Final by panniuniu


									              King Fahd University of Petroleum & Minerals

                      Electrical Engineering Department

                      EE400: Telecommunication Networks

                                  Final Exam

                      Instructor: Dr. M. A. Al-Andalousi

Date: June 5th, 2005
Duration: 7:30-9:30am (total 2hours)

                Student Name
                Student ID #

Note: Solve all 4 problems below. Do your best and show all your work. Final answers
without full details are not acceptable. You may want to use short computer programs for
some questions (in that case, include a listing of your program).

                   Problem #1 [10pts]
                   Problem #2 [10pts]
                   Problem #3 [10pts]
                   Problem #4 [10pts]
                   Exam Total [40pts]

Problem 1: [10pts]

   a) Give two advantages for using communication networks

   b) List one function for each of the following: Physical Layer and Link Layer

   c) Give two differences between Ethernet and T1/E1 transmission systems.

   d) What is a routing metric in packet switching networks? Give one possible choice.

   e) Explain two main characteristics of SONET/SDH
Problem 2: [10pts]
   Consider data transmission over a cellular wireless link with rate R=10 kbps.
   a) If we want to use this link as an access channel for setting up calls, explain why a
      MAC layer of the ALOHA type is suitable in this case?
   b) Let the access frame size be 100 bits. If the channel is fully loaded, find the
      maximum channel capacity (in frames/sec)?
   c) Assuming we use ALOHA, what is the number of frames that can successfully go
      through the channel (i.e, the throughput) in frames/sec?
      Note: the normalized throughput for ALOHA is given by S = G exp(-G), where G
      is the normalized frame arrival load (frame arrivals per frame transmission time).
      You need to find the maximum for S, and then use part ( b).
Problem 3: [10pts]

   Consider the following network:

                                2                           1
                            1                   3
                                    5           2
                                1                               2

   a) Use the Bellman-Ford (Distance Vector) algorithm to find the set of shortest paths
      from all nodes to destination Node 5
   b) Suppose that the link between Nodes 5 & 6 fails. Redo the Distance Vector
      algorithm to find the new routing table and associated costs
   c) Use the Dijkstra (Link State) algorithm to find the set of shortest paths from Node
      1 to all other nodes, and give the resulting routing diagrams as seen from Node 1.
Problem 4 [10pts]:
Consider a circuit switch serving 100 telephone subscribers. Assume the subscribers'
calling patterns are as follows:
     • 20% of them make 1 call/hour with duration 6 min/call
     • 40% make 9 calls/hour with duration 30 seconds/call
     • the rest make 6 calls/hour with duration 1 min/call

   a) Find the total offered traffic load a to the switch (measured in Erlangs)
   b) Assume you want to design the switch to guarantee at most 1% blocking
       probability. What should be the number of switch trunks to satisfy this?
   c) Suppose the subscriber number is doubled (i.e., 200), while still having the same
       calling pattern. Do you think the number of trunks needed to satisfy the 1%
       blocking must be exactly doubled? less than doubled?, or more than doubled
       compared to part b). Just give an intuitive answer, without computation.
Note: use the attached Erlang-B figure for your answers.


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