Very hard to say without a complete ngrep trace. If both parties are on public IPs, there is probably something with the signalling, not the SDP payload.  The 183 Session Progress is a so-called provisional reponse. It can be used for early media (to set up the rtp stream before connection).  A double 183 sounds strange if it's the proxy that does it.

g-)

 

---- Original Message ----
From: Sam Lee
To: serusers@lists.iptel.org
Sent: Monday, July 25, 2005 12:27 PM
Subject: [Serusers] 1 way voice issue

> Hi,
>
> I've recently encountered some problem with my SIP service whereby i
> call out to a specific number and i encounter a one way voice. If i'm
> the initiator, i cannot hear the other party but he can hear me. At
> first i thought it was a return route issue (as i'm going thru NAT) ,
> so i switch my SIP to a public IP but i still face the same problem.
> Its really only that specific PSTN number that i have dialed facing
> this problem. The only difference that i can think of is that PSTN
> number is on a different route. I did a NGREP from my SIP server for
> the PSTN number that works (2-way voice) and the Number that doesn't
> work (1-way voice) . The only difference is there is an extra :     
>
> NGW --> Proxy
>   SIP/2.0 183 Session Progress..Via: SIP/2.0/UDP
> Proxy --> SIP Device
>   SIP/2.0 183 Session Progress..Via: SIP/2.0/UDP
>
>
> for the PSTN number that works (the one with 2-way voice).
>
> Anyone has idea what does the Session Progress is for ? Or what
> problem am i facing ?
>
> Thanks a mILLION !
>
> Regards,
> Sam
>
>
>
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