Subject: HPR Control Vectors

From: "Marcia Peters (8-444-4380)" <[email-masked]>
Date: Mon, 4 Dec 95 12:09:39 EST

Jim,

I don't blame you for being confused.  I'll try to shed some light on the
encodings IBM used for the HPR control vectors.

RTP first came to life as part of IBM's Networking Broadband Services
(NBBS) architecture.  We did the NBBS encodings using a different
codepoint space than SNA--they start at x'00'--since we presumed that a
format's use would be very clear in context.

Later, we created HPR by borrowing pieces of NBBS and grafting them onto
APPN.  A desire to preserve commonality between HPR and NBBS led us to
continue using RTP's NBBS encodings, including codepoints, padding to
force the alignment of fields after variable-length structures on 4-octet
boundaries, and specifying lengths as octets/4.

Therefore trace formatters need to interpret the RTP encodings in the
context of RTP.  RTP CVs 0-7 are parsed "KL" (key in the first byte)
while CVs 8 and up are parsed "LT" (length in byte 1, type/key in byte 2)
like the other APPN formats.  And HPR CVs x'80' and up are
context-sensitive.

In hindsight I admit that we were short-sighted.  Obviously this presents
difficulty not only for trace formatters but 7it will also require new
chapter(s) in the SNA Formats book.

Marcia Peters

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From: "jim (j.) cobban" <[email-masked]>
Date: Tue, 5 Dec 1995 11:55:00 -0500

>format's use would be very clear in context.

However the very definition of the CVIDs below X'80' is that they are NOT
context sensitive.

>chapter(s) in the SNA Formats book.

MOVED:  That new vector identifiers, which do not conflict with those already
	assigned to SNA CVs be assigned to these vectors.  A bit is added to
	the CV 61 to indicate whether the existing CVIDs or the
	non-context sensitive CVIDs are understood.  If this bit is set in an
	received XID, then the new CVID values are sent to that station.
	The Common Fields chapter of the SNA Formats document indexes the
	vectors under the non-conflicting identifiers, with a note referring
	to the obsolete context sensitive values.