CIS 677: Second Exam
 
Mo, May 11, 1997, 50 minutes
Open Notes, Open Books
Circle the right answer for each problem
Points per answer: correct 2, incorrect 0, none 1

• Problem #1 Bit stuffing calls for adding a 0 bit after each run 11111
  1. Between the end delimiters of the frame
  2. Just within the data field of the frame
  3. Throughout the whole frame
  4. None of the above
• Problem #2 For every string, even and odd parity error corrections
  1. Always agree on the bit they add
  2. Never agree on the bit they add
  3. Sometimes agree on the bit they add, and sometime disagree
  4. None of the above, because they change a bit-not add a bit.
• Problem #3 CRC-16 requires that the given binary string be divisible by
  1. A constant made out of of 16 bits
  2. A polynomial of degree 17
  3. The integer 16
  4. None of the above
• Problem #4
  1. The stop-and-wait protocol can't simulate the sliding-window protocol, and the sliding-window protocol can't simulate the stop-and-wait protocol
  2. The stop-and-wait protocol can simulate the sliding-window protocol, and the sliding-window protocol can simulate the stop-and-wait protocol
  3. The stop-and-wait protocol can't simulate the sliding-window protocol, but the sliding-window protocol can simulate the stop-and-wait protocol
  4. The stop-and-wait protocol can simulate the sliding-window protocol, but the sliding-window protocol can't simulate the stop-and-wait protocol
• Problem #5 Consider a communication between two stations using the stop-and-wait ARQ protocol. Assume that only the odd frames submitted by a sending station reach their destination, and that only the odd acknowledgments submitted by the receiver station reach their destination.

  That is, the first frame successfully reaches its destination, the second fails to do so, the third reaches successfully its destination, and so forth. Similarly, the first acknowledgment successfully reaches its destination, the second fails to do so, the third reaches successfully its destination, and so forth.

  The number of frames, plus the number of acknowledgments, submitted until the sender gets a second acknowledgment, equals

  1. 7
  2. 8
  3. 9
  4. None of the above
• Problem #6 A control field starting with 00, in a HDLC frame, identifies a frame of type
  1. Information
  2. Supervisory
  3. Unnumbered
  4. None of the above
• Problem #7 Consider the following circuit switch

  

  The number of possible connections at any given time is at most

  a. 3 b. 4 c. 5 d. 6

• Problem #8 Synchronous time-division multiplexing for circuit switching may be coupled with
  1. Adaptive routing but not alternate routing
  2. Alternate routing but not adaptive routing
  3. Alternate routing or adaptive routing
  4. Neither alternate routing nor adaptive routing
• Problem #9
  1. Circuit switching must determine the communication path in advance, but packet switching can't do so
  2. Circuit switching must determine the communication path in advance, and packet switching may do so too
  3. Circuit switching does not need to determine the communication path in advance, and neither does packet switching
  4. None of the above holds
• Problem #10 Assume a linear network consisting of two end stations and three packet switching nodes.

  If node A sends to node B 10 packets of size 550 bits each, and if the travel time for each packet over each link is 550 time units, then all the packet will reach B after

  1. 5500 time units
  2. 6050 time units
  3. 6600 time units
  4. 7150 time units
• Problem #11 Which of the following networks can not offer connectionless service
  1. Circuit switching networks
  2. Packet switching with virtual circuits
  3. Packet switching with datagrams
  4. Linear packet-switching networks (see figure in previous example).
• Problem #12 Consider the following packet switching network, with the possibility that some of the links are broken.

  What should be the least value assigned to the counter of a packet, by the flooding routing algorithm, when the packet is to be submitted across the above network.

  1. 3
  2. 4
  3. 5
  4. 6
• Problem #13 Consider the following packet switching network, and the information available to node `b' for computing its nest-destination table according to the first-generation adaptive routing algorithm of ARPANET.

  Which of the following cases provides the vector of next destinations for the targets (a,c,d,e,f).

  1. (a,c,f,c,f)
  2. (a,c,f,f,f)
  3. (c,c,f,c,f)
  4. none of the above