[SIPForum-discussion] One Way speech During the Initial Few seconds

[Vivek Batra]

Hi,
I have also observed the same thing lot of times. 
What i understand the rootcause of this is your device is sitting behind the
NAT router (as you have specified) and if we assume that you don't use any
STUN mapping or static IP mapping, then your device will send only private
IP address (10.0.32.2) in SDP body of INVITE.
Now when call is answered by callee on PSTN and three way signaling
establishes, your device has a public IP address to reach to Provider. But
provider has only Private IP address of your device.
So in that case your Provider waits for the RTP packets sent by your device
to Provider, then your Provider retrieves the Network Layer IP Address (and
UDP Port) and sent the packets back to retrieved IP Address instead what you
sent in the SDP body. That is Symmetric RTP! This will enable your NAT
router to send packets back to your device. But in the meanwhile, speech
path from PSTN to Your device shall not be honured by your service provider.
 
Best Regards,
Vivek Batra 

  _____  

From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of Ranjith Kumar
Sent: Thursday, July 23, 2009 2:33 PM
To: discussion at sipforum.org
Subject: [SIPForum-discussion] One Way speech During the Initial Few seconds


Hi All,
 
I am trying to connect a Sip trunk to a PBX.  When i try to make a outgoing
call from the PBX subscriber to a PSTN user I have one way Speech for the
initial few seconds.  I tried to capture the traces but I was unable to find
the actual rootcause.  Please let me know if I am missing out something.
 
PBX 10.0.32.2 
Provider : 195.146.137.250
 
I attach the traces here.
 
regards,
 



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