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Unformatted text preview: ; vangogh.7777: . ack 15 win 4096
bsdi.8888 > vangogh.7777: F 14:14(0) ack 15
vangogh.7777 > bsdi.8888: . ack 15 win 8192 Figure 18.18 Exchange of segments during simultaneous open. 18.9 Simultaneous Close
We said earlier that one side (often, but not always, the client) performs the active close,
causing the first FIN to be sent. It's also possible for both sides to perform an active close, and
the TCP protocol allows for this simultaneous close.
In terms of Figure 18.12, both ends go from ESTABLISHED to FIN_WAIT_1 when the
application issues the close. This causes both FINs to be sent, and they probably pass each other
somewhere in the network. When the FIN is received, each end transitions from FIN_WAIT_1
to the CLOSING state, and each state sends its final ACK. When each end receives the final
ACK, the state changes to TIME_WAIT. Figure 18.19 summarizes these state changes. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_conn.htm (25 of 37) [12/09/2001 14.47.16] Chapter 18. TCP Connection Establishment and Termination Figure 18.19 Segments exchanged during simultaneous close.
With a simultaneous close the same number of segments are exchanged as in the normal close. 18.10 TCP Options
The TCP header can contain options (Figure 17.2). The only options defined in the original
TCP specification are the end of option list, no operation, and the maximum segment size
option. We have seen the MSS option in almost every SYN segment in our examples.
Newer RFCs, specifically RFC 1323 [Jacobson, Braden, and Borman 1992], define additional
TCP options, most of which are found only in the latest implementations. (We describe these
new options in Chapter 24.) Figure 18.20 shows the format of the current TCP options-those
from RFC 793 and RFC 1323. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_conn.htm (26 of 37) [12/09/2001 14.47.16] Chapter 18. TCP Connection Establishment and Terminat...
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- Spring '12