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[reSIProcate] Duplicate transaction ids on Windows

From: Robert Mansfield <RJM@xxxxxxxxxxxxxxx>
Date: Wed, 21 Dec 2005 19:04:59 -0000

Title: Message

All,

I've read through the previous correspondance on this issue and am hoping someone can clarify the best practice for a multithreaded application on widows. In particular the use of the 'Random' class for generating unique transaction ids.

I'm running two windows applications on seperate hosts, one acting as a UAC, the other a UAS. There are 60 simumtaneous dialogs being created.

During load testing I submit a BYE request to the stack but the stack doesn't transmit the message to the wire, claiming the transaction id already exists in the transaction map.

The application has two threads, one processing SIP messages from the stack (g_SipStack->receive()) and the other thread sending messages to the stack (g_SipStack->send(sipMessage). The stack object is global to both threads, but only one thread is responsible for creating and submitting SIP requests.

On the UAC side I have seen a duplicate transaction ids submitted to the TransactionManager from the application, typically a BYE is discarded because the tid has been used for an ACK from a different dialog.

In the creation of both the ACK and the BYE message the 'via' header branch parameter is instantiated with a call to "via.param(p_branch)".

In this particular stack trace instance the transaction id appears to have been added from a received response, here is a fragment from the stack trace:

####################################################################################################################

To: <sip:P335544401223@xxxxxxxxxx>;tag=3c6fe50d

From: <sip:DNX_TESTC2P8@xxxxxxxxxx>;tag=9b540c2f

Via: SIP/2.0/UDP 10.0.0.212:5060;branch=z9hG4bK-d87543-8664a730b52dc246-1--d87543-;rport

Call-ID: 4767b466384e6543@UmVkVk9JUA..

CSeq: 2 BYE

Content-Length: 0

#####################################################################################################################

So I guess I have two questions:

a) if two resiprocate applications are running back to back would a received tid (generated remotely for dialog A) confuse the stack when submitting a request with the same tid generated locally for dialog B (branch parameter unique across space and time)?

b) just how random is the tid generated via the Random class. Should I expect so many 'duplicates' after running just one iteration of the test?

Regards,

Rob Mansfield.

============================

Robert Mansfield

Senior Software Engineer

Redwood Technologies Limited

Tel +[44] (0)1344 304 344

Fax +[44] (0)1344 304 345

E:mail mailto:rjm@xxxxxxxxxxxxxxx

Web http://www.redwoodtech.com

============================

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