rfc983


John Leong (leong@andrew.cmu.edu)
Thu, 12 Jun 86 12:51:14 EDT


Having been involved with the ISO Transport Protocol definition a few years
ago (started when it still an ECMA draft spec and a very very prelimary draft
ISO spec from the Tokyo or was it Berlin meeting), it was very interesting to
read the RFC983 "ISO Transport Services on Top of the TCP".

I am afraid the RFC is very much NOT in the spirite of things.

Every (newer) ISO protocol specification must be accompanied by a service specification.
The primitives defined in the service specification is intended solely for explaination
of the service offered by the protocol. Like the OSI reference model (from which
it is derived), it is not an implementation guide. Furthermore, the primitives
defines LOCAL INTERFACE and not PROTOCOL. Actually if you look at protocols
for every layer, (e.g. Session) the service primitives and terminology (straight
out of OSI) such as SAP's looks virtually identical.

The actual service implementation at the interface is very dependent on the
local operating system environment. Hence Connection Request, Connection Confirmation,
Connection Indication etc. are manifested differently in an UNIX 4.2 socket
environment from that of an VMS-VAX or whatever other operating system environment.

It is definitely not the intent to have the primivites encoded and transported
in a peer-to-peer fashion as a protocol. In that case, a service specification
have to be defined for this "new" protocol and we quickly get into a recursion-with-no-exit
situation!!!

In general, it is important for one to produce good generic protocol interface
design so that a particluar protocol implementation or even the protocol itself
can easily be replaced without affecting the code in the upper or lower layer.
A well designed generic interface can be used for every layer although the data
structure associated with a primitive will most likely to be different. The
UNIX 4.2 socket mechanism is a good start.

One final note, for people who is really interested in implementation of the
Transport and Session Protocols, the best set of documentation I have seen (besides
the offical specification) can be obtained from :

National Bureau of Standards, @*
Institute for Computer Sciences and Technology, @*
Center for Computer Systems Engineering, @*
Systems and NetworkArchitecture Division

The set is produced under contract by BBN back in 1980/81. It contains service
specification, protocol specification, as well as implementation guide including
wonderful pseudo codes. While the Transport Protocol spec is not 100% ISO spec,
it is 99% close.



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