[Serusers] Re: 200 OK/SDP and ACK/SDP problem

[Carla Ares]

>
> Hi all,
> I have a problem with audio, when the destination of a call is natted and
> the other side is public. This problem is cause because the SDP info only is
> present in the 200 OK and in the ACK message.
>
> I'm using ser (8.14) with mediaproxy (1.2.1).
>
> I have an H323 to SIP translator (and SIP to H323 too) connected to the
> PSTN and to the SIP Proxy (SER).
> H323 is the origin of the call (public client), and SIP UAC is the
> destination (Natted client).
> My proxy is working in state full mode and has a public IP.
>
> The H323 side is using slow start, so when it starts the transaction with
> an INVITE, it will not send the SDP info (it will send it in the ACK
> message).
> The proxy forwards this message to the destination.
> SIP UAC, starts ringing. When we hooks off, the SIP UAC send an 200 OK
> with SDP message to the H323 side.
>
> This is the 200 OK / SDP that the proxy receives from the SIP side.
>
> No.     Time        Source                Destination           Protocol
> Info
>     488 28.488811   200.68.89.2           200.68.89.12          SIP/SDP
> Status: 200 OK, with session description
>     Message body
>         Session Description Protocol
>             Session Description Protocol Version (v): 0
>             Owner/Creator, Session Id (o): 700600 6015 6015 IN IP4
> 192.168.0.101
>                 Owner Username: 700600
>                 Session ID: 6015
>                 Session Version: 6015
>                 Owner Network Type: IN
>                 Owner Address Type: IP4
>                 Owner Address: 192.168.0.101
>             Session Name (s): AddPac Gateway SDP
>             Connection Information (c): IN IP4 192.168.0.101
>                 Connection Network Type: IN
>                 Connection Address Type: IP4
>                 Connection Address: 192.168.0.101
>             Time Description, active time (t): 0 0
>                 Session Start Time: 0
>                 Session Stop Time: 0
>             Media Description, name and address (m): audio 23018 RTP/AVP
> 18 8 0 101
>                 Media Type: audio
>                 Media Port: 23018
>                 Media Proto: RTP/AVP
>                 Media Format: ITU-T G.729
>                 Media Format: ITU-T G.711 PCMA
>                 Media Format: ITU-T G.711 PCMU
>                 Media Format: 101
>
> Following the ser.cfg, this 200 OK / SDP will make the proxy to use
> mediaproxy (use_media_proxy()), because the destination user is natted. So
> the mediaproxy module, will generate a lookup command to the
> proxydispatcher.py.
>
> proxydispatcher[30535]: command lookup 2281401749 at 200.68.89.10
> 192.168.0.101:23018:audio 200.68.89.2 200.68.89.10 remote 200.68.89.10unknown AddPac=20SIP=20Gateway info=
> from:1150316660 at 200.68.89.10,to:1152464490 at 200.68.89.10
> ,fromtag:3512844671,totag:7b07717a4
> proxydispatcher[30535]: warning: trying to lookup session with
> non-existent id: '2281401749 at 200.68.89.10'
>
> The proxydispatcher does not recognize that command because it has not
> generate the session before. So, the proxy forwards the 200 OK /SDP message
> without changing the SDP info. When the H323 sides receives that info, it
> thinks that it has to send RTP to the private IP.
>
> Then the H323 sends the ACK with SDP.
>
> Then, we cannot ear audio in both sides.
>
> Here is the problem, because, I didn't receive an INVITE with SDP that can
> create the session into the dispatcher.
>
>
> A is public, B is natted
>
> side A            Proxy            side B
>
>     INVITE without SDP
>     ---------->
>     100 Trying
>     <----------
>
>                 INVITE without SDP
>                 ---------->
>
>                 100 Trying
>                 <----------
>                 180 Ringing
>                 <----------
>     180 Ringing
>     <----------
>
>                 200 OK SDP (B private IP)
>                 <----------
>             *1*
>     200 OK SDP (B private IP)
>     <----------
>
>     ACK SDP (A public IP)
>     ---------->
>             *2*
>                 ACK SDP (mediaproxy public IP)
>                 ---------->
>
> ......................................................
>             RTP from B
>             <----------------------
>     *3*
> ......................................................
>
>
> *1* The proxy must replace the private IP of the SDP, with the ip of the
> mediaproxy. The looku prequest does not work, because no session was found
> *2* the proxy generates the session in the mediaproxy. So B thinks that
> the RTP must go to the mediaproxy. But A never knows the mediaproxy address.
> *3* RTP from A goes to anywhere, because A does not know where it is the
> private adrress of B.
>
>


Do you know a solution to this? Is the sequence of the message all right?


Regards.
Carla
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