RFC 690 (rfc690) - Page 2 of 3

Comments on the proposed Host/IMP Protocol changes

RFC 690    Comments on the proposed Host/IMP Protocol Change   June 1975


facilities will be available in the near term.

    This sounds like a good extension.

5. Source Host Control of Packets per Message.  The possibility will
exist for the source host to specify a message stream which will use a
given number of packets per multi-packet message (e.g. two packets per
message or five packets per message).  Since the IMP network will not
have to use eight packet-buffers for reassembly purposes, as at present,
this may result in better services for such messages.  This will help
users who need both low delay and high throughput.

    This seems strange, why not use the message length (as provided in 3
    above) to determine the number of packets needed for this message.

6. Unordered (type-3) Message Change.  Unordered messages will be
indicated by a handling type rather than by a message type as at
present.  This is compatible with the need to check the host access
control capabilities of all messages.  This will provide a slight
backward incompatibility for the three or so hosts which presently use
type-3 messages in their research.

    Good, a current special case becomes a general facility.

7. Change in Format of Fake Host Addresses.  The For/From IMP bit will
be eliminated.  The fake host addresses will be the four highest host
numbers (e.g. IMP Teletype will be host 252).

    Another change for the better.

8. Addition of a Parameter to the IMP to Host NOP.  The IMP to host NOP
will have added to it a parameter specifying the address (IMP and host
number) of the host.

    Ah, a clever touch, very handy.

9. Backward Compatibility.  The old and new formats will be supported in
parallel in the IMPs for the foreseeable future to allow gradual
phaseover of host software.   A host will be able to specify to its IMP
whether the old or new formats are to be used; thus, it will be possible
for the host to specify switching back and forth between the two modes
for debugging purposes.  The specification of the mode to be used will
be possible via a proper choice of format in the host to IMP NOP
message;  The IMP will use the mode of the Host to IMP NOP message the
IMP has received.  Further, a host may select to use either the old or
new format without needing to know more about the other format message
than to discard them should they arrive.  The IMP will initialize by
sending several NOP messages of each type to give the hosts its choice.



Postel