1. Powerpoint Templates Data Communication Muhammad Waseem Iqbal Lecture # 07 Spring-2016

2. Powerpoint Templates Acknowledgments These Lecture slides contain material from  Behrouz A. Forouzan, Data Communications and Networks, 4th Editionn and  William Stallings, Data & Computer Communication, 8 th edition

3. Powerpoint Templates 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: ϞTechniques like Multiplexing to allow multiple users to share total capacity of a transmission medium ϞCongestion Control is used so that the receiver should not be overwhelmed by data/traffic

4. Powerpoint Templates Data Communication Terminologies Interface A device must have an interface with the transmission system/transmission medium. Signal Generation ϞElectromagnetic signals travel over transmission medium ϞOnce an interface is established, signal generation is required to communicate ϞSignals are capable of being propagated over transmission medium interpretable as data at the receiver

5. Powerpoint Templates Data Communication Terminologies Synchronization ϞThe transmission and the reception should be properly synchronized ϞSynchronization means that the receiver must be able to determine when a signal begins to arrive and when it ends ϞIt must also know the duration of each signal element ϞIn 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: ϞWhether both devices must transmit simultaneously or take turns ϞAmount of data to be sent at one time ϞFormat of the data ϞWhat to do when an error occurs

6. Powerpoint Templates Data Communication Terminologies Error Detection and Correction ϞIn all communication systems, there is a potential risk for errors and impairments ϞSignals are distorted to some extent before reaching their destination ϞError detection & correction needs to be employed where a change in say, the contents of a file, cannot be tolerated Flow Control ϞTo make sure that source does not overwhelm destination by sending data faster than it can be handled and processed Recovery ϞIf a data transmission is interrupted due to a fault somewhere in the system, recovery techniques are needed ϞThe objective is either to resume activity at the point of interruption and to restore the state of the system to what it was prior to the interruption

7. Powerpoint Templates Data Communication Terminologies Addressing & Routing ϞIf transmission facility is shared by two or more devices, source must specify the identity or the address of the destination system ϞAnd 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 ϞOnly the intended receiver receives the data ϞData is delivered unaltered

8. Powerpoint Templates Data Communication Terminologies Message Format ϞAn agreement between two parties as to the form of the data to be exchanged or transmitted ϞFor example, both sides must use the same binary code for characters Network Management ϞA data communications facility is a complex system that cannot create or run itself ϞNetwork management capabilities are needed to configure the system, monitor its status, react to failures and overloads, and plan intelligently for future growth

9. Powerpoint Templates Data Communication Terminologies Introduction to Protocol A protocol is used for communication between entities in different systems. ϞEntity is anything sending and receiving information ϞExamples of entities are user application programs, file transfer packages, data-base management systems, electronic mail facilities, and terminals ϞSystem is a physical object containing more than one entities ϞExamples of systems are computers, terminals, and remote sensors

10. Powerpoint Templates Protocol ϞNow, two entities in different systems cannot just send data and expect to be understood ϞFor two entities to communicate successfully, they must "speak the same language.“ ϞFor 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: ϞWhat is Communicated? ϞHow it is Communicated? ϞWhen it is Communicated?

11. Powerpoint Templates 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 route to be taken or the final destination of the message? It includes control information for coordination and error handling.

12. Powerpoint Templates 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 lost. It includes speed matching and sequencing.

13. Powerpoint Templates Protocol Architecture ϞThe source system must either activate the direct data communication path or inform the communication network of the identity of the desired destination system ϞThe source system must ascertain that the destination system is prepared to receive data ϞThe 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 ϞIf the file formats used on the two systems are incompatible, one or the other system must perform a format translation function ϞSo, the file transfer task although look simple, involves a complex logic between the two end systems.

14. Powerpoint Templates Protocol Architecture ϞIt is clear that there must be a high degree of cooperation between the two computers ϞInstead of implementing the logic for this as a single module, the task is broken up into subtasks, each of which is implemented separately

15. Powerpoint Templates Protocol Architecture File transfer module: ϞThe 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 ϞThere is a need to transmit these files and commands reliably ϞHowever, the same sorts of reliability requirements are relevant to a variety of applications (e.g. electronic mail, document transfer)

16. Powerpoint Templates Protocol Architecture Communications service module: ϞTherefore, these requirements are met by a separate communications service module that can be used by a variety of applications ϞThe 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 ϞHowever, these tasks are independent of the type of network that is being used

17. Powerpoint Templates Protocol Architecture Network access module: ϞTherefore, the logic for actually dealing with the network is separated out into a separate network access module ϞThat way, if the network to be used is changed, only the network access module is affected Thus, instead of a single module for performing communications, there is a structured set of modules that implements the communications function. That structure is referred to as a protocol architecture