Re: ISO8473 vs. IP

Paul Tsuchiya (
Tue, 8 Sep 87 14:02:13 EDT

> Comparison of DoD IP and ISO IP:
> As Paul pointed out, functionally the same. Here are some other differences:
> - No upper layer protocol ID in ISO8473...................
> The two biggest differences I see are the address part and lack of
> upper layer proto id.
> Rob Hagens
> UW Madison Computer Science

This is not to say that ISO8473 cannot distinguish between upper layer
protocols. The address in ISO8473 is used to do the distinguishing
(the address is called the Network Service Access Point Address, which
defines the boundary between the transport thing and the network thing.
I don't want to get into what "thing" is).

Practically speaking, one reserves a byte (sorry, octet) in the NSAP
address, usually called the NSAP selector, to do the job of the
protocol id field in DoD IP. Boils down to the same thing as far as
I can tell.

(I'm wondering if it is kosher to use the NSAP selector byte to
distinguish between different transport classes (TP0, TP1, ...., TP4).
Something tells me it isn't, but I don't see how someone could stop you.
I'll have to bring that up at the next 3.3 meeting).

        Paul Tsuchiya
        The MITRE Corp.

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