Subject: Question raised during discussion on 2-stage pacing

From: "Tom Moore ((919) 254-9932)" <[email-masked]>
Date: Wed, 2 Mar 94 09:59:52 EST

The following response from Gary Dudley (our ISR architect) addresses
the questions raised during the discussion on two-stage pacing..

  Tom
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During the discussion of APPN ISR handling of two-stage pacing at
the February AIW, it was stated that LUs is some LEN implementations
do not understand the ASPI bit in BIND and return in RSP(BIND) the
value received in BIND.  To accommodate such implementations, when a
RSP(BIND) is received with the ASPI set to 1 and any of the four pacing
window sizes not set to 0, the architecture specifies that fixed pacing
is used for the secondary stage.

A member of the audience asked if there were any cases in which no
pacing (rather than fixed pacing) would be used for the secondary stage.
The short answer to this question is yes because such LEN implementations
are detected when some window sizes are set to 0 and others are set to
nonzero values.

Consider, for example, the case where the RSP(BIND) specifies one-stage
pacing for both directions, the secondary receive and primary send window
sizes are set to 0, but the secondary send and primary receive window
sizes are set to a nonzero value.  In this case no pacing is used in the
primary-to-secondary direction, but fixed pacing is used in the
secondary-to-primary direction.  Likewise, when the secondary send and
primary receive window sizes are set to 0, but the secondary receive and
primary send window sizes are set to a nonzero value, fixed pacing is
used in the primary-to-secondary direction and no pacing is used in the
secondary-to-primary direction.  In this latter case the RSP(BIND) is
rejected if the receiving node does not support a receive pacing type of
none.  A similar analysis is possible when two-stage pacing is specified
in RSP(BIND) for either direction.

Gary Dudley                     [email-masked]   (919)254-4358
APPN Architecture
IBM Networking Hardware Division