Notices to ASPTM message mapping

Hello,

I would like to share any findings we have made during implementation of
SUA in IPSP environment. Our work has been based on RFC 3868 and
draft-ietf-sigtran-sua-implementor-guide-03.txt. Please send comments if
you find out we are not true.

 

1) Problem with mapping of ASPTM messages on SCTP stream. - Which stream
number to use? ... there are two relevant paragraphs in RFC 3868,
sua-implementor-guide-03 does not solve this question.

RFC 3868, section 4.2.1:

"All non-Transfer messages, with the exception of ASPTM, BEAT and BEAT
Ack messages SHOULD be sent on SCTP stream '0'.  ASPTM messages MAY be
sent on one of the streams used to carry data traffic related to the
Routing Context(s), to minimize possible message loss."

RFC 3868, section 4.3.4.3:

"It is possible for the ASP to receive Data message(s) before the ASP
Active Ack message as the ASP Active Ack and Data messages from an SG or
IPSP may be sent on different SCTP streams.  Message loss is possible,
as the ASP does not consider itself in the ASP-ACTIVE state until
reception of the ASP Active Ack message."

 

So ASPTM messages MAY be sent on any SCTP stream, but generally it is
better to send they on any traffic stream (not on SCTP stream 0). It
practically means, a sending entity MAY send it on any SCTP stream and a
receiving entity SHOULD be prepared to receive it on any SCTP stream.

 

2) Mapping of ASPTM Ack messages on SCTP stream ... I think it is
general principle to be received message acknowledged on the same stream
as an acknowledged message has been received - but this general
principle is not enforced in RFC 3868 or
sigtran-sua-implementor-guide-03. This situation may leads to the
situation following the next example:

------------ ASP Active/SCTP stream 1 ----->

<-------- ASP Active Ack/SCTP stream 0 ----

 

Thanks for comments

Jan

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