[OpenSIPS-Users] [OpenSIPS-Devel] Why the best response is 408 instead of 486 when parallel forking?

[Klaus Darilion]

Dan Pascu wrote:
> On Monday 27 October 2008, Iñaki Baz Castillo wrote:
>> 2008/10/27 Iñaki Baz Castillo <ibc at aliax.net>:
>>>> I do not think that 6xx should be considered before 4xx or 3xx. 6xx
>>>> means global response and if you get a 4xx and a 6xx at the same
>>>> time, it is obvious that a device took a global decision that
>>>> another device doesn't agree upon. 6xx should only be sent when a
>>>> device knows _for sure_ that no other device can answer a call and
>>>> it can give a final answer in the name of all devices (which is
>>>> practically almost never when you have parallel forking).
>> I understand what you say. You are talking about devices that decide
>> to reply a 6XX. An endpoint should never sent a 6XX (since it could
>> also break sequential forwarding to a voicemail server for example),
>> but the fact is that, in terms of RFC 3261, a 6XX must break parallel
>> and serial forking and must be chosen as winner reply.
> 
> It doesn't matter who sends the 6xx (device, proxy, gateway, ...). Once 
> you use parallel forking, 6xx should never be used IMO. 6xx means that 
> some device/proxy/gateway _knows_ that _no other device_ can answer the 
> call for whatever reason. Now if you used parallel forking and you also 
> receive a 4xx/3xx from another device, than it is obvious that the other 
> device didn't agree with the assumption the first device made. Which 
> means that the 6xx reply was a bad assumption. Even more, at some point 
> you cannot know if an upstream device did parallel forking or not. So 
> even if you are sure you do not do parallel forking and you can assume 
> you know there is a final global 6xx answer, you have no idea if that 
> won't clash with a 3xx/4xx somewhere upstream.

I wonder how there can be a clash (except in race conditions)? If one 
branch replies with 6xx, the other branches will be canceled (at least 
they should be cancelled).

regards
klaus