Re: Notices to ASPTM message mapping

Kolomaznik,

Kolomaznik Jan wrote:                                           (Tue, 30 May 2006 09:08:23)
> Ad 1) I think, it will be better if any recommendation word (like
> SHOULD) will be used in talking about a possibility of ASPTM messages
> mapping on any SCTP stream carrying data traffic. I agree that in
> situations where more than one data traffic streams are used the
> minimization of possible packet loss cannot be so high, but in cases
> where only one data traffic stream is used it is 100%.

Yes, but there are other procedures for minimizing message loss and
missequencing.

See

  http://www.ietf.org/internet-drafts/draft-bidulock-sigtran-corid-03.txt

for example and particularly section 4.3 on interworking with an
implementation that does not support these enhanced procedures.

It is still possible, you see, to set a timer and send a BEAT and expect
a BEAT ACK on each data stream (or timer expiry) before sending ASPTM on
Stream 0.  These procedures can guarantee 100% that there is no message
loss as a result of ASPTM for multiple data streams.

Therefore, SHOULD is too strong, and MAY was chosen.

> 
> Ad 2) If ASTPM Ack messages will use a data traffic SCTP stream, I do
> not see any practical reason for this type of restriction. - But if
> ASPTM Ack messages will be transmitted on SCTP stream 0, there is a
> theoretical possibility that ASPTM message will be evaluated earlier
> than previously sent data message(s). This possibility could happen both
> in ASP Active and ASP Inactive procedures. So my meaning is, when a
> ASPTM not Ack message used data traffic SCTP stream, the ACK message
> should use data traffic SCTP stream also.

BEAT, BEAT-ACK servers the same purpose. This is why we permitted BEAT
to be sent on any stream.

> The second thing is that from protocol theory point of view the Ack on
> different stream than acknowledged message looks not good. So if there
> is not any practical reason for changing of stream for Ack message, the
> Ack message should use the same stream.

If the BEAT procedure is used, it is even better to send ASPTM on stream 0
because it can be delivered ahead of data traffic pertaining to other AS
on the data streams.  We don't use SHOULD to make an implementation do
something a certain way when other equally valid options exist and there are
not interoperability issues.  The protocol procedures exist for the BEAT
procedure and which method is chosen is a purely local matter.

--brian

-- 
Brian F. G. Bidulock
[email protected]
http://www.openss7.org/