Ringback Tone Is Heard When a C&C08 User Makes an Intra-Office Call to an eSpace U1980 User Who Is Busy

Publication Date:  2015-07-24 Views:  329 Downloads:  0
Issue Description
In one office, two eSpace U1980s are deployed as the trunk gateway and voice gateway respectively. They are connected through a SIP trunk. The trunk gateway connects to China Unicom PSTN through a PRI trunk. The trunk gateway and the existing C&C08 stored program control exchange (SPC) are connected through a PRI trunk. The following figure shows the network.



Based on the data configuration, IP phones connected to the eSpace U1980 voice gateway can make calls with analog phones connected to the C&C08 SPC, and can make incoming and outgoing local or toll calls.

When an outer-office PSTN phone or intra-office IP phone connected to the eSpace U1980 voice gateway makes a call to another intra-office IP phone that is busy, an announcement is played, indicating that the called party is busy.

However, when an analog phone connected to the C&C08 SPC makes a call to an intra-office IP phone under the U1980 that is busy, the calling party hears the ringback tone instead of the announcement indicating that the called party is busy. The customer thinks that this is improper because analog phone users on the C&C08 SPC may consider that the called party intentionally ignores the call.
Handling Process
Contact C&C08 engineers to modify the announcement playback parameter to allow the eSpace U1980 to play the announcement. After that, when an analog phone connected to the C&C08 SPC makes a call to an intra-office IP phone that is busy, the calling party can hear the announcement indicating that the called party is busy.
Root Cause
In this office, the eSpace U1980 trunk gateway connects to the intra-office C&C08 SPC through PRA signaling on a digital E1 trunk. Based on the analysis of signaling and logs captured when an analog phone connected to the C&C08 SPC makes a call to an intra-office IP phone that is busy, the eSpace U1980 plays an announcement to the calling party and uses the progress indicator information unit in the ALERT message of PRA signaling to notify the C&C08 SPC that the called party will play an announcement.

Based on the Q931 protocol for PRA signaling, a device can choose to hear the announcement played by the peer device or play an announcement by itself when the device detects the progress indicator information unit in the ALERT message and the progress indicator value is 8 (In-band information or an appropriate pattern is now available).

When the C&C08 SPC detects the progress indicator information unit in the ALERT message sent by the eSpace U1980 trunk gateway and the progress indicator value is 8, the C&C08 SPC chooses to play an announcement by itself.

It is recommended that the peer device (that is, the eSpace U1980) play the announcement.
Suggestions
When delivering an IP telephony (IPT) project, ensure that test cases are sufficient. The test cases verify proper basic call functions as well as correctly played announcements to prevent user confusion.

When finding that a fault is not caused by eSpace U19xx gateways, contact the customer in a timely manner and prompt third-party device vendors or maintenance parties to rectify the fault.

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