RFC 1143 (rfc1143) - Page 2 of 10

The Q Method of Implementing TELNET Option Negotiation

RFC 1143                        Q Method                   February 1990


   writing a new TELNET implementation.

   NOTE: Reading This Document

      A TELNET implementation is not compliant with this RFC if it fails
      to satisfy all rules marked MUST.  It is compliant if it satisfies
      all rules marked MUST.  If it is compliant, it is unconditionally
      compliant if it also satisfies all rules marked SHOULD and
      conditionally compliant otherwise.  Rules marked MAY are optional.

      Options are in almost all cases negotiated separately for each
      side of the connection.  The option on one side is separate from
      the option on the other side. In this document, "the" option
      referred to by a DONT/WONT or DO/WILL is really two options,
      combined only for semantic convenience.  Each sentence could be
      split into two, one with the words before the slash and one with
      the words after the slash.

      An implementor should be able to determine whether or not an
      implementation complies with this RFC without reading any text
      marked DISCUSSION.  An implementor should be able to implement
      option negotiation machinery compliant with both this RFC and RFC
      854 using just the information in Section 7.

2. RFC 854 Option Negotiation Requirements

   As specified by RFC 854: A TELNET implementation MUST obey a refusal
   to enable an option; i.e., if it receives a DONT/WONT in response to
   a WILL/DO, it MUST NOT enable the option.

   DISCUSSION:

      Where RFC 854 implies that the other side may reject a request to
      enable an option, it means that you must accept such a rejection.

   It MUST therefore remember that it is negotiating a WILL/DO, and this
   negotiation state MUST be separate from the enabled state and from
   the disabled state.  During the negotiation state, any effects of
   having the option enabled MUST NOT be used.

   If it receives WONT/DONT and the option is enabled, it MUST respond
   DONT/WONT repectively and disable the option.  It MUST NOT initiate a
   DO/WILL negotiation for an already enabled option or a DONT/WONT
   negotiation for a disabled option.  It MUST NOT respond to receipt of
   such a negotiation.  It MUST respond to receipt of a negotiation that
   does propose to change the status quo.





Bernstein