Re: PRACK: Does non-200 response cease re-transmission of reliable 18x?

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Hi, 

>That's a good scenario. Any others?
>
>The point of the PRACK is to indicate to the UAS that the 1xx it sent was received successfully. Unless its a 401 to the 
>PRACK, I don't see any other reason why the UAS should continue retransmitting the 1xx if its sent a non 2xx reponse to a 
>PRACK. The PRACK has served its purpose.
>
>Having said that, what other reasons would a UAS reject a PRACK?

Well, rejecting an SDP offer is one use-case we've discussed.

The PRACK could also be rejected due to some overload situation etc.

Regards,

Christer



2009/4/1 Paul Kyzivat <pkyzivat@xxxxxxxxx>:
>
>
> Christer Holmberg wrote:
>>
>> Hi,
>>
>> One of the PRACK related issues presented in SFO is whether a PRACK 
>> non-200 response would cease re-transmission of the assoicated 
>> reliable 18x response.
>>
>> Based on the mail discussions we've had I proposed that the non-200 
>> response DOES NOT ceasee the re-transmission. However, some people 
>> seemed to have an issue with that, so I was asked to "take it to the list".
>>
>> The main justification why a non-200 response would not cease the 
>> re-transmission is because an intermediate may reject the PRACK, in 
>> which case the UAS will never receive it (read: the UAS will continue 
>> to re-transmit the reliable 18x). So, when the UAC receives the PRACK 
>> non-200 response it should send a new PRACK, which hopefully will 
>> reach the UAS and trigger a 200 response.
>>
>> So, anyone who does not agree with the justification aboive, and 
>> thinks that a non-200 response DOES cease the re-transmission of the 
>> associated reliable 18x response, please indicate so.
>
> I agree with Christer here. Another scenario where this would be 
> important
> is:
>
> -> INVITE
> <- 180rel
> -> PRACK
> <- 401
>
> It this case it is essential to retry the PRACK with updated credentials.
> Certainly the UAS doesn't want to consider the 180 to have been 
> acknowledged in this case, since it might have been from a MiTM.
>
> This could come about in the case of a reINVITE, where the nonce used 
> in the original INVITE finally becomes stale by the time the PRACK is received.
>
>        Thanks,
>        Paul
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