RFC 1090 (rfc1090) - Page 2 of 4

SMTP on X

RFC 1090                      SMTP on X.25                 February 1989


   encouraged, and may be up to 2048 bytes in total length.

   It is recommended that SMTP commands and responses be sent as single
   packets, or single more-data sequences, if only to facilitate
   debugging the protocol.  This is not a requirement.

5. Qualified data

   Packets with the Q bit set and interrupt packets are not used, and
   should be ignored if received.

6. Circuit resets

   If a level 3 circuit reset is received, the VC should be cleared, and
   the SMTP connection attempted again.  The retry may be after some
   delay, and may be with different call facilities.

7. Call facilities

   Any negotiable features selected by the X.25 call request facilities
   field may be used.  Implementations should provide the ability to
   specify facilities for each called address.

8. Character code

   The character code used on X.25 is the full ASCII-8 code, with no
   escapes or modifications.  Lines are terminated by CRLF (13 10
   decimal).  Implementations should, if possible, recognize lines
   terminated only by LF (10 decimal).

9. Closing the connection

   Unlike TCP, X.25 does not provide for synchronous delivery of data in
   transit when a clear request is in progress; any packets in transit
   are discarded when the VC is cleared.  Therefore, on X.25, the SMTP
   session layer is closed by the calling side when the Service Closing
   message is received, either in response to a QUIT command, or because
   the service must shut down.

10. Timeouts

   SMTP does not normally provide for timing out a session.  On X.25,
   the following has proven to be effective:

      10.1. call request

         If a call accept is not received within 100 seconds, or the
         Service Ready message is not received within (another) 120



Ullmann