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Mobile phone cannot hear ringing back tone when make a call to eSpace U1980 through R2 trunk

Publication Date:  2014-06-25 Views:  121 Downloads:  0
Issue Description
One customer have eSpace U1980 device with V100R001C01SPC800 version, which interconnected PSTN with R2 trunk, when they make a incoming calls from a Mobile phone, they cannot hear the ringing back tone, but the call can be established without problems. 
Alarm Information
Handling Process
1. Capture call logs of U1980
2. Check the log, and found that the call was established after U1980 send A6 message.

3. Modify the R2 trunk configuration to enable group B signaling., the command is: "config modify cassignal casname xxx needbgroupsignal yes"
4. Then test incoming call again, the Mobile phone can hear the ringing back tone, the issue is resolved.
Root Cause
R2 trunk in different country have different configuration,  need to use different script and parameters , in this case, it was due to the default R2 trunk configuration are using group A, but not using group B, this cause the PSTN cannot recognize this signaling, and no ringing back tone. 
Before interconnection with R2 trunk, need to understand the R2 parameter in peer side, such as the type of register singling, the type of line singling, if use B group singling etc.