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.