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(COMP362)2004_f_midterm.pdf
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HONG KONG UNIVERSITY OF SCIENCE & TECHNOLOGY
COMP362: Computer Communication Networks II
Fall Semester, 2004
Mid-term Examination
October 25, 2004 7:00 pm C 8:30 pm
Name: __________________ Student Number: ______________
Email: __________________ Lab Section Number: ___________
Instructions:
1.
This examination paper consists of 7 pages and 6 questions.
2.
Please write your name, student ID and Email on this page.
3.
For each subsequent page, please write your student ID at the top of the page in the space provided.
4.
Please answer all the questions within the space provided on the examination paper. You may use the back of the pages for your rough work and afterwards drawn a diagonal line through it to show that it is not part of your answer.
5.
Please read each question very carefully and answer the question clearly and to the point. Make sure that your answers are neatly written, readable and legible.
6.
Leave all pages stapled together.
7.
The examination period will last for 1 hour and 30 minutes.
8.
Stop writing immediately when the time is up.
Questions Marks Scores
1 15
2 6
3 15
4 14
5 10
6 10
Total 70
Question 1 (15 marks) Consider the two basic approaches identified for achieving broadcast: unicast emulation and network-layer (i.e., router-assisted) broadcast, and suppose spanning-tree broadcast is used to achieve network-layer broadcast. Consider a single sender and 32 receivers. Suppose the sender is connected to the receivers by a binary tree of routers (the receivers are at leaf nodes of the tree). What is the cost of sending a broadcast packet, in the cases of unicast emulation and network-layer broadcast, for this topology? Here, each time a packet (or copy of a packet) is sent over a single link, it incurs a unit of cost. What topology for interconnecting the sender, receivers, and routers will bring the cost of unicast emulation and true network-layer broadcast as far apart as possible? You can choose as many routers as youd like.
Question 2 (6 marks)
Consider the single-sender CDMA example in the following figure. What would
be the senders output (for the 2 data bits shown) if the senders CDMA code
were (1,-1,1,-1,1,-1,1,-1)?
Question 3 (15 marks) Consider the chaining example discussed at the end of the section Handoffs in GSM in the course. Suppose a mobile user visits foreign networks A, B and C, and that a correspondent begins a connection to the mobile user when it is resident in foreign network A. List the sequence of messages between foreign agents, and between foreign agents and the home agent as the mobile user moves from network A to network B to network C. Next, suppose chaining is not performed, and the correspondent (as well as the home agent) must be explicitly notified of the changes in the mobile users care-of-address. List the sequence of messages that would need to be exchanged in these sec