Supervisions

# Computer Networking

This is the set of exercises for my supervisions in Computer Networking, provided with the help of Malcolm Scott. It is a complementary set to the exercises handed out here: Supervision Handouts. Before each supervision, I will email you a list with which exercises you should attempt.

### Submitting work

You are expected to attempt to produce solutions to all the relevant questions before each supervision. I prefer submissions by email (PDF or text format). Please submit your work 24 hours before the supervision. However, if you want to submit a paper copy, please make sure to hand it in, to the Student Administration, 48 hours before the supervision. Please also email me, so that I know I have to pick up your submission.

 Contents

## Supervision 1

1. What is th OSI model used for?
2. For the lower four layers of the OSI model, give for each:
• a brief description of the layer;
• an example from the Internet;
• where it's implemented in the Internet in interconnection equipment and end systems.
3. Where would each of the following systems fit into the OSI model?
• a HTTP/HTTPS proxy server;
• a VPN (i.e. encapsulating encrypted IP packets inside another protocol);
• RFC 1149.
4. Calculate the total time required to transfer a 1000-KB file in the following cases, assuming an RTT of 50 ms, a packet size of 1 KB data, and an initial 2 × RTT of “handshaking” before data is sent:
• The bandwidth is 1.5 Mbps, and data packets can be sent continuously.
• The bandwidth is 1.5 Mbps, but after we finish sending each data packet we must wait one RTT before sending the next.
• The bandwidth is “infinite,” meaning that we take transmit time to be zero, and up to 20 packets can be sent per RTT.
• The bandwidth is infinite, and during the first RTT we can send one packet (21−1), during the second RTT we can send two packets (22−1), during the third we can send four (23−1), and so on.

From Computer Networks: A Systems Approach, 5th ed, question 3 from chapter 1

## Supervision 2

1. Please attempt to solve exercises 4(f), 5(b), 7, 8(b), 10, 11 from the Supervision Handouts.

## Supervision 3

1. Please attempt to solve exercises 14(c), 15, 16(a) from the Supervision Handouts.

## Supervision 4

1. Please attempt to solve exercises 18, 19(c), 20(a) from the Supervision Handouts.
• © 2014 Computer Laboratory, University of Cambridge
Information provided by Ionel Gog