ELE3040
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ELE3040
Q1. (a) An Ethernet router has a single outgoing transmission link of 12 Mbps. The average length of each packet is 720 bytes. If the average packet delay through the switch, is to be less than 15 ms, assuming an M/M/1 queue determine:
(i) the departure rate in packets/s;
(ii) the maximum gross input packet rate to the switch in packets/s; (iii) the average length of the queue.
(b) A 20Mbps link is to be set up between an imaging system deployed on the moon and a control centre on the earth. The distance from the earth to the moon is approximately 385,000km, and data travels over the link at the speed of light (c = 3x108 m/s). Assume that there is no packetisation and the images are sent in digital format in one transmission, upon reception of a download command from the control centre.
(i) Calculate the minimum RTT for the link.
(ii) Calculate how much data a transmitter on the moon can send, before it is possible to receive a response from the earth.
(c) If datagrams are sent using IP packets of fixed size 1492 bytes, compare the percentage overhead incurred by using basic IPv4 (with no options field) and IPv6 (with no next hop header).
(d) Consider a sender S and a receiver R that are connected on a network where the one-way latency is 200 ms (milliseconds), that the data rate is 16,000 bits/s (bits per second), and that each frame is 1,000 bits. Assume that S and R are using sliding windows with selective repeat.
(i) How large must the window for S be in order to maximize utilization?
(ii) Based on that window size, how many bits must be used in each frame as a frame identifier (that is, a frame number)?
Q2. (a) We consider a cellular network with a transmit power of 1.75W. The transmit and receive antenna gains are equal to 3.5, while the operating carrier frequency is 6 GHz. If the receiver bandwidth is 20KHz and the noise figure is 9 (linear scale), determine the maximum distance to support a SNR of 25dB.
(Hint: Assume free-space propagation, no error losses and that the reference distance is 1km)
(b) A series of 500 bit frames have to be transmitted across a microwave data link 60km in length at a data rate of 25Mbps. Assuming the link has a bit error rate of 4 x 10-5, and a velocity of propagation v = 3 x 108 m/s, determine the link utilisation efficiency using the following protocols:
(i) Idle RQ
(ii) Selective repeat RQ with a send window buffer k=2.
(iii) Suggest a way to increase the link utilisation of the Selective repeat RQ scheme. Discuss potential disadvantages of such an approach.
(c) In a cellular network, the Signal/Interference ratio requirement is 8dB. What is the recommended number of cells, assuming that the path-loss exponent is equal to 3. Also, describe the frequency reuse concept.
2023-12-15