RFC 516 (rfc516) - Page 2 of 2

Lost message detection

RFC 516                  LOST MESSAGE DETECTION                 May 1973


        hosts is set to zero.

        Each time a message is sent the current send message number is
        entered into a field in the message header, and the current send
        message number is incremented (modulo N, say N=256)

        Each time a message is received the message number from the
        message is compared to the current receive message number and:

            if the received message is the expected one then the message
            is acceptable and current receive message number is
            incremented (modulo N);

            if the received message is not the expected one then a
            message has been lost.

    What to do when a missing message is detected, not clear, but at
    least can be logged and reported to the network control center.  A
    missing message may not be fatal to an interactive conversation, but
    it is critical in a file transfer, thus I suggest that missing
    messages which are not recovered be cause to close the conversation.

The third scheme:

    Host to host acknowledgements could be required.  Such an
    acknowledgement scheme could be implemented similarly to the IMP to
    IMP scheme.  This is a serious change to the current protocols so I
    will not elaborate on it here, feeling that deeper study will be
    necessary to fully specify a reasonable host to host acknowledgement
    strategy.


Of these three suggestions the first is the most immediately practical
and implementable;  in fact several hosts all ready do this.  These
schemes also are non-conflicting, they could be implemented and used
simultaneously.








       [ This RFC was put into machine readable form for entry ]
       [ into the online RFC archives by Alex McKenzie with    ]
       [ support from GTE, formerly BBN Corp.             9/99 ]




Postel