Computer Network By Pawan Thakur HOD CS & IT VIM BHOPAL

COMPUTER NETWORK 10-1

10.1. INTRODUCTIONA network consists of two or more computers that are linked together in order to sharethe resources, such as printers, exchange files among computers, with the help of electroniccommunications. The computers on a network may be linked by cables, telephone lines,radio waves, satellites, or infrared light beams etc.

The computer that provides resources to other computers on a network is known asserver. In the network the individual computers, which access shared network resources,are known as workstations or nodes.

A computer network is a network, in which group of computers and devicesinterconnected by communications channels that facilitate communicationsamong users and allow users to share resources.

Network follows the distributed computer processing in which work is processed bymany computers i.e. a single job is not loaded to the single computer which is distributedto several computers.

10.2. GOALS OF COMPUTER NETWORKSThe goals of computer network are as following:

LEARNING OBJECTIVES

At the end of this chapter you will be able to understand :

� Introduction of Network

� Types of Network

� Advantage of Network

� Function of Different OSI Layers

� Inter Networking

� TCP/IP

L

10-2 COMPUTER NETWORK

1. Resource sharing. The first goal of networking is resource sharing. It permits sharingof resources which are available on the network without the regard to the physical locationof the resource and the users.

2. High reliability. The second goal is to provide high reliability. This is achieved byhaving alternative source of resources. For example, all files could be replicated on twoor more machines, so if one of them is unavailable the other copies could be available.

3. Saving money. The third goal is saving money. Small computers have a much betterprice/performance ratio than larger ones. Mainframes are roughly a factor of ten timesfaster than the fastest single chip microprocessors, but they cost thousand times more.This imbalance has caused many system designers to build systems consisting of powerfulpersonal computers, one per user, with data kept on one or more shared file servermachines. This goal leads to networks with many computers located in the same building.Such a network is called a LAN (local area network).

4. Increased the systems performances. The fourth goal of computer networks is toincrease the systems performances as the work load distributed, by just adding morecomputers to the networks.

5. Communication medium. Computer networks provide a powerful communicationmedium. A file that was updated or modified on a network can be seen by the otherusers on the network immediately.

6. Distributed computer processing. The distribute computer processing which onework is processed by many computers i.e. a single job is not loaded to the single computerwhich erase distributed to several computer.

10.3. TYPE OF NETWORKComputer Network can be divided into two different methods :

1. According to Range.

2. According to topology.

10.3.1. According to RangeAccording to range network can be dived into three parts: Local Area Network (LAN),Metropolitan Area Network (MAN), Wide Area Network (WAN).

(a) Local Area Network (LAN). LAN is used in small office building or in a campus.LAN network can be two or more computers are connected with switches as shown inFig. 10.1.


Fig. 10.1. Local Area Network.

In this network those computers and peripherals are connected which shares the datainternally. Mostly, LAN uses same type of transmission media. LAN can be of twotypes: Wired LAN and Wireless LAN.

(b) Metropolitan Area Network (MAN). A metropolitan area network (MAN) is anetwork that connects two or more local area networks or campus area networks togetheras shown in the Fig. 10.2.

Fig. 10.2. Metropolitan Area Network.


It does not extend outside the boundaries of the immediate town/city. Routers, switchesand hubs are connected to create a metropolitan area network.

(c) Wide Area Network (WAN). A wide area network (WAN) is a computer networkthat covers a broad area as shown in the Fig. 10.3.

Fig. 10.3. Wide Area Network.

It is network whose communications links cross metropolitan, regional, or nationalboundaries.

In other words, a WAN is a data communications network that covers a broad geographicarea such as one city to another and one country to another country and that often usestransmission facilities provided by common carriers, such as telephone companies. Theexample of this type of network is internet.

10.3.2. According to TopologyThe term topology in the context of network refers to the way the computers orworkstations in the network are linked together. According to the physical arrangementsof workstations and nature of work, topology network can be dived in to: Bus topologynetwork, Ring topology network, Star topology network and Mesh topology network

(a) Bus topology network. In bus topology all workstations are connected to a singlecommunication line called bus as shown in Fig. 10.4. In this type of network topologythere is no central node as in star topology. Transmission from any station travels thelength of the bus in both directions and can be received by all workstations. The advantageof the bus topology is that

• It is quite easy to set up.

• If one station of the topology fails it does not affect the entire system.

The disadvantage of bus topology is that any break in the bus is difficult to identify.

In the bus topology we use only single cable to connect many computers on nodes in anetwork.


Fig. 10.4. Bus Topology Network.

