Question 1

(a) Describe the functions of the modulator and source encoder in a digital communications system.

(b) By using appropriate examples, distinguish between the simplex and half duplex mode of communication.

(c) Briefly illustrate what is meant by the physical topology of a network. Given that there are n devices in a network, what is the number of cable links required for the following topologies:

(i) Mesh
(ii) Ring
(iii) Bus
(iv) Star

(d) Identify which layer of the OSI model each of the five functions below is most likely to belong to. It is also possible that one or more of the functions cannot be mapped to an OSI layer. If this is the case, explain why.

(i) Translating between EBCDIC to ASCII
(ii) Defining the pin-outs in a connector used to attach to a network cable
(iii) Generating error correction codes for packet error correction
(iv) Arbitrating between multiple nodes attached to a single medium
(v) Providing an interface to a visual packet monitoring program

(e) Why is digital transmission better than analog transmission over a long distance where repeaters are needed in any case? Give two advantages of digital transmission over analogue transmission.