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In the Virtual Group, Calls from Phones Attached to the MA5620 Cannot Be Connected to Phones Attached to the MDU of Z Company Because Compression Algorithm on the Softswitch is Mismatched

Publication Date:  2012-07-25 Views:  47 Downloads:  0
Issue Description
Network structure
5620E?MA 5680T?Softswitch of Z Company?OLT of Z Company?MDU of Z Company
After the phones attached to the 5620E and the phones attached to the MDU of Z Company are added to the same virtual group, the phones of Z Company can call the phones attached to the 5620E normally. If a phone attached to the 5620E calls a phone attached to the MDU of Z Company, a busy tone is heard and the call fails. The IP address of the MG interface of the 5620E is 10.15.65.252, the IP address of the MG interface of Z Company is 10.15.65.251, and the IP address of the softswitch of Z is 10.15.4.2.
The version of the 5620E is V800R305C01B026, with the SHP001 and HP0003 patches loaded. 
 
Alarm Information
Null
Handling Process
1. On the 5620E, mirror the upstream PON port through the Ethernet port to capture signaling, and call a phone attached to the 5620E by using a phone attached to the MDU of Z Company. The result is as follows:
11939 20.052329 10.15.4.2 10.15.65.252 MEGACO/SDP 1910539748 Request |=18 Modify=R100000018
c=IN IP4 10.15.65.251
m=audio 4058 RTP/AVP 8
//In the signaling sent by the softswitch of Z, the A-law compression algorithm is used first. In the signaling, the parameter value is 8.
11972 20.085945 10.15.65.252 10.15.4.2 MEGACO/SDP/SDP 1910539748 Reply |=18 Modify=R100000018,
c=IN IP4 10.15.65.252
m=audio 49520 RTP/AVP 8
//The Huawei 5620E can respond to the softswitch by using the A law. The negotiated parameters of two parties are consistent, and the call between two parties is normal.
2. Call a phone attached to the MDU of Z Company by using a phone attached to the 5620E to capture signaling. The result is as follows:
187 4.769571 10.15.4.2 10.15.65.252 MEGACO/SDP 1910540397 Request |=Choose one Add Add=$ (Mode:RC)
m=audio $ RTP/AVP 0 8
//The Huawei 5620E initiates a call. In the signaling sent by the softswitch of Z Company, the compression algorithm contains both the A law and μ law. The parameter of the μ law is 0.
191 4.810349 10.15.65.252 10.15.4.2 MEGACO/SDP 1910540397 Reply |=22 Add Add=R100000020 (Mode:RC)
m=audio 49512 RTP/AVP 0
//The Huawei 5620E responds to the softswitch by using the μ law.
193 4.820967 10.15.4.2 10.15.65.252 MEGACO 1910540398 Request |=22 Modify (Signal:{)
SG{
cg/bt}}}}
//After the Huawei 5620E makes a response, the softswitch sends a busy tone directly. The call fails.
3. Ask the customer to modify the softswitch parameter of Z Company through the NMS: Modify “original m=audio $ RTP/AVP 0 8” to “m=audio $ RTP/AVP 8” in the SDP description, and force the use of the A law only. Now, two parties can call each other normally. 
 
Root Cause
1. The signaling of Z’s softswitch contains private contents, so the negotiation of voice parameters fails.
2. Due to the fault of Huawei’s 5620E, the parameter negotiation between the 5620E and Z Company’s softswitch fails. 
 
Suggestions
1. Facing a problem concerning the interconnection with the device of a competitor, engineers can handle the problem by tracing signaling and analyzing the captured packets from the media stream.
2. The compression algorithm in the softswitch of Z Company contains both A law and μ law, but the Huawei 5620E uses the μ law to negotiate with the parameter. The negotiation fails. Therefore, the use of the A-law compression algorithm is forced for the softswitch of Z Company. 
 

END