TCOM 551 & ECE 463 homework No. 4 February 2008.doc

TCOM 551 and ECE 463 ? Spring 2008 Homework No. 4 Set: February 12th, 2008 Due: February 19th, 2008 ????????????????. Print name Last four digits of your SID Number (a) Name the three fundamental voice-signal quality parameters defined by the CCITT (now ITU-R) and the minimum values these parameters must have to meet performance criteria. (3 points) Answer: (b) What, approximately, is the acceptable minimum S/N ratio in dB for an analog TV? (2 points) Answer: (c) What, approximately, is the acceptable minimum S/N ratio in dB for uncoded digital TV, assuming a minimum BER of 10-6 is required? (2 points) Answer: (a) What is Layer 3 in the traditional ISO-OSI stack? (2 points) Answer: (b) Why is layer 3 more complex when mobile communications systems are involved? (2 points) Answer: (c) Explain the difference between connection oriented and connectionless operations. (2 points) Answer: (d) Why is frame relay generally faster than X.25? (2 points) Answer: (e) In what way are Communications and Network Security Issues affecting the choice between circuit switched and packet switched delivery? (2 points) Answer: (f) A BER of 10-3 is normally considered to be the worst BER that a digital voice circuit can tolerate for acceptable performance. Why is it then that some current digital voice links are required to maintain a BER of 10-5 in order not to have an outage? (2 points) Answer: (a) What is TDD (both what the acronym means and how it works; 2 points each)? (4 points) Answer: (b) How can TDD affect delay in a circuit? (4 points) (c) What is an Input DEMUX and an Output MUX, and what do they do? (4 points) Answer: (d) Why were long distance, two-wire, analog telephone connections not possible? (4 points) Answer: (e) What was the earliest form of analog multiplexing? (2 points) Answer: (f) How many individual analog voice channels are there in a Super Group? (2 points) Answer: (g) What is WDM (state what the acronym is and what it means)? (3 points) Answer: (h) Why would you need something like a distributed feedback laser in a WDM system? (4 points) Answer: (i) What does the acronym DWDM stand for and why would you employ DWDM in an optical communications system? (4 points) Answer: (j) Explain why you cannot add modulation after multiplexing in a WDM or DWDM system that employs on-off keying. (3 points) Answer: (k) What does the acronym TASI stand for? (2 points) Answer: (a) What is Statistical Multiplexing? (5 points) Answer: (b) A supplier of digital voice circuits has to decide how many equivalent 64 kbit/s voice circuits to install between a large new sub-development and the nearest switching office. Each user wants to have a voice circuit only (no data transmitted). The supplier plans to install a statistical multiplexer within the sub-development and to provide a digital voice circuit to each home. (i) If there are 8,000 homes, how many equivalent 64 kbit/s voice circuits are required if no statistical multiplexing is performed and no low rate encoding is carried out on the voice circuits from the homes? (5 points) Answer: (ii) If 2.5:1 DSI is carried out by the statistical multiplexer, how many 64 kbit/s equivalent voice circuits are required now? (5 points) Answer: (iii) If 8 kbit/s LD-CELP is introduced, in addition to the 2.5:1 DSI, how many 64 kbit/s equivalent voice circuits are required now? (5 points) Answer: (a) What is jitter in a digital signal? (3 points) Answer: (b) If an OC-192 signal has a maximum jitter that is equivalent to one quarter of a bit period, what is this equivalent to in time? Give your answer in picoseconds (4 points) Answer: (c) If the receive clock can accommodate timing jitter of 32 ps, can this receiver work with the jitter in part (b) above? (3 points) Answer: (a) What is a Pleisiochronous Network? (3 points) Answer: (b) How can Synchronous, Asynchronous, and Pleisiochronous Networks work together? (4 points) Answer: (a) What does the acronym UWB stand for? (2 points) Answer: (b) Explain briefly how does a UWB communications system work? (3 points) Answer: (c) What are at least three challenging technical elements that need to be resolved to make UWB accepted worldwide? (3 points) Answer: PAGE PAGE 1