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@200.68.89.10
192.168.0.101:23018:audio 200.68.89.2
200.68.89.10 remote
200.68.89.10 unknown AddPac=20SIP=20Gateway
info=from:1150316660@200.68.89.10,
to:1152464490@200.68.89.10,fromtag:3512844671,totag:7b07717a4
proxydispatcher[30535]: warning: trying to lookup session with non-existent id: '
2281401749@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