Re: problem with CMG and one mutual SEND/RCV connection

Hi,

sorry for the delayed response, I just checked the issue again. From my
point of view your description of the way Kannel works proves my observation.
When you get a DLR then you need to ACK this asap instead of sending MTs first,
because CMG (EMI) seems to be waiting for those responses. I think they have
implemented a way of making sure, a connected application is not overloaded
by traffic from CMG (generally, some kind of window size implementation for
the direction smsc->kannel). So if they don't get ACKs soon enough, they just
delay sending. Which eventually leads to exactly the situation I described.
Of course, you can say this does not go along with the protocol, and I agree
with that, but the problem remains the same. For that reason I didn't call
it a bug (as you might have noticed). It's just that I think the lack of
WindowSize parameter in the receive direction made CMG implement a substitute, and
that's what is causing the problem. (At least, that's what I think.)

Kind regards,
Holger.

> Hi again,
> 
> I do not agree here... We doesn't have any queue for ACK's. If emi driver 
> receive DLR's then ACK's will be send immediately back, without any
> queuing 
> (only tcp/ip buffering is here). That means, the right order is always
> there:
> 	1) kannel -> send msg -> smsc 
> 	2) smsc -> send ack -> kannel
> 	3) smsc -> send dlr -> kannel
> 	3) kannel -> send next msg (depends on window size) -> smsc
> 	4) kannel -> send ack -> smsc
> 
> So I can not undestand, why it should happens here ? If it is happens,
> then 
> (imo) CMG has a bug! emi is asynch. protocol and smsc may not wait for any
> 
> ack's before sending ack's back!
> 
> On Monday 04 August 2003 10:59, Andreas Fink wrote:
> > if this is really the case, then we have a bug to fix.
> > Bruno what you think of this?
> >
> > On Montag, August 4, 2003, at 10:55  Uhr, Holger Seiferth wrote:
> > > Hi,
> > > when using kannel with CMG SMSC and a provider which uses one
> > > connection to
> > > do both sending and receiving messages (incl. notification) there
> > > seems to be
> > > a kind of "Dead Lock" problem with sending messages and sending
> > > notifications. Situation is like this (I tried to simplify the
> > > description to make it
> > > easier to understand):
> > > I send 100 messages to Kannel. Kannel puts those 100 messages into its
> > > send
> > > queue. Then it sends out the first 5 messages (assuming WindowsSize is
> > > 5).
> > > Then I get back 5 ACKs and 5 notifications. After I got back the ACKs,
> > > Kannel
> > > sends out the next 5 messages. Then I get back 5 ACKs and 5
> > > notifications, and
> > > so on.
> > > The problem is:
> > > Kannel seems to put the ACKs to the notifications in the same queue as
> > > the
> > > outgoing messages without any priority. So those ACKs are not sent
> > > until the
> > > last of the 100 MOs was sent. But we get into trouble, because the CMG
> > > SMSC
> > > keeps waiting for those ACKs and since they don't come, it's assuming
> > > that our
> > > side (meaning Kannel) is busy, so it delays sending the MT ACKs.
> > > Finally, we get into the situation when Kannel waits for MT ACKs
> > > (because
> > > CMG refuses sending them) and CMG waits for notification ACKs, since
> > > they are
> > > in the Kannel message queue.
> > > I think, to prevent this, Kannel would have to send any ACKs before
> > > sending
> > > any messages, meaning Kannel needs to set a higher priority on ACKs
> > > than on
> > > MTs.
> > > Is there any (configuration) solution for this problem?
> > > Thanks!
> > >
> > > Kind regards,
> > > Holger
> > >
> > > --
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> > Andreas Fink
> > Global Networks Switzerland AG
> >
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> Best regards / Mit besten Grüßen aus Düsseldorf
> 
> Dipl.-Ing.
> Alexander Malysh
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