COMP 3270 Computer Networks
Term Test I – October 10, 2012
Student Number:
1.
Name:
(2 marks) We have a low-pass signal with a bandwidth of 4 KHz. We use 1024 quantization levels.
a) Calculate the sampling rate using the Nyquist theorem, not the Nyquist Bit Rate formula.
b) Calculate the bit rate of the digitized signal.
2.
(2 marks) When the Ethernet protocol decapsulates a network-layer packet, how does it know to which upper-layer protocol
(ARP or IP) the packet should be delivered?
3.
(2 marks) The attenuation of a signal is -20 dB. What is the original signal power if the final signal power is 4mW? (Note that
dB = 10 log10(P2/P1).)
4.
(2 marks) List the four address types in the Internet network model, with the corresponding layer in which each address type is
mainly used.
5.
(2 marks) The IP protocol entity running on a router received an IP packet that goes to another host computer system. List the
four steps used by the IP protocol entity to forward the IP packet to the next node.
6.
(2 marks) How many bits can fit on a link with 5 ms delay if the bandwidth of the link is 40 Mbps?
1(2): B
7.
(4 marks) A file contains 200 images and each image consists of 400 × 500 pixels. Each pixel uses 256 colours.
(a) What is the size of the file?
(b) If the bandwidth of a channel is 2048 Kbps, how long does it take to send this file?
8.
(4 marks) A 4-QAM signal uses the career frequency of 3000Hz to transmit 2000bps.
(a) What is the minimum bandwidth required by the 4-QAM signal? (Note that the minimum bandwidth required by ASK, PSK
or QAM is equal to the baud rate.)
(b) A medium can pass frequencies from 1500 to 3500 Hz (a bandwidth of 2000 Hz). Can the above signal faithfully pass
through this medium? Justify your answer. (Note that the composite signal produced by ASK, PSK or QAM equally spans
around the career frequency.)
9.
(4 marks) We need to send data at 4 Mbps rate.
(a) What is the minimum required bandwidth, using NRZ-L coding? (Note that the minimum bandwidth required by NRZ is
equal to the half of bit rate.)
(b) What is the minimum required bandwidth, using Manchester coding?
(c) What is the minimum required bandwidth, using the combination of 4B/5B and NRZ-L coding?
(d) List the two advantages of block coding.
2(2): B