[SR-Users] Absorbing ack's

Daniel-Constantin Mierla miconda at gmail.com
Thu Mar 15 23:29:19 CET 2012


Hello,

On 3/15/12 9:48 AM, Egbert Groot wrote:
> Hi all,
>
> I'm having an issue with ACK's being proxied. When an INVITE first comes in (new transaction, new dialog), I do a 'www_challenge(...)'. This makes the proxy send a '401 Unauthorized' reply. The client acknowledges this reply with "ACK". This ACK is 'absorbed' by the proxy.
>
> When during an established call/dialog the client sends an INVITE to set the call on hold, this is an in dialog INVITE (with to-tag etc). Although authentication for this INVITE isn't very necessary, my script does 'www_challenge' anyway. The proxy sends '401 Unauthorized', the client responds with 'ACK'. This ACK however is not 'absorbed' as it should be, but forwarded/proxied (or at least handed over to the routing script). Is this intended behaviour? If so, how can I recognize this ACK to be able to drop it?
>
> I found some related info in this email thread: http://lists.kamailio.org/pipermail/devel/2008-December/017246.html but doesn't discuss this exact issue.
>
> Though this isn't a big problem for me (the upstream gateway ignores the ack, and I can disable authentication for re-invite's), I'm curious why the proxy behaves this way. Hopefully someone can enlighten me.
do you create transaction before doing authentication in second case? 
ACK is absorbed transparently by sl module for stateless reply and they 
get to config and absorbed by tm with t_relay() if it is an ACK for a 
stateful reply.

So, even if it gets to config, does it get relayed? If yes, can you post 
an ngrep trace of such case?

Cheers,
Daniel

-- 
Daniel-Constantin Mierla
Kamailio Advanced Training, April 23-26, 2012, Berlin, Germany
http://www.asipto.com/index.php/kamailio-advanced-training/




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