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Unformatted text preview: 3.2.2 char char char char kludge kludge BSD/386 char char char char linemode linemode 4.4BSD char char char char linemode linemode Figure 26.11 Default modes of operation between various Telnet clients and servers.
The only two implementations in this figure that support real linemode are BSD/386 and
4.4BSD. These two servers are also the only ones that attempt to negotiate kludge line
mode if real linemode isn't supported by the client. All the clients and servers shown in this
figure do support kludge line mode, but they don't select it by default, unless negotiated by
Telnet defines its synch signal as the Data Mark command (DM in Figure 26.8) sent as
TCP urgent data. The DM command is the synchronization mark in the data stream that
tells the receiver to return to normal processing. It can be sent in either direction across a file:///D|/Documents%20and%20Settings/bigini/Docum...ti/homenet2run/tcpip/tcp-ip-illustrated/telnet.htm (18 of 26) [12/09/2001 14.47.45] Chapter 26. Telnet and Rlogin: Remote Login Telnet connection.
When one end receives notification that the other end has entered urgent mode, it starts
reading the data stream, discarding all data other than Telnet commands. The final byte of
urgent data is the DM byte. The reason for using TCP's urgent mode is to allow the Telnet
commands to be sent across the connection, even if the TCP data flow has been stopped by
TCP's flow control. We'll see examples of Telnet's synch signal in the next section.
As with the Rlogin client, the Telnet client also lets us talk to it, instead of sending what we
type to the server. The normal client escape character is Control-] (control and the right
bracket, commonly printed as "^]"). This causes the client to print its prompt, normally
"telnet> ". There are lots of commands that we can type at this point to change
characteristics of the session or to print information. A help command is provided by
most Unix clients that displays the av...
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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