Digital Communication

Lecturer: Professor I.M. Leslie (iml@cl.cam.ac.uk)

No. of lectures: 12

This course is a prerequisite for Distributed Systems (Diploma).

Aims

The aims of this course are to develop an understanding of communications networks from a wide perspective, within a framework of principles rather than technologies or architectures. Technologies and architectures will, however, be used as examples and motivation.

Lectures

• Scope. Two example systems: Ethernet and the telephone system: basic operation; common issues; differing constraints; differing approaches.

• Partitioning the problem. Abstraction, service versus implementation; layering as a restricted form of abstraction; motivation for layering; the channel as an abstraction; layered channels.

• Fundamental transmission. Emphasis on the service provided by physical channel; limitations: noise, attenuation. Channel capacity (bandwidth). Modulation techniques for digital systems.

• Coding. Coding as a general concept: modulation as a form of coding, A-D-D-A, error correcting and detecting codes, other forms of coding, relation to layering.

• Multiplexing. Basic definitions, FDM, synchronous and asynchronous TDM. Circuit switching, packet switching, ATM. Local area networks with particular emphasis on media access control.

• Switching and routing. Introduction from LAN perspective (repeaters, bridges, routers). Fundamental view of switching extended to telephone network, connectionless versus connection oriented.

• Naming, addressing and routing. Service access points, binding. Hierarchical versus flat address spaces. Routing classifications and algorithms.

• Protocols and state. Imperfect view of state at far end of channel. ARQ as an example of an error control protocol; sliding window ARQ as an example of a flow control protocol; flow control in general: X.25 as an example.

• Standards. Role of standards, dynamics of standards process, standards bodies.

Objectives

At the end of the course students should

• be able to analyse a communication system by separating out the different functions provided by the network

• understand that there are fundamental limits to physical transmission systems

• understand the general principles behind multiplexing, addressing, routing and stateful protocols as well as specific examples of each

• understand what FEC is and how CRCs work

• be able to compare communications systems in how they solve similar problems

Recommended books

Comer, D. & Stevens, D. (1995). Internetworking with TCP-IP, vol. 1 and 2. Prentice-Hall (3rd ed.).
Halsall, F. (1992). Data Communications, Computer Networks and Open Systems. Addison-Wesley (3rd ed.).
Schwartz, M. (1987). Telecommunication Networks: Protocols, Modeling and Analysis. Addison-Wesley.