(b) Ring topology network. This is that network in which computer are connect in theform of close network. A ring topology is a LAN architecture that consists of a series ofdevices or workstation connected to one another by unidirectional transmission links toform a ring as shown in the Fig. 10.5.

Fig. 10.5. Ring Network.

Whenever the message is passed the message contains the information plus address ofthe node, the node before receiving the message checks the message is for the currentnode. This network is very fast and expensive.

The advantage of this topology is that any signal transmitted on the network passesthrough all the nodes. The disadvantage of ring network is that the breakdown of anyone station on the ring can disable the entire system.

(c) Star topology network. In star topology a number of workstations or nodes aredirectly linked to a central node as shown in Fig. 10.6. Any communication betweenstations on a star LAN must pass through the central node. There is bi-directionalcommunication between various workstations. The central node controls all the activitiesof the nodes. The advantages of the star topology are:


• It offers flexibility of adding or deleting of workstations from the network.

• Breakdown of one station does not affect any other devices on the network.

Fig. 10.6. Star Topology.

Signal travels through the hub to all other computers, it requires more cable. If hub goesdown, entire network goes down. If one computer goes down, the network functionsnormally most scalable and reconfigurable topology. The star topology is it uses n(n – 1)wires to connect all the n nodes.

(d) Mesh topology network. The mesh topology connects each computer on thenetwork to the others as shown in Fig. 10.7.

Fig. 10.7. Mesh Topology.


Meshes use a significantly larger amount of network cabling than do the other networktopologies, which makes it more expensive. The mesh topology is highly fault tolerant.Every computer has multiple possible connection paths to the other commuters on thenetwork, so a single cable break will not stop network communications between any twocomputers.

10.3.1. Advantages of NetworksThere are number of advantages of network:

1. Speed. Network provide a very fast method for sharing and transferring files fromone computer to another. Without a network, files are shared by copying them to floppydisks or sending the disks from one computer to another.

2. Security. The network system provides security, which protects the system fromother users. For example : In banking organization the bank can set permission the userto view and manuputate their account with providing thin user identification and password.

3. Cost. Computer network support sharing of a program on a network allows foreasier upgrading of the program. The changes have to be done only once at the fileserver instead of on all the individual workstations.

4. Fast Problem Solving. When we use networks any problem can be sorted outfaster than the single computer because most of the times problems are shared by hedifferent computers.

5. Resource Sharing. Sharing of resources is another area in which a network usefulas compare to stand-alone computers. Most of the organisation cannot afford enoughlaser printers, fax machines, modems, scanners, and CD-ROM players for each computer.However, if these or similar peripherals are added to a network, they can be shared bymany users.

6. Electronic Mail. The presence of a network provides the hardware necessary toinstall an E-Mail system. E-mail aids in personal and professional communication for allorganisation and it facilitates the dissemination of general information to the entireorganisation staff. Electronic mail on a LAN can enable to communicate with others. Ifthe LAN is connected to the Internet, we can communicate with others throughout theworld.

7. Workgroup Computing. Workgroup software (such as Microsoft BackOffice) allowsmany users to work on a document or project concurrently. For example, educatorslocated at various schools within a country could simultaneously contribute their ideasabout new curriculum standards to the same document and spreadsheets.


10.4. ISO- OSI MODELThe international standard organization is a multination body dedicated to worldwide.

An ISO standard that covers all aspects of network communication isthe open system interconnection model. OSI model is not a protocol. It isa model for understanding and designing an international architectureor network architecture.

It divides network architecture into seven layers as shown in Fig. 10.8, from top tobottom, are the Application, Presentation, Session, Transport, Network, Data-Link, andPhysical Layers. It is therefore often referred to as the OSI Seven Layer Model.

Fig. 10.8. ISO-OSI Model.

1. Physical layer. The Physical Layer is the first and lowest layer in the seven-layerOSI model of computer networking. The physical layer functions are to transmit a bitstream over a physical medium. It deals with the specifications of the interface andtransmission medium. It also defines the procedures and functions that physical devicesand interfaces have to perform for transmission to occur.

L


2. Data link layer. The Data Link Layer is Layer 2 of the seven-layer OSI model ofcomputer networking. This layer transforms the physical layer a transmission facility toa reliable link and is responsible for node to node delivery. It makes the physical layerappear error free to the upper layer (network layer).

3. Network layer. The Network Layer is Layer 3 of the seven-layer OSI model ofcomputer networking. This layer is responsible for the source to destination delivery ofa packet possibly across multiple network (links) whereas, the data link layer over seesthe delivery of the packet between the system on the same network (links), the networklayer ensures that each packet gets from its point of origin to its final destination.

