Digital Communication

Lecturer: Professor I.M. Leslie

No. of lectures: 12

This course is a prerequisite for Distributed Systems.

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. Shared media networks with particular emphasis on media access control. Packet scheduling. Non orthogonal multiplexing. Multiplexing and channel characteristics.

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

• 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.

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

• The Internet Internet architecture, context of development, addressing and routing, transmission control protocol (TCP), higher layer protocols, evolution.

• 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

• have an informed view of the internal workings of the Internet

Recommended books

* Peterson, L.L. & Davie, B.S. (2003). Computer networks: a systems approach. Morgan Kaufmann (3rd ed.).
Comer, D. & Stevens, D. (1995). Internetworking with TCP-IP, vol. 1 and 2. Prentice-Hall (3rd ed.).
Schwartz, M. (1987). Telecommunication networks: protocols, modeling and analysis. Addison-Wesley.