EMI/UCP bug

There's a bug in EMI which shows up under the following conditions:

a) Kannel is under heavy load.
b) the throughput of the EMI/UCP smsc is limited to a low value


The effect occurs like this:

The EMI/UCP SMSC does throttle to enforce the speed limitations. So the 
ACK's/NACK's will not come in immediately but a bit later.
For example if you have 5 messages a seconds set up, the EMI/UCP SMSC 
will take 200msg to get you the ACK/NACK.

Now Kannel does send additional packets down the same pipe because of 
windowing. And they get delayed even further.
The problem starts when those cumulated delays become larger than 60 
seconds (or whatever timeout you define). Then Kannel presumes your SMS 
didnt get there and sends it again. Usually it was getting there but no 
ACK/NACk was received yet due to enforced speed limit of the SMSC. So 
the result of all this is SMS duplications in masses.

There's a speed limit factor in Kannel which lets it wait after a 
submission a certain time. However this one doesn't work because new 
incoming SMS on bearerbox do wake up the thread to continue. This is 
relatively easy to fix.

But ther's another issue. Windowing. Usually if you set windowing to 4 
or similar value, kannel should not submit more than 4 outstanding 
messages and then wait for ACK/NACK. In this scenario, Kannel should 
never ever get to the point where the ACK/NACK's cumulate to values 
above 60 seconds but only to 4x the throughput delay, in our 5msg/sec 
example  with windowing set to 4 that would be 0.8s.

So there's definitively something wrong. We have seen this problem in 
our setup and I've heard from other Kannel users having similar 
problems with other SMSC's from other carriers.

I will look into this bug more seriously now. If anyone has a few good 
hints, let me know.



Andreas Fink
Global Networks, Inc.

------------------------------------------------------------------
Tel: +41-61-6932730  Fax: +41-61-6932729   Mobile: +41-79-2457333
Global Networks, Inc. Schwarzwaldallee 16, 4058 Basel, Switzerland
Web: http://www.global-networks.ch/      [email protected]
------------------------------------------------------------------
Member of the GSM Association