can listen to a Routers can listen to a network and identify its network and identify its busiest partbusiest part

• Will select the most cost Will select the most cost effective path for transmitting effective path for transmitting packetspackets

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• RoutersRouters are layer 3 are layer 3 devices which devices which recognize network recognize network addressaddress

• BridgesBridges are layer 2 are layer 2 devices which look devices which look at the MAC sublayer at the MAC sublayer node address node address

•BridgesBridges forward forward everything they don’t everything they don’t recognizerecognize

•RoutersRouters select the select the best path best path

Distinguishing Between Bridges and Routers

Any device that translates one data Any device that translates one data format to another is called a format to another is called a gateway.gateway.

A gateway is a network device that A gateway is a network device that connects dissimilar networks. It connects dissimilar networks. It establishes an intelligent establishes an intelligent connection between a local network connection between a local network and external networks with and external networks with completely. different structures.completely. different structures.

•Some examples of gateways include a Some examples of gateways include a router that translates data from one router that translates data from one network protocol to another, a bridge network protocol to another, a bridge that converts between two networking that converts between two networking systems, and a software application that systems, and a software application that converts between two dissimilar converts between two dissimilar formats.formats.

•The key point about a gateway is that The key point about a gateway is that only the data format is translated, not only the data format is translated, not the data itself. In many cases, the the data itself. In many cases, the gateway functionality is incorporated gateway functionality is incorporated into another deviceinto another device.

•The gateway often acts as a proxy The gateway often acts as a proxy server and a firewall.server and a firewall.