problem1. Illustrate out the functions of modulator and source encoder in digital communications system.

Quetsion2. By using suitable exs, make a distinction between the simplex and half duplex mode of communication.

problem3. In brief describe what is meant by physical topology of a network. Given that there are n devices in a network, what is the number of cable links required for following topologies?

(i) Mesh

(ii) Ring

(iii) Bus

(iv) Star

problem4. Determine which layer of the OSI model each of the 5 functions below is most likely to belong to. It is also possible that one or more of the functions cannot be mapped to OSI layer.  If this is the case, describe why.

i) Translating between EBCDIC to ASCII

ii) Defining the pin-outs in a connector employed to attach to a network cable

iii) Generating error correction codes for packet error correction

iv) Arbitrating between multiple nodes attached to single medium

v)  Providing an interface to visual packet monitoring program

problem5. Why is digital transmission better than analog transmission over long distance where repeaters are required in any case?  Give two merits of digital transmission over analogue transmission.

problem6. Assume that the length of a 10Base-5 cable is 2500 metres. If the speed of propagation in a thick co-axial cable is 60% of the speed of light, how long does it take for a bit to travel from the beginning to the end of the cable? Skip any propagation delay in equipment. (Speed of light = 3 x 10⁸ m/s)