26.1 | Identify all the delayed ACKs in Figure 26.5. |
A: | We expect segments 2, 4, and 9 from the server to be delayed. The time difference between segments 2 and 4 is 190.7 ms and the time difference between segments 2 and 9 is 400.7 ms. |
26.2 | Why was segment 12 in Figure 26.7 sent? |
A: | If one end of a connection is in TCP's urgent mode, then every time a segment is received, one is sent. This segment does not tell the receiver anything new (it is not acknowledging new data, for example), and it contains no data, it just reiterates that urgent mode has been entered. |
26.3 | We said that the Rlogin client must use a reserved port (Section 1.9). (Normally the Rlogin client only uses reserved ports in the range 512-1023.) What limitation does this present to a host? Is there a way around this? |
A: | There are only 512 of these reserved ports (512-1023), limiting a host to 512 Rlogin clients . The limit is normally less than 512 in real life, since some of the port numbers in this range are used as well-known ports by various servers, such as the Rlogin server. |