Subject: RE: [Megaco] Replies to requests from failed MGC

From: "Tom-PT Taylor" <[email-masked]>
Date: Thu, 23 Aug 2001 10:09:17 -0400

When we did that section 11.5 stuff, it was certainly in my mind that
(assuming shared MGC state), the new MGC would take over from the old at a
certain point, including closing out old transactions.  I can see the catch:
this makes message validation at the MG really messy.  If there was no
shared state, the old transactions would be cleared by resending them to the
new MGC.  Maybe this is the appropriate procedure in all cases and 11.5
should be changed.

-----Original Message-----
From: Terry L Anderson [mailto:[email-masked]]
Sent: Tuesday, August 14, 2001 5:57 PM
To: Megaco Mailing List
Subject: [Megaco] Replies to requests from failed MGC

I hate to open this again.  I believe we have settled this but the IG
does not seem to have a change.

The issue is whether replies to requests from a failed MGC are sent to a
secondary MGC or are sent to the failed MGC (in spite of likely
failure).

We have a number of statements (section 9.1, D.1, D.1.5) all of which
say that replies must be sent to the address and port from which the
request was sent.  I believe we are in agreement that this is a rule
without exception.  But 11.5 pretty clearly contradicts this.
    "Accordingly, commands in progress continue, TRANSACTION REPLIES ARE
SENT TO THE NEW MGC (after a new control association is established),
and the ..."

The context does NOT sound like these replies are only replies to new
requests (which would hardly need to be stated.  And so this seems to
contradict the general principle or suggest an exception to the
otherwise simple rule.  However, D.1.5 seems to be talking about exactly
this same case and follows the general rule.

This discrepancy appears to have been noticed as early as Jan 20, 2000
by Shalini Philip and Brian Rosen's reply of Jan 21, 2000 suggested 11.5
needed to be changed.  I see the same point raised a few more times in
the archives.  And replies always seem to support the general rule.  I
find no support for the 11.5 wording.  But I can find no correction to
this in the IG (if its there could someone point out the item number).

Are we in agreement that this wording is in error and should be changed
to something like:

"Accordingly, commands in progress continue and replies to all commands
from the original MGC must be sent to source address and port from which
they were sent (even if they are likely to fail). The MG should expect
outstanding transaction replies from the new MGC."

Do we still agree with the last sentence (from the last clause of the
original)?  Should the new MGC (if it can) reply to transactions sent to
the failed MGC (this, of course, will  happen only if the MGCs had
shared state)?  These replies can still be sent to the addr/port from
which they came (the MG) and so do not violate the general rule, but
this does seem to fit with the general philosophy (which we would be
changing) that the new MGC is taking over role of original even for
pending transactions.

--
Waiting for the other shoe to drop but hoping its a one legged man.
------------------------------------------------------------
Terry L Anderson              mailto:[email-masked]
Tel:908.582.7013   Fax:908.582.6729
Lucent Technologies/INS/Voice Over IP Access Networks
Rm 2B-121, 600 Mountain Av, Murray Hill, NJ 07974
http://its.lucent.com/~tla (Lucent internal) http://www.gti.net/tla