Subject: [Sigtran] M2PA Comment -- How do M2PA peers resynch seq nos after processor outage?

From: [email-masked]
Date: Wed, 17 Jul 2002 08:04:27 -0400

Hello All,

I would like to see the M2PA draft clarify the processor outage procedure,
and
specifically the resynchronization of sequence numbers after the outage
clears.

Since, according to the draft, the node experiencing the outage "stops
receiving",
I am assuming that it merely picks up where it left off when the outage
clears.

The fact that the M2PA adapter layer performs ACKs but lacks the capability
to
retransmit makes the implementation of this procedure a challenge. By the
time
the far end gets the Link Status Processor Outage message, plenty of
un-ACK'd
user data is on the wire and in the SCTP layer of the node experiencing the
outage. How does the local outage node know what to do with this data after
resuming? Depending on duration of the outage, this user data could already
have been rerouted, and therefore should be discarded. Implementing T7
(excess delay of ACK) is a further complication.

I propose that rather than stopping receiving, the outage node continues to
receive, but discards all user data (no BSN update), during the outage.
When
the outage clears,  it sends a LSPOE with the latest FSN and BSN. The
far-end,
upon receiving LSPOE, sets its FSN and BSN to match, and then retransmits
from its retransmit queue based on the peer's BSN. It is possible that the
retransmit queue will be empty, if retrieval or flush occured. T7 is
disabled
during processor outage.

Regards,

Jeff

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---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Wed, 17 Jul 2002 18:05:00 -0600

Jeffrey,

Huh?  When MSUs are not ACKed they are held in the sending M2UA's buffers
for retranmission on a new association (or alternate link).  Should the
link ultimately fail as a result of SIPO, these messages will be flushed
or diverted to the alternate link.  If SIPO clears, there is nothing stopping
the sender from picking up where it left off.  I do not see the need for
more procedure.

--brian

[email-masked] wrote:                       (Wed, 17 Jul 2002 08:04:27)

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