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Network Working Group K. Victor Request for Comments: 576 September 1973

                   Proposal for Modifying Linking

 We plan to modify the link jsys in TENEX to work in a little bit
 better way in terms of the user interface.  Conversations with BBN
 indicate that they have no complaints with the current
 implementation.  However, if after we have gained experience with our
 new implementation, we will let them know about it and they will
 review the new implementation and possibly accept it as part of
 standard TENEX.

 I would appreciate feedback in the next couple of days so that I can
 go ahead and implement this proposal (or a modified proposal or
 nothing...).  (I estimate that it will only take a couple of hours to
 implement!)

 (Note that by modifying the jsys, the proposed changes as specified
 will be in effect at the user level in the exec.)

 The default state for all users will remain as it currently is, i.e.
 RECEIVE LINKS.

 Now, consider users A, B, and C.

 If A and B link to each other they are now holding a conversation.

 After establishing a conversation, all members of the conversation
 will be placed in the REFUSE LINKS state.

 If user C (or any other user) now tries to link to user A (or B), the
 bell will ring on users A (or B) and C terminals indicating that A
 (or B) is in a REFUSE LINKS state.

    If A ignores the bell then C is not admitted to the conversation
    and A and B can continue their conversation as if C had never
    tried to enter the conversation.

    However, if A does a RECEIVE LINKS while the bell is ringing (the
    bell rings for approximately 15 seconds), then C will be linked
    into the conversation and not to just user A.  Thus A and B will
    be linked, A and C will be linked, and B and C will be linked,
    i.e., a three way conversation.  Also, users A, B, and C will be
    in the REFUSE LINKS state.

Victor [Page 1]  RFC 576 Proposal for modifying linking September 1973

 Whenever a user leaves a conversation, his state will be set
 automatically to RECEIVE LINKS.

    Thus, when user C does a break links the resulting states will be:

       A and B will be linked and both will be in REFUSE LINKS

       C will be out of the conversation and will be in RECEIVE LINKS

    Now, when A or B does a BREAK LINKS there will no longer be a
    conversation and both A and B will be in the RECEIVE LINKS state.

 To summarize:

    After any conversation is established, all members of the
    conversation are placed in the REFUSED LINKS state.

    When a user links to a terminal or a user, he is in fact linking
    into a conversation if one exists or to an individual if no
    conversation is taking place.

    When a user leaves a conversation, she is placed in the RECEIVE
    LINKS state.

 Changes to the TLINK jsys will be necessary to implement the above.
 No changes are required in the EXEC.  In addition to the above
 changes, we will add a new jsys that will return the link and advise
 status for a passed terminal, i.e., you will be able to tell which
 lines are linked to the passed terminal, which lines the passed
 terminal is linked to, which line the passed terminal is advising,
 and/or which line is advising the passed terminal.  This information
 will probably be incorporated into the systat printout, the where is
 printout, and will probably be used within NLS for shared screen
 work.

        [This RFC was put into machine readable form for entry]
           [into the online RFC archives by Bob German 7/99]

Victor [Page 2]