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Unformatted text preview: the ACKs from the client to the server appear to be delayed: segments 6, II, 13, 15,
17, and 19. The time differences of the last five from segment 6 are 400.0, 600.0, 800.0,
1000.0, and 2.600 ms.
26.2 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 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 file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/append_d.htm (17 of 20) [12/09/2001 14.48.04] Appendix D: Solutions to Selected Exercises this range are used as well-known ports by various servers, such as the Rlogin server.
TCP's limitation is that the socket pair defining a connection (the 4-tuple) must be
unique. Since the Rlogin server always uses the same well-known port (513) multiple
Rlogin clients on a given host can use the same reserved port only if they're connected to
different server hosts. Rlogin clients, however, don't use this technique of trying to reuse
reserved ports. If this technique were used, the theoretical limit is a maximum of 512
Rlogin clients at any one time that are all connected to the same server host. Chapter 27
27.1 Theoretically the connection cannot be established while the socket pair is in the
2MSL wait on either end. Realistically, however, we saw in Section 18.6 that most
Berkeley-derived implementations do accept a new SYN for a connection in the
27.2 These lines are not part of a server reply that begins with a 3-digit reply code, so
they cannot be from the server. Chapter 28
28.1 A domain literal is a dotted-decimal IP address within square brackets. For example:
28.2 Six round trips: the HELO command, MAIL, RCPT, DATA, body of the message,...
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