RFC 559 (rfc559) - Page 1 of 5

Comments on The New Telnet Protocol and its Implementation

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Network Working Group                                 Abhay K. Bushan
Request For Comments #559                             MIT Project MAC
NIC # 18482                                           August 15, 1973



       Comments on the new TELNET Protocol and its Implementation


     We at MIT-DN have implemented the new TELNET protocol (both server
and user).  This RFC describes our experience with the implementation
(particularly the use of GO AHEAD) and in bringing the new User and
Server TELNET's in operation (the new TELNET is not compatible with the
old).  We have a few suggestions here which should help other
implementors and lead to a smoother transition to the new protocol.

I. OUR TELNET SERVER IMPLEMENTATION

     Our new server TELNET accepts both the "old" and the "new" TELNET
"control sequences".  Currently we have the ECHO and the "Suppress Go
Ahead" options implemented and do the "right thing" to varying degrees
with the Interrupt Process (IP), Erase Character (EC), Abort Output
(AO), Are You There (AYT), Break, and Synch character sequences.

 A. The ECHO Option

     The TELNET server comes up in the default local echo mode and
accepts both the old and the new TELNET control sequences.  The server
starts the negotiation for remote echo (server echoing) by sending the
sequence "IAC WILL ECHO" but changes the echo mode only when an
affirmative "IAC DO ECHO" is received.  After the cutoff date for old
protocol we will stop "honoring" the old TELNET control sequences.

 B. The Go Ahead and Suppress GA option

     The server comes up in the send GA mode and transmits the required
"IAC GA" sequence whenever the server detects that it needs to send a
GA.  It should be noted that our scheme for sending GA's works most but
not all of the time.

     There is really no reliable way for our server TELNET to find out
when a process is actually waiting for network input.  On our system,
the server TELNET does not "control" user's process, it only acts as a
terminal handler at the TTY level.







Bushan
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