COMP 327 Computer Networks Term Test I – October 12, 2007
1. (3 marks) Define the Internet correctly.
The network of networks, which uses TCP/IP protocol suite
2. (4 marks) What are the main responsibilities of the network layer and the data link layer?
Host-to-host delivery
Node-to-node delivery
3. (3 marks) The period of a signal is 200ns. What is its frequency in megahertz?
1/0.0000002 Hz = 5000000 Hz = 5 MHz
4. (10 marks) Assume we need to download 160 screens per minute. The resolution of the screen is
800 x 600 and the depth of each pixel is 1 byte. What is the required bit rate of the channel.
800 x 600 x 8 x 160 / 60
5. (10 marks) We have a channel with a 2 MHz bandwidth. The SNR for this channel is 62. What are the
appropriate bit rate and signal level? (C = B log2(1+SNR); R = 2 B log2L)
C = 2MHz x ln (1+62) is slightly smaller than 12 Mbps
R (= C) = 2 x 2MHz x ln L
=> ln L must be smaller than 3
=> Hence L is 4 and the bit rate is 2 x 2MHz x ln 4 = 8 Mbps
6. (10 marks) What are the propagation time and the transmission time for a 3 Kbyte message if the
bandwidth of the network is 100 Kbps? Assume that the distance between the send and the receiver
is 1,200 km and the light travels at 2.4 x 108 m/s.
Propagation time P = 1200000 / (2.4 x 100000000)
Transmission time T = 3000 x 8 / 100000 + P
7. (5 marks) We want to digitize the human voice of frequency 40 Hz – 4000 Hz. What is the bit rate,
assuming 32 bits per sample and the sampling rate of four times of the highest frequency?
4 x 4000 x 32
8. (10 marks) Draw the graphs of NRZ-L, NRZ-I, Manchester and AMI scheme for 00101110.
9. (10 marks) A corporation has a medium with a 20-MHz bandwidth. The corporation needs to create
10 separate independent channels each capable of sending at least 4 Mbps. The company has
decided to use QAM technology. We assume there is no guard band.
a. What kind of QAM has to be used?
b. What is the baud rate for each channel?
10. (5 marks) List three different types of address used in the Internet model, and explain how they are
used.
11. (10 marks) Explain the IP packet forwarding mechanism in the network layer at a router.