UNIVERSITY OF CAPE TOWN
Department of Electrical Engineering
EEE3093S (Communication and Network Engineering)
Tutorial 1
Date: 28 July 2023
Due Date (on Amathuba): 11 pm on 4 August 2023
INSTRUCTION: ANSWER ALL QUESTIONS.
1. List six access technologies. Classify each one as home access, enterprise access, or wide area
wireless access. (6 marks)
Home Access
Enterprise access
Wide-area wireless access
2. List two wide-area wireless access network available in Cape Town. For each type of access,
state the service provider, and the advertised data rate. (4 marks)
Wide-area wireless access Service provider
Data rate
3. Suppose Host A wants to send a large file to Host B. The path from Host A to Host B has three
links of rates R1=3 Mbps, R2=2 Mbps, and R3=1 Mbps.
(a) Assuming no other traffic in the network, what is the throughput for the file transfer? (2
marks)
(b) Suppose the file is 4 million bytes. Dividing the file size by the throughput, roughly how
long will it take to transfer the file to Host B? (2 marks)
4. What are the five layers in the Internet protocol stack? State one principal responsibility of
each of these layers? (5 marks)
5. Suppose Alice and Bob are sending packets to each other over a computer network. Suppose
Trudy positions herself in the network so that she can capture all the packets sent by Alice and
send whatever she wants to Bob; she can also capture all the packets sent by Bob and send
whatever she wants to Alice. List two malicious things Trudy can do from this position. (4
marks)
6. Suppose two hosts, A and B, are separated by 2,000 kilometers and are connected by a direct
link of 20 Mbps. Suppose the propagation speed over the link is 2.5 x 108 meters/sec.
(a) Calculate the bandwidth-delay product, R. dprop. (2 marks)
(b) Consider sending a file of 800,000 bits from Host A to Host B. Suppose the file is sent
continuously as one large message. What is the maximum number of bits that will be in the
link at any given time? (2 marks)
(c) Provide an interpretation of the bandwidth-delay product. (2 marks)
(d) What is the width (in meters) of a bit in the link? (2 marks)
7. (a) What advantage does a circuit-switched network have over a packet switched network (2
marks)?
(b) How long does it take to send a file of 256,000 bits from host A to host B over a single link
of a circuit-switched network? Assume that:
UNIVERSITY OF CAPE TOWN
Department of Electrical Engineering
EEE3093S (Communication and Network Engineering)
Tutorial 1
Date: 28 July 2023
Due Date (on Amathuba): 11 pm on 4 August 2023
(i) the time to establish an end-to-end circuit is 0.200 sec,
(ii) the link uses TDM with 16 slots, and
(iii) a host gets two slots per frame for data transmission. (2 marks)
8.
𝐿
According to the equation 𝑑𝑒𝑛𝑑−𝑡𝑜𝑒𝑛𝑑 = 𝑁 ∗ , the transmission delay of sending one packet
𝑅
across N links, where L is the packet length and R is the transmission rate. Assuming the
transmission rate to be constant at R, what will be the transmission delay for sending P packets
each of length L across:
(a)
(b)
(c)
1 link? (1 marks)
2 links? (2 marks)
N links? (2 marks)