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? |