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Unformatted text preview: on of the connection. 22.4 Summary
TCP's persist timer is set by one end of a connection when it has data to send, but has
been stopped because the other end has advertised a zero-sized window. The sender
keeps probing the closed window using a retransmission interval similar to what we saw
in Chapter 21. This probing of the closed window continues indefinitely.
When we ran an example to see the persist timer we also encountered TCP's avoidance of
the silly window syndrome. This is to prevent TCP from advertising small windows or
from sending small segments. In our example we saw avoidance of the silly window
syndrome by both the sender and the receiver. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_pers.htm (10 of 11) [12/09/2001 14.47.29] Chapter 22. TCP Persist Timer Exercises
22.1 In Figure 22.3 notice the times of all the acknowledgments (segments 5, 7, 9, 11, 13,
15, and 17): 0.170, 5.170, 10.170, 15.170, 15.370, 20.170, and 25.170. Also notice the
time differences between receiving the data and sending the ACK: 164.5, 18.5, 18.7,
18.8, 198.3, 18.5, and 19.1 ms. Explain what's probably going on.
22.2 In Figure 22.3 at time 25.174 a window of 767 is advertised, but 768 bytes are
available in the receive buffer. Why the difference of 1 byte? file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_pers.htm (11 of 11) [12/09/2001 14.47.29] Chapter 23. TCP Keepalive Timer TCP Keepalive Timer
Many newcomers to TCP/IP are surprised to learn that no data whatsoever flows across
an idle TCP connection. That is, if neither process at the ends of a TCP connection is
sending data to the other, nothing is exchanged between the two TCP modules. There is
no polling, for example, as you might find with other networking protocols. This means
we can start a client process that establishes a TCP connection with a server, and walk
away for hours, days, weeks or months, and the connection remai...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12