Comments on the proposed Host/IMP Protocol changes (RFC0690)
Original Publication Date: 1975-Jun-06
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
This is a set of comments on Dave Walden's RFC 687 suggesting a set of changes to the host--imp protocol. Dave's points are reproduced here with my comments underneath.
Network Working Group Jon Postel
RFC # 690 USC-ISI
NIC # 32699 June 6, 1975
Comments on the proposed Host/IMP Protocol Change
This is a set of comments on Dave Walden's RFC 687 suggesting a set of
changes to the host--imp protocol. Dave's points are reproduced here
with my comments underneath.
1. Expanded Leader Size. The leader will be expanded from two to five
16-bit words. This will provide space for necessary field expansions
The existing protocols set the host header at 40 bits so that taken
together with the leader the length was 72 bits; a nice boundary for
both 8 bit and 36 bit machines. This suggestion would result in a
prefix of 80 + 40 = 120 bits, not so nice (unless the host header is
extended to 64 bits for a total prefix of 144 bits).
2. Expanded Address Field. The address field will be expanded to 24
bit, 16 bits of IMP address and 8 bits of host address. This expansion
is more than adequate for any foreseeable ARPA Network growth.
Just a few years ago 256 seemed like a lot of hosts, perhaps, a
extensible scheme might be more appropriate. (I concede 16,777,216,
3. New Message Length Field. A new field will be added which will allow
the source host to optionally specify the message length (in bits) to
the IMP subnetwork. The IMP subnetwork may be able to use this
information (when available) to better utilize network buffer storage.
The destination host may also be able to use this information to better
utilize its buffer storage. This field will be 13 bits wide.
This sound very useful, but if we every want to have longer messages
than now the field should be wider, say 16 bits.
4. Expanded Handling Type Field. The handling type field which now is
used to distinguish between priority and non-priority message streams,
etc., will be expanded to eight bits. This expanded field will provide
for the possibility of a number of parallel message streams having
different handling characteristics between pairs of hosts; e.g.,
priority, non-priority, varying numbers of packets per message (see
below), unordered messages (i.e. the present type-3 messages), a message
stream requiring guaranteed capacity, etc, Note that only some of these
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 d...