Bismillah-Hir-Rahman-Nir-Raheem “DATA COMMUNICATIONS AND COMPUTER NETWORKS” By: Md.Rahmathullah, Assistant Prof., M.J.C.E.T.
Text Books & References • William Stallings – Data & Computer Communications, 6th Edition. • Forouzan – Data Communications and Computer Networks. • Tanenbaum – Computer Networks. WEB: www.rahmath.tk www.freewebs.com/rahmath/
Introduction to Data Communication: • Data Communication is the process of transferring digital information in the binary form between two or more points.
Applications: • Data Communications is the most imp. Communication Today. It is used in: • ATMs in banking industry • Communications • Multimedia • Mass media • News gorups • Railway reservations • Airway reservation • E-mail, Internet…many more
Various components of a Data Communications system: 1 Protocol 2 …… 3 …… 1 Protocol 2 ….. 3 ….. Message RECEIVER SENDER
Important components of any Data Communication system are: • MESSAGE. • MEDIUM. • SENDER. (a digital computer with necessary accessories) • RECEIVER (a digital computer with necessary accessories) • PROTOCOL ( governs the way the communication has to take place between sender and receiver) Note: For Data Communication to occur the communicating devices must be a part of the communication system.
Fundamental Characteristics of Data Communication system: • DELIVERY • ACCURACY • TIMELINESS • (Real-Time transmission)
Typical Computer N/W or Data Commn. N/W: Links Node Node
Network Criteria: Data Communication N/W Criteria Security Performance Reliability
Performance: • Measured in terms of Transit time and Response time. Transit time Amount of time required for a message to travel from one device to another. Response time Elapsed time b/n an enquiry and response.
Performance….. • Other factors on which performance of a network depends is: • No. of Users ( As No of users , Response time implies performance ) • Type of txn media (Parallel wires, co-axial cables,fibre optic cables,etc) • H/w. ( A higher speed computer with large storage capacity provides better performance) • S/w ( It is used to process data at the sender, receiver and at intermediate nodes. The data has to be transformed in to transmittable signals)
Reliability: • Frequency of failure (How often the n/w fails) • Recovery time if the link fails • Robustness of network in case of Catastrophe i.e fires, accidents, earth quakes etc)
Security: • Protecting data from unauthorized access • Viruses Remedy: Use Password (at the lowest level) Use encryption- decryption techniques Use h/w & s/w specifically for avoiding viruses.
Protocols:- • Need for protocol: In any computer network, Commn occurs b/n entities of different systems. An entity is anything capable of sending or receiving information. Ex: Application programs, File transfer packages, Browsers, DBMS, e-mail s/ws.
Need for Protocol…………. • A system is a physical object that contains one or more entities. Ex: Computers & terminals. Two entities cannot just send bits of streams to each other and expect to be understood. For Commn to occur both the entities must agree on a protocol.
A Protocol: • Thus we can say a Protocol defines What is Communicated? How it is Communicated? When it is Communicated?
Key elements of a protocol / Protocol elements: • Syntax • Semantics • Timing
Syntax: Syntax refers to the structure or format of the data, meaning the order in which they are presented. • Semantics: Refers to the meaning of each section of bits. How the particular pattern is to be interpreted ,etc. • Timing: Timing refers to two characteristics: When data should be sent? & How fast the data should be sent?
Def: of Protocol • Protocol is set of rules or conventions that govern all the aspects of information communication.
STANDARDS: • Necessity of Standard: Imagine what happens if the best components we need are not made by the same company…………….. …The components will not understand one another. Therefore standards are required.
Standard • A standard provides a model for development that makes it possible for a product to work regardless of the individual manufacturer. • Provides inter-operability of data & telecomm b/n nations. • Provides guidelines to manufacturers, vendors, govt. agencies, etc.
STANDARDS De Jure (By Law) De Facto ( By Fact)
Some standards for Data commn are: • ISO – International Standard Organization • ITU-T (CCITT) – International Telecom Union –Telecom std. • ANSI - American National Standard Institute • IEEE – Insti……. • EIA - Electronic Industries Association • TELECORDIA