TCP IP Illustrated

2 the rlogin client is blocked from writing to the

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Unformatted text preview: le to the terminal, and then stop the output by typing Control-S. When the output stops we type our interrupt key (DELETE) to abort the program: sun % rlogin bsdi all the operating system greetings bsdi % cat /usr/share/misc/termcap ^? bsdi % output big file to terminal lots of terminal output we type Control-S to stop the output, and wait until the output stops type our interrupt key, and this is echoed then our prompt is output The following points summarize the state of the client, the server, and the connection. 1. We stop the terminal output by typing Control-S. 2. The Rlogin client is blocked from writing to the terminal, since the terminal's output buffer will fill. 3. The Rlogin client therefore cannot read from the network, so the client's TCP receive buffer fills. 4. The client's TCP advertises a window of 0 to stop the sender (the Rlogin server's TCP) when the receive buffer fills. 5. The server's TCP send buffer fills when its output is stopped by the client's window of 0. 6. The Rlogin server is stopped, since the send buffer is full. Therefore, the Rlogin server cannot read from the application that's running on the server (cat). 7. The cat application stops when its output buffer fills. 8. We then type the interrupt key to terminate the cat application on the server. This is sent from the client TCP to the server TCP because this direction of data flow has not been flow-control stopped. 9. The cat application receives the interrupt, and terminates. This causes its output buffer (which the Rlogin server is reading) to be flushed, which wakes up the Rlogin server. The Rlogin server then enters urgent mode and sends the "flush output" command (0x02) to the client. Figure 26.6 is a summary of the data flow from the server to the client. (The sequence numbers are taken from the time line that we show next.) file:///D|/Documents%20and%20Settings/bigini/Docum...ti/homenet2run/tcpip/tcp-ip-illustrated/telnet.htm (10 of 26) [12/09/2001 14.47.45] Chapter...
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