RFC312

Network Working Group A. McKenzie RFC #312 BBN NIC 9342 22 March 1972 Categories: B.1

            Proposed Change in IMP-to-Host Protocol

    We are currently considering a redefinition of the IMP-to-Host

error message types (type 1 and type 8) and the creation of addi- tional IMP-to-Host error message types. We believe that these changes will assist the Hosts in determining appropriate recovery action, without causing any serious reprogramming problems. Our current plans are to install these changes within a few months; therefore we should be informed of any strong negative reactions relatively quickly.

    The proposed changes fall into two general classes as de-

scribed below:

    A)  General Error Message
        ---------------------

        Under certain circumstances, particularly when the Host
        has been unresponsive to queued input for a "long time"
        the IMP drops its ready line for a short period, causing
        the "error flip-flops" to be set (see RFC #270, NIC 7818).
        Under these conditions the IMP sends a few NOP's to the
        Host and then resumes normal operation.  We propose to
        send the Host a new message (message type 13) in addition
        to the NOPs; this message will tell the Host that the
        IMP's Ready Line was dropped, that the IMP's error flop
        was set, and that the IMP will respond to the next com-
        pletion of a Host-to-IMP message with a type 1 or type 8
        message (because of the setting of the IMP's error flop.

    B)  Error Messages which are Responses to Specific
        ----------------------------------------------
        Host-to-IMP Transmissions:
        --------------------------

        1)  IMP-to-Host message type 1 will be redefined to mean:
            "IMP's Error flip-flop was set on a message which
            the IMP cannot identify."

        2)  IMP-to-Host message type 8 will be redefined to mean:
            "IMP's Error flip-flop was set during receipt of the
            message identified by the 'source' and 'link number'
            bits of this error message."

        3)  IMP-to-Host message type 10 will be defined to mean:
            "A Host-to-IMP message was too short (and cannot be
            identified)."

        4)  IMP-to-Host message type 11 will be defined to mean:
            "A Host-to-IMP message was too long; the message is
            identified by the 'source' and 'link number' bits
            of this error message."

        5)  IMP-to-Host message type 12 will be defined to mean:
            "A Host-to-IMP message with an illegal message type
            code was received; the message is identified by the
            'source' and 'link number' bits of this error message.
            (Note that the erroneous type code is not included in
            the error message.)"

AAM/jm

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   [ direction of Alex McKenzie.                   12/96   ]