CSC 242 Introduction to

Telecommunications Systems

Dr. Ehsan MunirDepartment of Computer ScienceCOMSATS Institute of Information Technology

Lecture # 1

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What is CommunicationWhat is Communication When we communicate we share

information Local Communication

Face to face Remote Communication

Over distance

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DATA COMMUNICATIONSDATA COMMUNICATIONS

Data communicationsData communications are the exchange of data between are the exchange of data between two devices via some form of transmission medium such two devices via some form of transmission medium such as a wire cable. The word data refers to information as a wire cable. The word data refers to information presented in whatever form is agreed upon by the parties presented in whatever form is agreed upon by the parties creating and using the data. creating and using the data.

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Data Communication System For data communication to occur,

communicating devices must be a part of a system made up of some specific kind of hardware and software. This system is known as “DC System”

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DC System Components Message Sender Receiver Transmission Medium Protocol

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Figure Five components of data communication

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Factors Effecting DC System Delivery

Deliver data to correct destination Accuracy

Deliver data accurately Timeliness

Deliver data in a timely manner Jitter

Variation in packet arrival time

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Figure Data flow (simplex, half-duplex, and full-duplex)

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Data Flow Simplex

Transmission in one direction. Example Television

Half duplex Either direction, but only one way at a time.

Example Walkie-talkies Full duplex

Both directions at the same time. Example Phones.

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What is Telecommunication Tele is Greek word, meaning “far off” Webster calls it communications at a

distance The IEEE Standard Dictionary defines

telecommunications as the transmission of signals over long distance,

Science of communicating over distance

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Networks A network is a set of devices (nodes)

connected by communication links. A node can be a computer, printer, or

any other device capable of sending and/or receiving data generated by other nodes on the network.

A link is a communication pathway that transfers data from one device to another

Topology: Arrangement of nodes in a network specify topology.

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Figure Types of connections: point-to-point and multipoint

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Network Criteria Performance

Throughput: Number of bits transmitted in one second

Delay: How long it takes a bit of data to travel in network

Reliability Robustness : ability of the network to

perform its function in the face of attack (node failure)

Security Unauthorized access viruses

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Categories of topology

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Figure A bus topology connecting three stations

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Bus Topology Single cable connect all computers Each computer has connector to shared

cable Cable must end with a terminator Advantages

Ease of installation Inexpensive Works well for small networks

Disadvantages Cable break, whole network down Limited number of devices can be attached

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Figure A star topology connecting four stations

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Star Topology All computers attach to central point The devices are not directly linked to

one another Advantages

Ease of installation Inexpensive (less than mesh) Robustness

Disadvantages Hub fails, whole network down Costly than bus

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Figure A fully connected mesh topology (five devices)

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Mesh Topology Each device connected to every other

device Advantages

Robustness Can carry more data

Disadvantages Expensive Difficult to install Difficult to manage

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Figure A ring topology connecting six stations

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Ring Topology Each device connected to two devices

(immediate neighbors) The signal is passed along the ring in

one direction Advantages

Easy to install and reconfigure Inexpensive (less than mesh)

Disadvantages Break in a ring disables the whole network Unidirectional

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Figure A hybrid topology: a star backbone with three bus networks

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Types of Networks Local Area Network (LAN)

Links the nodes in a single office, building or campus

Wide Area Network (WAN) Links the nodes in states, countries or in the

whole world Metropolitan Area Network (MAN)

Between LAN and WAN Links the nodes in a town or city

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Protocols Protocol defines:

What is communicated How, it is communicated When, it is communicated

Elements of a protocol Syntax Semantics Timing

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Standards A standard provides a model for

development that makes it possible for a product to work regardless of the individual manufacturer

Standards are essential in: Creating/Maintaining open and

competitive market Guaranteeing National/International

Interoperability