Communication Protocol Engineering
Discussion 4 (due on April 22, 2015)
1. Please summarize the following mechanisms that together provide for reliable data
transfer:
 Checksum
 Timer
 Sequence Number
 Acknowledgment
 Negative Acknowledgment
 Window, Pipelining
2. Please compare the following two pipelined error recovery protocols:
 Go-Back-N (GBN)
 Selective Repeat (SR)
(What are the FSM description of the sender and receiver when applying these reliable
data transfer protocols?)
Use GBN or SR?
(1) If errors low
(2) If errors high
(3) If bandwidth cheap
(4) If bandwidth costly
(5) If memory costly at the receiver
(6) If memory cheap at the receiver
(7) Suppose the sender is a powerful server and the receiver is a small device (a watch or
a sensor node) with limited resources (low memory, slow MCU, etc.). Which
protocol will you use to send the data from the sender to the receiver? Why?
3. Consider the GBN and SR protocols. Suppose the sequence number space is of size k.
What is the largest allowable sender window that will avoid the occurrence of problems
such as that in Figure 3.27 for each of the protocols?
4. Is TCP’s error-recovery mechanism a GBN or an SR protocol?