Subject: [Sigtran] SIGTRAN Plugtest Day 4

From: "Barry Nagelberg" <[email-masked]>
Date: Fri, 20 Apr 2007 10:39:08 +0400

Greetings from Moscow! Here is the wrap-up report for Day 4 of the SIGTRAN
Plugtest.

Protocols tested:
M2PA - 4 implementations
M3UA - 7 implementations
M2UA - 5 implementations
SUA  - 5 implementations

There was one issue raised at the Day 4 wrap-up. The issue is a case of
non-interoperability that has been observed between 2 fielded
implementations, and has already been discussed on the mailing list (see
"Question related with DAUD Message" from Jan 31 - Feb 2 2007).

The specific issue that was raised on the mailing list concerns one
implementation sending 1024 instances of the same parameter in a DAUD msg,
and another implementation not prepared to accept so many instances of the
same parameter.

The broader issue is that there is no specified limit on the size of an xUA
message, or a limit on the number of times a single parameter may be
repeated in a msg. In order to protect itself from running out of memory
resources, each implementation is setting ad-hoc limits on what it is
willing and able to receive. By their nature, these ad-hoc limits are all
different, and we have wound up with non-interoperability issues.

The lack of response from the xUA editors on this issue has been
disapointing, and there is concern among the group that this issue isn't
being addressed. Several options to address this issue were suggested during
the wrap-up meeting:

1. Allow unlimited repetition of individual parameters, but set an upper
limit on the total size of a non-data msg. The suggested limit is 8096
bytes.

2. Add functionality to the specs to allow the xUA endpoints to negotiate
the max non-data msg size during startup.

3. Use the maximum transmission unit (MTU) size obtained via SCTP "Path MTU
Discovery" to set the limit on the total size of a non-data msg.

Barry Nagelberg

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