[SR-Users] Wrong ACK to Provider

[Daniel-Constantin Mierla]

On 28/08/14 15:11, Olle E. Johansson wrote:
>
> On 28 Aug 2014, at 14:57, Daniel-Constantin Mierla <miconda at gmail.com 
> <mailto:miconda at gmail.com>> wrote:
>
>>
>> On 28/08/14 14:45, Olle E. Johansson wrote:
>>>
>>> On 28 Aug 2014, at 14:14, Yuriy Gorlichenko <ovoshlook at gmail.com 
>>> <mailto:ovoshlook at gmail.com>> wrote:
>>>
>>>> Hello. I try to provide call scheme:
>>>>
>>>> internal client  -> asterisk -> Kamailio -> provider -> external 
>>>> endpoint call
>>>>
>>>> when I make call I see this:
>>>>
>>>> asterisk     kamailio   provider
>>>> invite -->       invite -->
>>>>                                 <--     407
>>>>                        ACK   -->
>>>>                        invite w/Auth -->
>>>>               <--    100  <--    100
>>>>               <--    180  <--    180
>>>>               <--    183  <--    183
>>>>                <--    200  <--      200
>>>>    ACK  -->   ACK  -->
>>>>
>>>> My problem with last ACK, that I send to provider. Provider ignores 
>>>> it, and sends me some OK packets. As resultI can notend session ( 
>>>> answer to BYE 481 - transaction does not exists). I think it is 
>>>> wrong ACK but can not undrtand where I do mistake.
>>> Well, by letting the proxy handle authentication the INVITE 
>>> tranction i closed without Asterisk knowing about it. So the ACK 
>>> sent from the proxy and from Asterisk is for the same transaction, 
>>> which messes things up. Asterisk does not know anything about the 
>>> second invite. Letting the proxy handle authentiction breaks the SIP 
>>> protocol in bad ways and is generally not a good solution.
>>> You may want to send another response to asterisk when you get the 
>>> 407 so Asterisk retries and use the retry as a trigger for the 
>>> second INVITE and add auth to that.
>> While breaking the cseq incrementation for authentication (mentioned 
>> in the readme of uac), the Asterisk seems to do ok here, because the 
>> ACK is coming from asterisk, but it is not accepted by the provider.
> You are missing the fact that the ACK sent by Asterisk is already sent 
> by the proxy. The INVITE w/AUth have a different cseq than the ACK.
Kamailio is doing serial forking in this case, so the first ack is for 
the first branch that gets 407. This should be as usual for 
serial/parallel forking.

Then, Kamailio is not increasing the cseq here -- that's the limitation 
with uac auth module, because the authenticator should normally reject 
it. But if it is authentication against another kamailio, should just work.

>>
>> The provider (having a plivo platform, based on the responses) is 
>> running kamailio 4.1.2 in front (looking at 100 trying).
>>
>> Authentication from kamailio to another kamailio using uac module 
>> should work fine, as kamailio doesn't act as end user UAC and doesn't 
>> care much of cseq.
> Won't the second ACK on the same transaction just be ignored, while it 
> waits for an ACK on the new transaction?
It is the same transaction in this case, just two branches from kamailio 
downstream, which is serial forking case, as mentioned above.

Cheers,
Daniel

-- 
Daniel-Constantin Mierla
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
Next Kamailio Advanced Trainings 2014 - http://www.asipto.com
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