Introduction to Computer Networks

Networks

A A networknetwork is a set of devices (often referred to as is a set of devices (often referred to as nodesnodes) connected by communication ) connected by communication linkslinks. A node can . A node can be a computer, printer, or any other device capable of be a computer, printer, or any other device capable of sending and/or receiving data generated by other sending and/or receiving data generated by other nodes on the network.nodes on the network.

Introduction to Computer Networks

By: Jigar M. Pandya

Rules For CommunicationIntroduction to Computer Networks

Transmission should take place without error.

Transmission should be Less.

The cost of Transmission should be less.

The message should be safe and secure.

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5 Components For Communication

Introduction to Computer Networks

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Data Flow Of MessagesIntroduction to Computer Networks

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Applications of Networks

Resource SharingHardware (computing resources, disks, printers)Software (application software)

Information SharingEasy accessibility from anywhere (files, databases)Search Capability (WWW)

CommunicationEmailMessage broadcast

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Network Topology

The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions.

Introduction to Computer Networks

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Bus Topology

Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable.

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Star & Tree TopologyThe star topology is the most commonly used architecture in Ethernet LANs.

Larger networks use the extended star topology also called tree topology. When used with network devices that filter frames or packets, like bridges, switches, and routers, this topology significantly reduces the traffic on the wires by sending packets only to the wires of the destination host.

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Ring TopologyA frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame.

The frame then continues around the ring until it finds the destination node, which takes the data out of the frame.

Single ring – All the devices on the network share a single cable

Dual ring – The dual ring topology allows data to be sent in both directions.

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Mesh Topology

The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance.

It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions.

Implementing the mesh topology is expensive and difficult.

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Types of Connection

Introduction to Computer Networks

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Network Components

Introduction to Computer Networks

Physical Media

Interconnecting Devices

Computers

Networking Software

Applications

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LAN, MAN & WAN

Network in small geographical Area (Room, Building or a Campus) is called LAN (Local Area Network)

Network in a City is call MAN (Metropolitan Area Network)

Network spread geographically (Country or across Globe) is called WAN (Wide Area Network)

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Applications

E-mailSearchable Data (Web Sites)E-CommerceNews GroupsInternet Telephony (VoIP)Video ConferencingChat GroupsInstant Messengers Internet Radio

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Network Models

Two Types Of Connections are there Connection Oriented service Connectionless service1. Connection Oriented Service.

Similar to the telephone system1. Establish Connection 2. Use Connection 3. Release connection.

2. Connectionless service. Same as postal service, each message has full add. Order may differ of delivery. Five primitives are used.1. Listen 2. Connect3. Receive4. Send5. Disconnect

LAYERED TASKSLAYERED TASKS

We use the concept of We use the concept of layerslayers in our daily life. As an in our daily life. As an example, let us consider two friends who communicate example, let us consider two friends who communicate through postal mail. The process of sending a letter to a through postal mail. The process of sending a letter to a friend would be complex if there were no services friend would be complex if there were no services available from the post office. available from the post office.

Tasks involved in sending a letter

THE OSI MODELTHE OSI MODEL

Established in 1947, the International Standards Established in 1947, the International Standards Organization (Organization (ISOISO) is a multinational body dedicated to ) is a multinational body dedicated to worldwide agreement on international standards. An ISO worldwide agreement on international standards. An ISO standard that covers all aspects of network standard that covers all aspects of network communications is the Open Systems Interconnection communications is the Open Systems Interconnection ((OSIOSI) model. It was first introduced in the late 1970s. ) model. It was first introduced in the late 1970s.

ISO is the organization.OSI is the model.

Seven layers of the OSI model

The interaction between layers in the OSI model

Physical layer

The physical layer is responsible for movements ofindividual bits from one hop (node) to the next.

Data link layer

The data link layer is responsible for moving frames from one hop (node) to the next.

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Figure 2.7 Hop-to-hop delivery

Network layer

The network layer is responsible for the delivery of individual packets from

the source host to the destination host.

Transport layer

The transport layer is responsible for the delivery of a message from one process to another.

Session layer

The session layer is responsible for dialog control and synchronization.

Presentation layer

The presentation layer is responsible for translation, compression, and encryption.

Presentation layer

• Data translation ,compression and encryption.• Encrypt data to hide it.• Compress data from last message to small no of

messages.

