Subject: Re: Washington Issue 13 - Receipt of Duplicate Request when Pendi ng

From: Brian Rosen <[email-masked]>
Date: Wed, 17 Nov 1999 07:42:33 -0500

The text already recommends a timer.  The timer is what would
trigger a duplicate request.  A similar timer would have to
trigger a duplicate reply (although it's on the responder
side, the first timer is on the initiator side).

The issue here is the time to retain the reply when using a
reliable transport.  Usually, TCP will not lose a packet.
As we all know, there are situations where something gets dropped
between two applications, and we don't need to point fingers.
Hence we recommend the timer, and we recommend that you keep
responses.

Still want to make sure we agree that it is NOT a REQUIREMENT
that the responder send a Pending upon receipt of a duplicate
Request.

Brian

> -----Original Message-----
> From: Paul Hollis [mailto:[email-masked]]
> Sent: Wednesday, November 17, 1999 3:01 AM
> To: Brian Rosen
> Cc: [email-masked]
> Subject: Re: Washington Issue 13 - Receipt of Duplicate Request when
> Pending
>
>
> Hi Brian,
>
> don't we want H.248 to be independent of the underlying transport?
> Therefore, we would probably want a timer in the protocol, perhaps
> set to similar values as the underlying transaport timers, but still
> independent.
>
> What if we were to just store a copy of the transaction IDs
> for this certain
>
> period, and if a transaction comes in with a transaction ID
> that we have
> stored
> then we just discard it. I would assume the MGC would end up
> resending the
> request
> again if it needed to. Whereas if it was a case where the
> REPLY and the
> re-REQUEST "passed in the night" the MG would have got the
> reply and no
> re-REQUEST is needed.
>
> Once the period expires then transaction should be treated as new
> transactions
> and be serviced as normal.
>
> Your thoughts?
>
> Regards Paul.
>
> Brian Rosen wrote:
>
> > It simply keeps a copy of the reply.  It DOES NOT rerun the
> > transaction.
> >
> > If UDP/ALF is the transport, you keep them until you get
> > the TransactionAck
> >
> > If TCP is the transport, you probably keep them for something
> > longer than the TCP timeout (someone have a more precise
> > idea?)
> >
> > Brian
> >
> > > -----Original Message-----
> > > From: Paul Hollis [mailto:[email-masked]]
> > > Sent: Tuesday, November 16, 1999 10:16 AM
> > > To: Brian Rosen
> > > Cc: [email-masked]
> > > Subject: Re: Washington Issue 13 - Receipt of Duplicate
> Request when
> > > Pending
> > >
> > >
> > > Hi Brian,
> > >
> > > does this mean the MG would execute the transaction again, or
> > > does the MG need some sort of memory of recent replies sent?
> > >
> > > Even if the MG were to discard it, the MG would need to have some
> > > memory of previous transactions, to know that this transaction
> > > had already been executed. Perhaps the MG has a certain time
> > > period for which it remembers recent transactions, after which
> > > it assumes the transaction is a new/different one and it can
> > > execute it.
> > >
> > > Regards Paul.
> > >
> > > Regards Paul.
> > >
> > > Brian Rosen wrote:
> > >
> > > > I think that a duplicate request after sending a reply
> > > > could mean the reply was lost.  The responder should repeat
> > > > the reply.  Of course it could be that the duplicate request
> > > > and the reply passed in the night, but sending a duplicate
> > > > reply would not hurt.
> > > >
> > > > Brian
> > > >
> > > > > -----Original Message-----
> > > > > From: Paul Hollis [mailto:[email-masked]]
> > > > > Sent: Tuesday, November 16, 1999 9:07 AM
> > > > > To: Brian Rosen; MEGACO Mailing list
> > > > > Subject: Re: Washington Issue 13 - Receipt of Duplicate
> > > Request when
> > > > > Pending
> > > > >
> > > > >
> > > > > Hi Brian,
> > > > >
> > > > > Along a similar line:-
> > > > >
> > > > > what happens if a MG sends a REPLY to a transaction
> and then gets
> > > > > a REQUEST with the same Transaction ID. Does it treat
> > > this as a new
> > > > > transaction and service it or does it assume that it is a
> > > > > repeat of the
> > > > > original one and discard it (ie. the MGC resent the
> > > transaction just
> > > > > as the MG was sending the reply)?
> > > > >
> > > > > Regards Paul.
> > > > >
> > > > >
> > > > > Brian Rosen wrote:
> > > > >
> > > > > > A number of issues were raised in the Washington
> meeting that
> > > > > > were "send to the list".  This is one of these
> issues, with the
> > > > > > problem and my suggested fix.
> > > > > >
> > > > > > Problem:
> > > > > > What should the initiator do when it has sent a "pending"
> > > > > > response, but receives a duplicate request.
> Possible answers
> > > > > > are: send another pending immediately, or wait for
> the normal
> > > > > > timeout and send pending.
> > > > > >
> > > > > > Proposed Solution
> > > > > > Since the timeout of the original pending must be less than
> > > > > > the timeout of the duplicate, the responder will see
> > > > > > the 2nd pending response within it's timeout
> window.  Therefore,
> > > > > > it is not necessary to respond with an extra pending.
> > > > > >
> > > > > > It should be noted that there is no harm in sending
> extra pends.
> > > > > >
> > > > > > Also note that if the responder finishes within the timeout
> > > > > > of the first pend, sending the ack (or error) will satisfy
> > > > > > the original request and the duplicate.
> > > > > >
> > > > > > Brian
> > > > >
> > > > > --
> > > > >
> > > > > oooooooooooooooooooooooooooooooooooooooooooooo
> > > > >   Paul Hollis
> > > > >   Ericsson Eurolab Deutschland GmbH
> > > > >   Ericsson Allee 1
> > > > >   D-52134 Herzogenrath
> > > > >   Germany
> > > > >   Phone: +49 2407 575 8092
> > > > >   email: [email-masked]
> > > > > oooooooooooooooooooooooooooooooooooooooooooooo
> > > > >
> > > > >
> > >
> > > --
> > >
> > > oooooooooooooooooooooooooooooooooooooooooooooo
> > >   Paul Hollis
> > >   Ericsson Eurolab Deutschland GmbH
> > >   Ericsson Allee 1
> > >   D-52134 Herzogenrath
> > >   Germany
> > >   Phone: +49 2407 575 8092
> > >   email: [email-masked]
> > > oooooooooooooooooooooooooooooooooooooooooooooo
> > >
> > >
>
> --
>
> oooooooooooooooooooooooooooooooooooooooooooooo
>   Paul Hollis
>   Ericsson Eurolab Deutschland GmbH
>   Ericsson Allee 1
>   D-52134 Herzogenrath
>   Germany
>   Phone: +49 2407 575 8092
>   email: [email-masked]
> oooooooooooooooooooooooooooooooooooooooooooooo
>
>