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Chapter 5:
The Link Layer: Links, Access Networks, and LANs

5.1 Suppose the information content of a packet is the bit pattern 1111 1011 1001 1100 and an even parity scheme is being used. What would the value of the field containing the parity bits be for the case of a two-dimensional parity scheme? Your answer should be such that a minimum-length checksum field is used.

5.2 Refer to the Cyclic Redundancy Check (CRC) codes discussed in the textbook and follow the conventions used in the textbook. Consider the 5-bit generator, G=10011, and suppose that D has the value 1010101010. What is the value of R? Show the process how you obtain the solution.

5.3 Consider two nodes A and B uses the slotted ALOHA protocol to contend for a channel. Suppose node pA and pB are A and B’s retransmission probabilities. Provide a formula for node A’s average throughput. What is the total efficiency of the protocol with these two nodes?

5.4 A disadvantage of the content of approach for LANs, such as CSMA/CD, is the capacity wasted due to multiple stations attempting to access the channel at the same time. Suppose that time is divided into discrete slots, with each of N stations attempting to transmit with probability p during each slot. What fraction of slots is wasted due to multiple simultaneous transmission attempts?

5.5 In CSMA/CD, after the 5th collision, what is the probability that a node chooses k=5? The result k=5 corresponds to a delay of how many seconds on a 10 Mbps Ethernet?