RFC 2840 (rfc2840) - Page 5 of 12

TELNET KERMIT OPTION

RFC 2840                  TELNET KERMIT OPTION                  May 2000


      are restricted to ASCII C0 control characters other than Carriage
      Return and NUL.  The normal value is 1 (ASCII SOH).  The two
      Kermit partners normally use the same SOP, but may use distinct
      ones if desired.

   IAC SB KERMIT SOP is necessary to allow each Telnet partner to
   recognize subsequent incoming Kermit packets.  Data following the SOP
   is processed by the Kermit packet analyzer.  All other Kermit
   protocol parameters are automatically negotiated within the Kermit
   protocol upon the initial exchange of Kermit packets [KER].

   START-SERVER and STOP-SERVER commands must be sent by the WILL side
   whenever the state of the Kermit server changes.  When WILL is
   successfully negotiated the state of the WILL side is assumed to be
   STOP-SERVER.  If the server is active, the WILL side must send a
   START-SERVER to indicate the change in state.

   The receiver of a REQ-START-SERVER or REQ-STOP-SERVER is not required
   to agree to the request to change state.  The receiver must respond
   with either RESP-START-SERVER or RESP-STOP-SERVER to indicate the
   state of the Kermit Server subsequent to the request.  RESP-xxx-
   SERVER is sent instead of xxx-SERVER to enable the sender of REQ-
   xxx-SERVER to distinguish between the WILL side's spontaneous change
   in state and the response to the DO side's request.

   If the Kermit server receives a Kermit packet commanding it to cease
   Kermit service (such as a FINISH, REMOTE EXIT or BYE packet [KER]),
   it must send IAC SB KERMIT STOP-SERVER if the command is accepted.

   These rules ensure that the Telnet client's user interface always
   knows whether (and on which end) a Kermit server is available, and
   can therefore present the user only with valid choices, and that
   changes in state of one Telnet partner automatically switch the other
   to a complementary and valid state.

   While it is possible for a traditional telnet service (port 23) to
   implement this option while at the same time supporting the existing
   remote shell access functionality, it is not expected that this
   option will be used in that manner.  Instead, this option is
   primarily meant for use with dedicated Kermit services such as the
   Internet Kermit Service (port 1649) [IKS].

5. KERMIT PROTOCOL IMPLICATIONS

   The Kermit protocol is described elsewhere [KER].  It is an
   extensible and self-configuring protocol, like Telnet, and thus any
   two proper Kermit implementations should interoperate automatically.




Altman & da Cruz             Informational