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One-Way Audio Occurs to the GPON VoIP (SIP) Service Due to the Customer’s Softswitch Problem

Publication Date:  2012-07-25 Views:  58 Downloads:  0
Issue Description
Symptom:
In the early test on an overseas commercial office, both parties can hear each other after the PSTN initiates a call to the ONT; after the ONT initiates a call to the PSTN, the ONT cannot hear the PSTN while the PSTN can hear the ONT.
Networking:
HG850?MA5680T?Cisco 6509?BRAS E320?Siemens softswitch HIE9200 v S5?UMG?PBX?PSTN phone
Version:
OLT: MA5680T MA5600V800R005C32B136 + SPH001 + HP1004
ONT: HG850 HG850-V100R001C01B031-all 
 
Alarm Information
Null
Handling Process
Submit the preceding analysis to the customer for discussion. After the RTP packetization time on the softswitch is adjusted, this problem is solved satisfactorily.  
Root Cause
1. Analyze the packets generated when the ONT calls the PSTN:
Firstly, the packetization time in the packet the ONT sends to the softswitch is 20 ms, but the 200 OK response of the softswitch contains no packetization time.
Secondly, lots of RTP packets are sent by the softswitch nearly at the same time. Our RTP packets are normal. One RTP packet is received at an interval of 20 ms.
2. Analyze the packets generated when the PSTN calls the ONT normally.
Firstly, the INVITE packet the softswitch sends contains no packetization time, the 200 OK response of the ONT contains the packetization time.
Secondly, check the RTP packets: The RTP packet the softswitch sends to the ONT contains the packetization time of 20 ms, and the RTP packet the ONT sends to the softswitch contains the packetization time of 20 ms. Therefore, both parties can hear each other.
3. Conclusion:
To sum up, the RTP packetization on the customer’s softswitch is not normal, so the ONT cannot hear the PSTN.
For details on the location procedure (including the screen capture) and data configuration, see the attachment. 
 
Suggestions
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