4. Transport layer. The Transport layer is Layer 4 of the seven-layer OSI model ofcomputer networking. This layer is responsible for source to destination (end- to end)delivery of the entire message. The transport layer, on the other hand, ensures that thewhole message arrives intact and in order, overseeing both error control and flow controlat the source to destination level. The transport layer may create a connection betweenthe two parts.

5. Session layer. The session layer is Layer 5 of the seven-layer OSI model of computernetworking.This layer is the network dialog controller. It establishers, maintain andsynchronizers the interaction between communicating systems. The main responsibilityof this layer is to control the flow of the communication. It is also concerned that theflow of the communication will be unique reaction by directional. The session layer alsoconsider that the first request is fulfilled or not before receiving the second.

6. Presentation layer. The Presentation Layer is Layer 6 of the seven-layer OSImodel of computer networking. The presentation layer is concerned with the syntax andsemantics of the information exchanged between two systems. Mainly encoding is doneat the presentation layer the presentation layer controls the encoding of the data. Itchanges the one language to another every computer does not uses the data encodingscheme.

7. Application layer. The application layer enable the user, whether human or softwareto access the network. It provides user interfaces and support for services such aselectronic mail remote file access and transfer shared database management, and othertypes of distributed information services.

10.5. FUNCTION OF VARIOUS OSI LAYERSThe functions of various layers in OSI model are given below :

1. Physical layer. The function of physical layer is as following:

(a) Physical interfaces and media. The physical layer defines the features of theinterface between the devices and the transmission medium. It also defines thetype of transmission medium.

(b) Representation of bits. The physical layer data consist of a stream of bitsmust be encoded into signals electrical or optical. The physical layer defines thetype of encoding (how 0s and 1s are changed to signals).


(c) Data rate. The number of bits sent each second is also defined by the physicallayer. In other words the it defines the duration of a bit which is how long it lasts.

(d) Line configuration. The physical layer is concerned with the connection ofdevices to the medium. In a point to point configuration, two devices areconnected together through a dedicated link. In a multipoint configuration a linkis share between several devices.

(e) Physical topology. The physical topology defines how devices are connectedto make a network. Device can be connected using a mesh topology, a startopology, a ring topology or a bus topology.

(f) Transmission mode. The physical layer also defines the direction oftransmission between two device simple, half duplex or full duplex.

2. Data link layer. The responsibilities of the Data link layer are as following:

(a) Framing. The data link layer defines the stream of bits received form the networklayer into data units called frames.

(b) Physical addressing. If frames are to be distributed to different system on thenetwork the data link layer adds the header to the frame to define the physicaladdress of the sender.

3. Network layer. The responsibilities of the network layer include the following:

(a) Logical addressing. The physical addressing implemented by the data linklayer, handles the addressing problems locally. The network layer adds a headerto the packet coming from the upper layer that among other things includes thelogical address of the sender and receiver.

(b) Routing. When networks are connected together to create an internetworkingthat connecting devices (called routers or gateways) route the packets to theirfinal destination. One of the functions of the network layer is to provide thismechanism.

4. Transport layer. The functions of the transport layer include the following:

(a) Service point addressing. Computers often run several programs at the sametime for this reason source to destination delivery means delivery not only fromone computer to the next, but also from a specific process on one computer to aspecific process on the other. The transport layer header therefore, must includea type of address called a service point address.

(b) Segmentation and reassembly. A message is divided into transmittablesegment where each segment containing a sequence number. These numbersenable the transport layer to reassemble the message correctly upon arriving atthe destination and to identify and replace packets that were lost in thetransmission.


(c) Connection control. The transport layer can be either connection less orconnection oriented. A connection oriented transport layer makes a connectionwith the transport layer at the destination machine first before delivering thepackets

(d) Error control. Like the data link layer the transport layer is responsible forerror control.

5. Session layer. The functions of the session layer include are as following:

(a) Dialog control. Dialog control allows the communication between twoprocesses to take place either is half duplex (one way at a time) or full duplex(two way at time).

(b) Synchronization. The session layer allows a process to check synchronizationpoints into a stream of data.

6. Presentation layer. The responsibilities of the presentation layer are as following;

(a) Translation. The process in two systems is usually exchanging information inthe form of character strings, numbers and so on.

(b) Encryption. To carry sensitive information, a system must be able to assureprivacy. Encryption means that the sender transformers the original informationto another form and sends the resulting message over the network. Decryptionreverses, the original process to transform the message back to its original form.

(c) Compression. Data compression reduces the number of bits to be transmitted.

7. Application layer. The functions provided by the application layer are the following:

1. Virtual terminal. A network virtual terminal is a software version of a physicalterminal. It allows a user to log on to a remote host.

