lec-4 (protocol & its architecture)

Computer Communication and

Networks

Muhammad Waseem Iqbal

Data Communication Terminologies

Transmission System Utilization

We need to make efficient use of transmission facilities that are shared among a number of communicating devices.

For example:

Ϟ _{Techniques like Multiplexing to allow multiple users to share} total capacity of a transmission medium

Data Communication Terminologies

Interface

A device must have an interface with the transmission system/transmission medium.

Signal Generation

Ϟ Electromagnetic signals travel over transmission medium

Ϟ Once an interface is established, signal generation is required to communicate

Data Communication Terminologies

Synchronization

Ϟ The transmission and the reception should be properly synchronized Ϟ Synchronization means that the receiver must be able to determine

when a signal begins to arrive and when it ends

Ϟ It must also know the duration of each signal element

Ϟ In other words transmitter and receiver should have an agreement on the nature as well as timing of the signals

Exchange Management

If the data needs to be exchanged in both directions over a period of time, both parties must cooperate as follows:

Ϟ Whether both devices must transmit simultaneously or take turns Ϟ Amount of data to be sent at one time

Ϟ Format of the data

Data Communication Terminologies

Error Detection and Correction

Ϟ In all communication systems, there is a potential risk for errors and impairments

Ϟ Signals are distorted to some extent before reaching their destination

Ϟ Error detection & correction needs to be employed where a change in say, the contents of a file, cannot be tolerated

Flow Control

Ϟ To make sure that source does not overwhelm destination by sending data faster than it can be handled and processed

Recovery

Ϟ If a data transmission is interrupted due to a fault somewhere in the system, recovery techniques are needed

Data Communication Terminologies

Addressing & Routing

Ϟ If transmission facility is shared by two or more devices, source must specify the identity or the address of the destination system Ϟ And if transmission system is itself a system, a proper route must be

allocated that the data will take in order to reach the desired destination

Security

Security is very important issue in a Data Communication System. The sender needs to be assured that

Data Communication Terminologies

Message Format

Ϟ An agreement between two parties as to the form of the data to be exchanged or transmitted

Ϟ For example, both sides must use the same binary code for characters

Network Management

Ϟ A data communications facility is a complex system that cannot create or run itself

Data Communication Terminologies

Introduction to Protocol

A protocol is used for communication between entities in different systems.

Ϟ Entity is anything sending and receiving information

Ϟ Examples of entities are user application programs, file transfer packages, data-base management systems, electronic mail facilities, and terminals

Ϟ System is a physical object containing more than one entities

Protocol

Ϟ Now, two entities in different systems cannot just send data and expect to be understood

Ϟ For two entities to communicate successfully, they must "speak the same language.“

Ϟ For communication to occur, these entities must agree on a PROTOCOL

Protocol

As discussed earlier, “Protocol is a set of rules governing communication”.

Two computers cannot just send bit streams to each other and expect to be understood, they must agree on a protocol.

Example: French guy talking to a German Protocol defines:

Basic Elements Of Protocol

The key elements of a protocol are:

Syntax:

Structure or format of the data, meaning the order in which they are presented. For example, a simple protocol might

expect the first 8 bits of data to be the address of the sender, the

second 8 bits to be the address of the receiver, and the rest of the

stream to be the message itself.

Semantics:

Meaning of each section of bits. How is a particular pattern to be interpreted, and what action is to be taken based on

that interpretation? For example, does an address identify the

Basic Elements Of Protocol

Timing:

Refers to two characteristics; when data should be sent and how fast they can be sent. For example, if a sender produces

data at 100 Mbps but the receiver can process data at only 1 Mbps,

the transmission will overload the receiver and some data will be

Protocol Architecture

Ϟ The source system must either activate the direct data

communication path or inform the communication network of the

identity of the desired destination system

Ϟ The source system must ascertain that the destination system is

prepared to receive data

Ϟ The file transfer application on the source system must ascertain

that the file management program on the destination system is

prepared to accept and store the file for this particular user

Ϟ If the file formats used on the two systems are incompatible, one or

the other system must perform a format translation function

Protocol Architecture

Ϟ It is clear that there must be a high degree of cooperation between

the two computers

Ϟ Instead of implementing the logic for this as a single module, the

task is broken up into subtasks, each of which is implemented

Protocol Architecture

File transfer module:

Ϟ The file transfer module contains all of the logic that is unique to the

file transfer application, such as transmitting passwords, file

commands, and file records

Ϟ There is a need to transmit these files and commands reliably

Ϟ However, the same sorts of reliability requirements are relevant to a

Protocol Architecture

Communications service module:

Ϟ Therefore, these requirements are met by a separate

communications service module that can be used by a variety of

applications

Ϟ The communications service module is concerned with assuring that

the two computer systems are active and ready for data transfer

and for keeping track of the data that are being exchanged to assure

delivery

Ϟ However, these tasks are independent of the type of network that is

Protocol Architecture

Network access module:

Ϟ Therefore, the logic for actually dealing with the network is

separated out into a separate network access module

Ϟ That way, if the network to be used is changed, only the network

access module is affected