[Serusers] protocol fixup: missing ACK after 200 OK

[Maxim Sobolev]

That would be a very wrong thing to do, since calee will have no way to 
tell if no-ACK situation has been caused by the loss of 200 OK in 
transit, in which case it has to re-transmit 200 OK, or by the b0rken 
UAC, that don't send ACK after receiving 200 OK. Therefore, such "fixup" 
will undermine non-broken UAs in the presence of packets loss, which is 
unavoidable in the case when UDP is used.

The only way to address this problem is to seek resolution from the 
phone vendor.

Regards,

Maxim

Jamie Yukes wrote:

> I have a user agent that does not ACK after 200 OK.
> Is it possible to configure SER  to generate an ACK and reply to 200 OK?
> 
> broken UA   ---- INVITE ---> ser 
>                    <---- 100 ------- ser ---- INVITE ---> gateway
>                            183                    183 
>                                         ser <--- 200 OK---- gateway
> broken UA  <---- 200 -----     ser
>                       <------ 2 way RTP ----------->
> 
> Call is mostly established, but broken UA does not ACK the 200 OK.
> Can we generate the following packet?
>                                          ser --- ACK ---> gateway
> 
> This would allow the broken UA to interop.
> Can SER generate this ACK?
> 
> Thanks,
> Jamie Yukes
> 
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