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/ / 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

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 Networks Advantages 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 Networks Disadvantages 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)