Re: Processor Outage and Resynchronizing Sequence Numbers

Brian,

Excuse me for using a brand name in my email, I meant no disrespect to
the product I named.

I am running test 3.4.1-1 from the M2PA Test 08 Specification.  After
the exchange of READY messages of step (12) synchronization is not
happening at SP B and the Data Messages from SP B are sent with, what SP
A considers to be, an invalid FSN.  SP A is discarding the data messages
and SP B takes the link Out-of-Service due to T7 excessive delay of ACK.

SP A   READY BSN 1 FSN 1     --------------->
                             <---------------  SP B   READY BSN 1 FSN 3
                             <---------------  SP B   Data Msg. BSN 1
FSN 4
SP A   Data Msg. BSN 1 FSN 2 ---------------->
                             <---------------  SP B   Empty Data Msg.
BSN 2 FSN 4
                             <---------------  SP B   Link Status OOS

My understanding is that the Data Message from SP B after the exchange
of READY messages should have an FSN of 2.  SP A is discarding both the
Data Message and the Empty Data Message.

Best regards,
Martin


-----Original Message-----
From: Brian F. G. Bidulock [mailto:[email protected]] 
Sent: Monday, February 23, 2009 5:02 PM
To: Hecht Martin
Cc: [email protected]
Subject: Re: [Sigtran] Processor Outage and Resynchronizing Sequence
Numbers

Martin,

Please don't use brand names on this list.

"if this is required by MTP2"

Resynchronization is required by ITU-T Q.703 1996,
ETSI EN 300 008-1, and ANSI T1.111.3/2000.

However, I am a little bit confused as to why you
think that the one end synchronizing and the other
end not will cause a problem.  Could you provide
a message sequence chart for what you think the
problem will be?

--brian

Hecht Martin wrote:                           (Mon, 23 Feb 2009
11:41:15)
> 
>    To the mailing list,
> 
>    In the M2PA RFC it details how to resynchronize sequence numbers
after
>    LPR/RPR as follows:
> 
>    M2PA (at both the LPO and RPO ends) uses the BSN value in the
>        received Link Status Ready message to resynchronize its
sequence
>        numbers, if this is required by MTP2.
> 
> 
>    The problem is the "required by MTP2" issue.  If one side
>    resynchronizes its FSN to the BSN received in the READY message,
but
>    the other side didn't implement this, then the FSN on the next MSU
>    received would be wrong and the MSU will be discarded.
> 
>    For example, I am running M2PA conformance tests against the INET.
It
>    doesn't resynchronize its FSN to the incoming BSN as described
above.
>    So the next FSN sent by the Inet is not expected and is discarded.
> 
>    So, the question is, is the resynchronizing really optional?  Or am
I
>    misunderstanding the meaning of synchronize and the FSN is not set
to
>    the BSN of the incoming READY message?
> 
>    Thanks,
> 
>    Martin
> 
>    Martin Hecht
>    Engineering
> 
>    Signaling Core Group
>    Comverse
>    Office: +856 608-2712
>    [1][email protected]
>    [2]www.comverse.com
> 
> References
> 
>    1. mailto:[email protected]
>    2. http://www.comverse.com/

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