Computer NetworksECS-601

References Forouzen, "Data Communication and Networking", TMH

A.S. Tanenbaum, Computer Networks, Pearson

Education W. Stallings, Data and Computer Communication, Macmillan Press Anuranjan Misra, Computer Networks, Acme Learning G.Shanmugarathinam,Essential of TCP/ IP, Firewall Media S. Keshav, An Engineering Approach on Computer

Networking, Addison Wesley

What is a network??

Network a collection of people or things focused on a common

goal Examples Telephone Hospital Railways Friends Social Relatives etc. means an interconnected set of some objects

Computer Network

A computer network is an interconnection between

general purpose programmable devices that deals with the handling of data. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other A computer network is the infrastructure that allows two or more computers (called hosts) to communicate with each other.

Computer Network A computer network is a collection of a number of

computers (also called nodes), connected through some communication lines. Two computers connected to a network can communicate with each other through other nodes if they are not directly connected. Some of the nodes in the network may not be computers at all but they are network devices(like switches, routers etc.) to facilitate communication.

Uses of computer network Exchange of information between different

computers. Interconnected small computers in place of large computers. Communication tools.

Modes of communicationPoint to point

Broadcasting

Multicasting

Point To Point(Data Flow) Dedicatedo Simple o Full duplex o Half duplex

Sharedo Multiplexing

Simplex

Half-Duplex

Full-duplex

Broadcast Network

Classification(Categories) Local area network(LAN)

Privately owned Restricted in size Bigger size Access issues(because of cost) Cost Internetwork

Metropolitan Area Network(MAN)

Wide Area Network(WAN)

LAN

MAN

WAN

Goals Of Computer Network Resource sharing Load sharing High reliability Cost effectiveness Scalability

Powerful communication medium Easy accessibility from anywhere (files, databases) Search Capability (WWW) Remote computing Distributed processing And many more

Network Applications Access to remote information Person-to-person communication Interactive entertainment

Applications contd.

Sales Financial Service Manufacturing E-mail Directory Services Information Services Searchable Data (Web Sites) E-Commerce EDI EFT Tele Conferencing Voice Conferencing Video Conferencing Cellular Telephone Cable Television Internet Telephony Chat Groups Instant Messengers Internet Radio

Client-Server Model

Client Server Model One PC per user

Data resides on remote server, that is shared among all

the users. Users are called clients. E.g.- employees accessing companys information system.

Data Communication Network

Data Communication Effectiveness of data communication network

depends upon Delivery Accuracy Timeliness Jitter

Components Of a Communication Network

5. Protocol

4. Medium 2. Sender 1. Message 3. Receiver

Protocol Represents an agreement between communicating entities Special set of rules that end points use when they

communicate An agreed-upon format for transmitting data between two

devices The rules that govern a specific layer of communication A set of rules that make communication more efficient Allows data packets to travel from source to destination without misunderstanding

Formal DefinitionA predefined set of rules, or an agreements, that determine the format and transmission of data

Key Elements Of A Protocol Syntax Structure or format of data

Semantics Meaning of each section Interpretation and action to be taken

Timing When data should be sent How fast data can be sent

Protocol Interfaces These are building blocks of a network architecture Each protocol object has two different interfaces Service Interface Defines operations on this protocol Peer to peer Interface Defines messages exchanged with peers.

Protocol HierarchyN+1 N+1

N

N

N-1

N-1

Most networks are organized as a series of layers The task of each layer is to give some service to

the upper layer. Any layer maintains a virtual connection with the corresponding layer in the peer.

There is a peer to peer protocol running between

any two corresponding and communicating layers. The interface between the layers in the same node is well defined. The implementation of each layer in each node is transparent to other nodes.

Data Representation Text Sequence of bits

Numbers Bit patterns Directly converted to binary number

Images Matrix of pixels Each pixel has a bit pattern

Audio Continuous in nature

Video

Network Criteria Performance Reliability Security

Network Topologies The physical structure of the network devices. the way that the devices on a network are arranged

and how they communicate with each other The way each node is physically connected to the network

Types of TopologiesPhysical Topology The way the nodes are

Logical Topology The way the data passes

connected to the network through the actual cables The way in which the network is laid out physically

through the network from one node to other The way in which the

network is laid out electrically

Physical TopologiesBus Extended Star

Ring

Hierarchical

Star

Mesh

Mesh TopologyEvery device has a dedicated point-to-point link to every other device.

Advantages and Disadvantages Advantages Elimination of traffic problems Robust in nature Privacy and security Easy fault detection and isolation

Disadvantages Cost of cabling Space

If there are n nodes, No. of communication links=n(n-1)/2 No. of I/O ports= (n-1)

Example- Telephone regional Offices.

Bus Topology(Linear cable)

It is multipoint in nature One cable acts as a backbone to connect all the devices in a

network. Only one host can transmit at a time Decentralized control All hosts directly connected to the backbone.

Advantages and Disadvantages Advantages Ease of installation Less cabling required

Disadvantages Fault isolation Adding new nodes is difficult Single link failure

Star Topology

All device connected to a central point, not

directly connected to each other Center of star is usually a hub or a switch

Advantages and Disadvantages Advantages Less expensive Easy to install and reconfigure Robustness Easy fault identification and isolation

Disadvantages Single point of failure One cable from each node to hub

Ring Topology A host is directly connected to each of its

neighbors Data flow in one direction No backbone Broadcast system

Ring Topology

Advantages and Disadvantages Advantages Easy to install and configure No collision Low cost Easier to find faults

Disadvantages A break in the ring will bring it down Node failure causes network failure