2. File transfer access and management (FTAM). This application allows auser to access and retrieve files from a remote computer and to manage orcontrol files in a remote computer.

3. Mail services. This application provides the basis for e-mail forwarding andstorage.

4. Directory services. This application provides distributed database sourcesand access for global information about various objects and services.

10.6. INTERNETWORKINGInternetworking involves connecting two or more different computer networks or networksegments by a common routing technology. The result is called an internetworking asshown in Fig. 10.9.


The interconnection among or between public, private, commercial,industrial, or governmental networks may be defined as aninternetworking.

Fig. 10.9. Internetworking.

The simplest may simply involve two networks in nearest offices which are easilyconnected by using a bridge. More complex networks can be form by using routers orgateways. That links together network of different type of LANs or to interconnectLANs to a larger computer, such as a mainframe computer.

10.6.1. Type of InternetworkingThere are three type of internetworking, depending on who administers and whoparticipates in them:

1. Intranet. An intranet is a set of networks, using the internet protocol and IP-basedtools such as web browsers and file transfer applications, which are under the control ofa single administrative entity. Most commonly, an intranet is the internal network of anorganization. A large intranet will typically have at least one web server to provide userswith organizational information.

Intranets and extranets may or may not have connections to the Internet. If connectedto the Internet, the intranet or extranet is normally protected from being accessed fromthe internet without proper authorization.

L


2. Extranet. An extranet is a network or internetworking that is limited in scope to asingle organization. For example a company’s customers may be given access to somepart of its intranet.

3. Internet. The Internet is a specific internetworking. It consists of a worldwideinterconnection of governmental, academic, public, and private networks based upon thenetworking technologies of the internet protocol suite.

It is the successor of the advanced research projects agency network (ARPANET)developed by DARPA of the U.S. department of defense. The Internet is also thecommunications backbone underlying the world wide web (WWW).

10.6.2. Internetworking DevicesTo connect networks together we can use several devices. They are as follows:

1. Bridge

2. Router

3. Repeater

4. Gateway

5. Hub

6. Network Interface Card

1. Bridge. It is a network component that is used to connect two different types ofnetwork but it is compulsory that network operating system must be same type andsoftware should be same of both networks. This device is helpful to transfer data fromone network to other as shown in the Fig. 10.10.

Fig. 10.10. Bridge.


If one network is UNIX than other network is also be UNIX operating system. Protocolsare different for different operating system. But in bridge protocols must be same.

2. Routers. Router is a hardware device that enables which is the several possible pathsbetween source and destination. Routers are more sophisticated devices which work onthe network layer. (i.e. OSI model). It contains the software that helps in selecting bestpossible path for the particulars transmission. Router is also used to connect the twoLANS as shown in Fig. 10.11.

Fig. 10.11. Router.

The routing algorithm is that part of the network layer, responsible for deciding whichoutput line and incoming packet should be transmitted on.

3. Repeater. It is a network component as shown in Fig. 10.12. This component isworked on network. It is used to increase the frequency of signals. It increases thosefrequencies which are low.


Fig. 10.12. Repeater.

4. Gateway. A gateway is generally software which is installed within the routers. Thegateway understands the protocol used by each network link into the router and istherefore, able to translate from one into another.

Gateway is a protocol converter. A router transfers packet only across the networkusing similar type of protocols. But a gateway can accept a packet formatted for oneprotocol (Apple Talk) and convert it to a packet formatted for another protocol.

5. Hub. It is a hardware network component as shown in the Fig.10.13. This componentis used in start topology. With the help of hub we can connect node and servicesconnections. Today different sizes of hubs are available like 16 sokets, 24 sokets. Innormal hub a pin slot for the server and remaining for the node.

Fig. 10.13. Hub.


Through hub we also can identify which node is not working because each slot providesthe lighting facility. If light is not working is means particulars node is not working.

6. Network interface card (NIC). This card is fixed inside of CPU without this cardno computer can be connected with other. It is also called ethernet card as shown inFig. 10.14. It is necessary to install in computer then we can connect systems.

Fig. 10.14. Network Interface Card.

This card is fixed inside of CPU in all computers of networks.

10.7. TRANSMISSION CONTROL PROTOCOL /INTERNETPROTOCOL (TCP/IP)

First of all we should know what is protocol a why it is needed. The protocol is a set ofrules for communication. It is needed because you do not know the operating systemwhere you are communicating. Therefore based on type of hardware used to set ofrules for communicating two or more different devices.

