Exercises

Exercises

21.1

In Figure 21.5 the first timeout was calculated as 6 seconds and the next as 24 seconds. If the ACK for the initial SYN had not arrived after the 24-second timeout expired , when would the next timeout occur?

21.2

In the discussion following Figure 21.5 we said that the timeout intervals are calculated as 6, 24, and then 48 seconds, as we saw in Figure 4.5. But if we watch a TCP connection to a nonexistent host from an SVR4 system, the timeout intervals are 6, 12, 24, and 48 seconds. What's going on?

21.3

Compare the performance of TCP's sliding window versus TFTP's stop-and-wait protocol as follows . In this chapter we transferred 32768 bytes in about 35 seconds (Figure 21.6) across a link with an RTT that averaged around 1.5 seconds (Figure 21.4). Calculate how long TFTP would take for the same transfer.

21.4

In Section 21.7 we said that the receipt of a duplicate ACK is caused by a segment being lost or reordered. In Section 21.5 we saw the generation of duplicate ACKs caused by a lost segment. Draw a picture showing that a reordering of segments also generates duplicate ACKs.

21.5

There is a noticeable blip in Figure 21.6 between times 28.8 and 29.8. Is this a retransmission?

21.6

In Section 21.6 we said that the 4.3BSD Tahoe release only performed slow start if the destination was on a different network. How do you think "different network" was determined? (Hint: Look at Appendix E.)

21.7

In Section 20.2 we said that TCP normally ACKs every other segment. But in Figure 21.2 we see the receiver ACK every segment. Why?

21.8

Are per-route metrics really useful, given the prevalence of default routes?



TCP.IP Illustrated, Volume 1. The Protocols
TCP/IP Illustrated, Vol. 1: The Protocols (Addison-Wesley Professional Computing Series)
ISBN: 0201633469
EAN: 2147483647
Year: 1993
Pages: 378

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