Subject: SIGNATURE: Now and then...

From: Peter Johansson <[email-masked]>
Date: Wed, 3 Feb 1999 12:49:05 EST

After reviewing all of the discussion on the "signature" field in the link
encapsulation header, I suggest that we remove it and label the field
reserved.

Because P1394.1 is still work in progress, it is not yet clear that a node
will be able to query a bridge portal to obtain its own virtual node ID.
Without this capability, I think we will be at a loss to provide a "mostly
unique" number for datagram fragment identification. On the other hand, we
have assurances from P1394.1 that the source_ID (whther obtained from an
asynchronous packet header or a GASP header) will be end-to-end unique between
any pair of corresponding nodes, whther local or remote.

The reassembly algorithm should make it clear that the recipient SHALL use the
sender's source_ID to correlate datagram fragments from each node.

Now, on to a digression about "reserved" vs. "zeros". The definition of
RESERVED requires the recipient NOT check the field for any values. This
definition does permit future extensions, but lays a burden of responsibility
on the future standards: the behavior of the new formats (that make use of
previously reserved fields) must overlay, without any ill-effects, the
behavior of the previous formats. In other words, when a formerly reserved
field is defined it is necessary to define zero values as having exactly the
same effect as in the prior standard.

Hence I suggest that "signature" be classified reserved.

Regards,

Peter Johansson

Congruent Software, Inc.
98 Colorado Avenue
Berkeley, CA  94707

(510) 527-3926
(510) 527-3856 FAX

[email-masked]