TCP IP Illustrated

Our sock program lets us specify a pause option p

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Unformatted text preview: only ACKs segments containing data. If an acknowledgment is lost, we could end up with both sides waiting for the other: the receiver waiting to receive data (since it provided the sender with a nonzero window) and the sender waiting to receive the window update allowing it to send. To prevent this form of deadlock from occurring the sender uses a persist timer that causes it to query the receiver periodically, to find out if the window has been increased. These segments from the sender are called window probes. In this chapter we'll examine window probes and the persist timer. We'll also examine the silly window syndrome, which is tied to the persist timer. 22.2 An Example To see the persist timer in action we'll start a receiver process that listens for a connection request from a client, accepts the connection request, and then goes to sleep for a long time before reading from the network. Our sock program lets us specify a pause option -P that sleeps between the server accepting the connection request and performing the first read. We'll invoke the server as: svr4 % sock -i -s -P100000 5555 This has the server sleep for 100,000 seconds (27.8 hours) before reading from the network. The client is run on the host bsdi and performs 1024-byte writes to port 5555 on the server. Figure 22.1 shows the tcpdump output. (We have removed the connection establishment from the output.) file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_pers.htm (1 of 11) [12/09/2001 14.47.29] Chapter 22. TCP Persist Timer 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 0.0 0.191961 ( 0.1920) 0.196950 ( 0.0050) 0.200340 ( 0.0034) 0.207506 ( 0.0072) 0.212676 ( 0.0052) 0.216113 ( 0.0034) 0.219997 ( 0.0039) 0.227882 ( 0.0079) 0.233012 ( 0.0051) 0.237014 ( 0.0040) 0.240961 ( 0.0039) 0.402143 ( 0.1612) 5.351561 ( 4.9494) 5.355571 ( 0.0040) 10.351714 ( 4.9961) 10.355670 ( 0.0040) 16.351881 ( 5.9962) 16.355849 ( 0.0040) bsdi.1027 > svr4.5555: P 1:1025(102...
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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.

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