This is definitely a race condition and will be very hard to reproduce.  
If the calling UA got confused (or actually supports adhoc conferencing 
multiple early media channels) due to a fork then you will get exactly 
what you have experienced.  The trick is both 200 Ok must be close 
enough to each other so as not to generate a CANCEL to one of the 
transactions.

A couple of questions to determine if it's a case of a UA confused by 
fork or a cool UA feature supporting multi channel forks:

1.  is the audio heard by C and A full duplex?  Meaning (C and A can 
talk to each other)
2.  Can both C and A be heard by B?

if the answer to both Q's is yes, then you got a very cool UA.  Send in 
the brand.

On 08/12/2011 09:01 PM, Fulvio Scapin wrote:
> Hello to everyone.
> Just wishing to report a strange accident occured to me some time ago
> (so forgive me were the details a bit vague), mostly out of curiosity
> about possible similar experiences.
> A small orientation about my setup:
> FreeSWITCH as a B2B UA connected to serveral ITSPs, upstream from a
> SipXecs proxy, redirecting incoming calls to an auto-attendant
> embedded in SipXecs.
>
> The strange event happened as follows:
>
> * incoming calls directed to a hunt group of SipXecs after exiting the
> default auto-attendant
> * phone A not in the hunt group, phones B and C in the hunt group
> * phones B and C ring
> * phone A tries to pick up the call with *78 and extension B
> * simultaneously phone C picks up the call
>
> Result:
> the two sides of the call are heard by both C and A, as if, for
> instance, one was monitoring C's call using phone A .
>
> Since call monitoring isn't a built-in feature of SipXecs (and my boss
> said 'I want that' as soon as we understood what had taken place), I
> was wondering whether mine was a freak accident or something more
> promising.
>
> Regards,
> Fulvio Scapin
> _______________________________________________
> sipx-users mailing list
> [email protected]
> List Archive: http://list.sipfoundry.org/archive/sipx-users/
>

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