Application layer

The application layer is responsible for providing services to the user.

Application layer

• Login password checking, file transfer are some of the application.

• Provide direct access to network device.• Interface between user and system.

Examples• File transfer• Emails• www

• Protocols• ftp, smtp, telnet….

Summary of layers

QUESTIONS

1. What is Connection Oriented Service ?2. What Is Connection Less Service ?3. Example Of Connation Less ?4. Example Of Connection Oriented ?5. Full Form Of OSI 6. Full Form OF ISO7. What is OSI Model ?8. How many Layers are there in OSI Model ?9. Task Of Application layer ?10. Task Of Presentation layer ?11. Task Of Session layer ?12. Task Of Transport layer ?13. Task Of Network layer ?14. Task Of Data-link layer ?15. Task Of Physical layer ?

TCP/IP ModelTCP/IP Model

The layers in the The layers in the TCP/IP MODEL TCP/IP MODEL do not exactly match do not exactly match those in the OSI model.those in the OSI model.

The original TCP/IP protocol suite was defined as The original TCP/IP protocol suite was defined as having four layers: having four layers: host-to-networkhost-to-network, , internetinternet, , transporttransport, , and and applicationapplication. .

However, when TCP/IP is compared to OSI, we can say However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: that the TCP/IP protocol suite is made of five layers: physicalphysical, , data linkdata link, , networknetwork, , transporttransport, and , and applicationapplication..

TCP/IP ModelTCP/IP Model( Transmission control protocol / internet protocol )

The TCP/IP reference model.

TCP/IP ModelTCP/IP Model

• IT Was earlier used by ARPA(Advanced Research Project Agency)

• Used to connect Military networks together.

• Basically work for the internet .

• TCP/IP offers a simple naming and addressing scheme.

• Info is carried in packets.

• IP is used to put message in Packet.

• Each packet has address of sender and receiver (IP Address)

• Divide large message in to small packets.

• It is not necessary for all packets to follow same route.

• HTTP helps it to Share HTML Doc with the help of WWW.

( Transmission control protocol / internet protocol )

TCP/IP Model LayersTCP/IP Model LayersHost – to – Network LayerHost – to – Network Layer

• Lowest Layer in model

• Combination of Physical and Data-link Layer.

• The host has to connect to the network using some protocol, so

it can send IP packets over it.

• Protocol may vary based on host or network.

TCP/IP Model LayersTCP/IP Model LayersInternet LayerInternet Layer

• It holds whole architecture together.

• The task is to insert packet into any network and make them

travel.

• The order of packets may differ ,the higher layer support it to

arrange packets.

• It Defines Packet format and protocol called IP.

• Routing of packets and congestion control are important issues.

• Almost same as the network layer in OSI model.

TCP/IP Model LayersTCP/IP Model LayersTransport LayerTransport Layer

• Same Function as Transport layer in OSI layer.

• It allows entities to converse with each other.

• The Protocols Used Are TCP & UDP.

• TCP is Connection Oriented Service, No Error ,Handles Flow

of control.

• UDP is Connection less service, Chances Of Error , Prompt

delivery is more important then accurate.

TCP/IP Model LayersTCP/IP Model LayersApplication LayerApplication Layer

• IT Doesn't Have Session or Presentation Layer.

• All upper level protocols are supported by This layer.

• Main task is to provide user interface.

• Provide services that can be used by other services.

• For Example .

• SMTP :- Mailing Service

• Telnet :- Remote Logon Service

• FTP :- File Transfer Service.

TCP/IP and OSI model

Comparing OSI and TCP/IP Models

Concepts central to the OSI model• Services• Interfaces• Protocols

Comparing OSI and TCP/IP Models

Why OSI did not take over the world• Bad timing• Bad technology• Bad implementations• Bad politics

Comparing OSI and TCP/IP Models

Problems In TCP / IP :• Service, interface, and protocol not distinguished• Not a general model• Host-to-network “layer” not really a layer• No mention of physical and data link layers• Minor protocols deeply embedded, hard to

replace

Hybrid Model

• Addressing - whom am I going to talk to? i.e., how do we identify

senders and receivers?

• Rules for data transfer: Simplex ,half-duplex and full duplex

• Error control: This is all about communicating along imperfect

channels and error correction in such cases.

• Large messages: Procedures for disassembling, transmitting and

reassembling.

Design Issues For Layers