In TCP/IP protocol TCP is a transport layer protocol and IP is a network layer protocol.TCP/IP evolved in a response to input from a wide variety of industry sources.Consequently TCP/IP is a most open of the protocol suits supported by the wide varietyof vendors. There are many different protocols defined in the Internet which comes inmodel called TCP/IP suite (Transmission control protocol / internet protocol) this suiteconsist of five layers as shown in Fig. 10.15.


Fig. 10.15. TCP/IP.

1. Physical layer

2. Data link layer

3. Network layer

4. Transport layer

5. Application layer

1. Physical layer. Physical Layer contains all the hardware devices, which helps in portabilityof data. The devices are as below:

1. Bridge

2. Router

3. Gateway

2. Data Link Layer. Data Link Layer helps in establishing link between two different data.It includes the following protocols.

(a) Post office protocol (POP). This protocol helps in working with E-mail. All uploadingand downloading works can be done with the help of this protocol.

3. Network layer. This layer helps in establishing network connectivity between twodifferent terminals. It includes the following protocols.

(a) Address resolution protocol (ARP). This protocol helps in converting internetaddress to hardware address.

(b) Reverse address resolution protocol (RARP). This protocol helps inconverting hardware address to internet address.


(c) Internet control message protocol (ICMP). This protocol is used to controlerrors and messages.

4. Transport layer. This layer helps in data transmission, which is in the form of packets.Protocols in this layer are as below:

(a) Transmission control protocol (TCP). This protocol is used in datatransmission. It works with the help of another protocol named IP (internetprotocol), which helps in gathering the address of machines connected to theinternet. TCP along with IP is called TCP/IP.

(b) User datagram protocol (UDP). This protocol helps in transmitting datagram(a package containing different information).

5. Application layer. This is the layer, which helps the users to interact with internet. Itcontains the following protocols:

(a) File transfer protocol (FTP). This protocol is used to transfer file from onesystem to another system.

(b) Simple mail transfer protocol (SMTP). This protocol is used for the purposeof electronic mail. Here only one-way communication is possible. That is can besend only but can not be received.

POINTS TO REMEMBER(i) We are using star topology in our labs.

(ii) Internet is network of networks.

(iii) Protocol is a set of rules to communicate with other devices.

(iv) Networking with in organization is called intranet.

(v) Networking of an organization which is located in different cities are calledinternet.

KEY TERMS❍ Networking ❍ Intranet Internet Protocol❍ Inter networking ❍ Extranet Topology Internet protocol❍ Transmission control protocol ❍ Local area network metropolital❍ Area network ❍ Wide area network

MULTIPLE CHOICE QUESTIONS1. LAN stands for?

(a) Large area network (b) Local area network(c) Large area networking (d) All of above


2. MAN stands for?(a) Metropolitan area network (b) Main area network(c) Manage area network (d) All of above

3. WAN stands for?(a) Wide area network (b) West area network(c) World are network (d) All of above

4. Which of the following is not network topology?(a) Ring topology (b) Star topology(c) Hash topology (d) Mesh topology(e) All of above

5. Which of the following is not type of internetworking?(a) Intranet (b) Extranet(c) Subnet (d) Internet

6. OSI stands for(a) Open system interconnection (b) Open system internetworking(c) Open style interconnection (d) None of above

7. How many layers have in OSI model?(a) 5 (b) 6(c) 7 (d) 8

8. TCP/IP stands for(a) Transmission control protocol/internet protocol(b) Transmission control protocol/international protocol(c) Truncate control protocol/internet protocol(d) None of above

9. How many layers have in TCP/IP model(a) 4 (b) 5(c) 6 (d) 7

10. The layer provides user interfaces and support for services is called(a) Application layer (b) Data link layer(c) Network layer (d) Physical layer

ANSWER1. (b) 2. (a) 3. (a) 4. (c) 5. (c)6. (b) 7. (c) 8. (a) 9. (b) 10. (a)

UNSOLVED QUESTIONS1. What is computer network ? Explain its goal.

2. Differentiate between LAN, WAN and MAN.


3. What is topology ? Define any four.

4. What is principle of OSI model ? Explain working of all layer.

5. What is the role function of session prerentation and application layer ?

6. How to configer a LAN in an organization ? List out the devices used.

7. Define following term :(a) Bridge(b) Router(c) Repeater(d) Gateway(e) Hub

(f) Network interface C and (NIC).

8. Define TCP/IP and its different layers.

9. Why TCP mouse with IP rather than UDP explain ?

10. Why ICMP need in IP ?

11. Explain protocol. What is the need of protocol in computer networks ?

❍ ❍ ❍

Computer Network By Pawan Thakur HOD CS & IT VIM BHOPAL

Education

Transcript of Computer Network By Pawan Thakur HOD CS & IT VIM BHOPAL