Subject: [Sigtran] M2PA MSU_ACK frequency issue

From: Javier Kim <[email-masked]>
Date: Wed, 17 Sep 2003 13:05:16 -0700 (PDT)

Hi All,

>From the recent Plugtest in Sophia Antipolis it was observed that some
M2PA implementations didn't send MSU_ACKs except by long timer trigger
(.5 second).  On a 3000 message-per-second link this could lead to
recovery queues of 1500 MSUs or more.  It was determined that more
frequent MSU_ACKs would be better and add little or no overhead for most
bi-directional message flows.

We suggest that the draft be amended to require an MSU or MSU_ACK be
returned no less frequently than every 8 MSUs received.  This would
keep the M2PA recovery queues shorter, and faster to process, in the event
of a change-over.

Best regards,

Javier Kim

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From: Tom George <[email-masked]>
Date: Mon, 22 Sep 2003 13:47:46 -0500

Javier,

This was worded non-specifically in the draft, section 4.2.1:

=====
If there is no other User Data message to be sent when there is a
message to acknowledge, M2PA SHOULD send a User Data message with no
data payload. The FSN for this empty User Data message is not
incremented. It MUST contain the same FSN as the most recently sent
User Data message containing Data. This message SHOULD be sent
promptly in order to prevent poor SS7 performance.
=====

Waiting 0.5 sec is way too long. On the other hand, even if there are 
only a few messges (less than 8), it is still not good to wait 0.5 
seconds to ack.

To cover both cases, there would need to be both a time limit and a 
number-of-messages limit.

tomG.

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