Computer Networks

Data & Communication

When we communicate we share information Local Communication, if Face to Face Remote, if through Telephone etc

Data Information presented in any form that is agreed

upon by communicating parties. Text, Image, Video, Audio

Data Communication

Exchange of data between two devices via some form of transmission medium such as wire…

OR Data Communication is the exchange of information

from One entity to another using a transmission medium Exchange Information Entity Transmission Medium

Aims/Characteristics of Data Communication Delivery

Data should be delivered to the other party Addressing Mechanisms IP, MAC Address, Routing are used

to make delivery possible Accuracy

Data should not be corrupted during transmission Encoding, Error detection, Error recovery, Amplification of

signal Timeliness

Data should not be delivered after the time it is required. Quality of Service Support, Routing Protocols help in this

regard

Simplified Communication Model

Integral Parts of Communication Model… Source

Generates data to be transmitted Telephone, Mic, Computer, Web Cam, Scanner, Digital

Camera

Transmitter Data produced can not be transmitted directly Data should be converted to signals Transmitter converts data into transmittable

signals Modem converts Data Bits into Signals

Modulation

Integral Parts of Communication Model… Transmission System

It carries data from one party (sender) to another (receiver) Can be Wired / Wireless medium Can be complex network like Internet

Receiver It receives signal Converts received signal into data (bits)

Modem (demodulation)

Destination Takes incoming data from receiver.

Simplified Communication Model

Dial-up Internet Example

Key Tasks in Data Communication Optimal Transmission System Utilization

Efficient use of Medium Medium could be shared by many users Multiplexing could be implemented

Interfacing Connection of devices to Medium

Signal Generation Data Encoding Techniques How to represent data through signal Amplitude, Frequency, Phase???

Synchronization In synchronous communication Timing matters If sender sends the data and receiver is not ready/expecting,

data may be lost

Key Tasks in Data Communication Exchange Management

Connection Management How to establish, maintain and disconnect?

Error detection and correction Errors can occur in data during transmission Amount of error depends on medium / network

Damaged/Missed/Duplicated packets Some applications can tolerate errors (video/voice), others

can not (text/ email/ file) Mechanisms should be provided to detect and possibly

correct them or otherwise report them to sender

Key Tasks in Data Communication Flow Control

Communication of a device that produce data very fast with a device that accept data at low rate should be possible

Communication medium may not permit fast data transfer rate

We use some form of Flow Control to avoid data loss in such case

Techniques like Buffering may help Addressing and Routing

When more devices share a transmission medium, then we need addressing mechanisms to specify which device is destination

Routing is the selection of best path from sender to receiver

Key Tasks in Data Communication Recovery

If data transfer or a transaction is interrupted, how to recover from the damage

Disconnection from server during a file download! Message formatting

Agreed upon format for the message to be transferred Protocols/Standards

Key Tasks in Data Communication Security

To ensure that only the intended receiver actually receives the data

Even if the data is captured by some one else he should not be able to comprehend it

Network Management Network should be managed Access control Resource utilization Charges for use

Types of Communication/Directions of Data Flow Communication modes could be:

Simplex One Way (Uni directional) only One device is sender and other is receiver Monitor, Speakers etc Is Keyboard Simplex?

Half Duplex Bi-directional Only One device can send at a time and other will receive Traditional Wireless Sets

Full Duplex Bi-Directional Both Devices can send/Receive simultaneously Telephone Network

Need of Networking for Communication Point to point communication not usually

practical Devices are too far apart Large set of devices would need impractical

number of connections Solution is a Communications Network

Attach all devices to a communication network

Simplified Network Model

Classification of Networks

Networks are classified into two main categories: Local Area Network Wide Area Network

There are some more categories MAN, PAN etc

Local Area Network (LAN)

Smaller scope Building or small campus Usually owned by served organization/company

Data rates much higher Traditionally it used broadcast systems

instead of switched approach Now switched systems (Ethernet) and ATM (ATM

LANs) have replaced broadcasting hubs

Wide Area Networks (WAN)

Large geographical area Connect LANs Usually Public but may be Private Slower than LAN Consist of interconnected switching nodes

Nodes have no concern with data Just meant for providing switching facility toward

destination

A Typical Network Configuration

Network Implementation

Networks could be implemented in either Peer-to-Peer Configuration Client Server Configuration

Client Server Implementation Servers are distinguished from other systems which are known as

clients and all these are connected over a computer network Servers offer services which are used by client systems

Server serves clients Server always keep listening for clients A Server could be used for

Data Storage Distributed Application Resource Sharing Authorization Audit-ability Accountancy Security & easy Administration Centralized Control

A Server may require clients to log on before any services may be provided

Client Server Implementation

Client Server Implementation What is the difference in Servers and Clients

Physically Different Separate Kind of Machines?

Actual Difference in Software Server runs server software while client runs software

module (usually very small in comparison to server software)

Used Yahoo Messenger? You have a very tiny module of Yahoo Messenger (Clients) Actual Yahoo Messenger Server S/W is much heavy

Client Server Implementation (Advantages) Centralized Control Security Policies are easily implemented Logs could be create Reliability Easy to share resources Stable environment (Both H/W and S/W) Performance degrade gracefully in higher

loads

Client Server Implementation (Disadvantages) Costly to install Usually require Expert personnel to manage

Peer-to-Peer Networks

Each computer serves both as client as well as server

No centralized control for user access Usually useful for SOHO (Small Office/Home

Office)

Peer-to-Peer Networks

Peer-to-Peer NetworksAdvantages Easy to setup Low H/W, S/W cost Usually useful for file/print/internet sharing Useful in environments where security is not

an issue

Peer-to-Peer NetworksDisadvantages Not Reliable Performance degrade exponentially as new

nodes add into the network Compromised network security

Assignment 1

Write a brief report on different types of network implementation including WAN (Wide Area Network) LAN (Local Area Network) WLAN (Wireless Local Area Network) MAN (Metropolitan Area Network) SAN (Storage Area Network) CAN (Campus/Controlled/Cluster Area Network) PAN (Personal Area Network)