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Third-Party Cloud Client Does Not Hear the Ringback Tone After Placing a Call

Publication Date:  2019-04-04 Views:  12 Downloads:  0
Issue Description

Software versions: U1981 V200R003C30SPC500B011, U1960 V200R003C30SPC500B011, Huawei eSpace 7950 V200R003C00

Topology: Third-party cloud client -> Cloud server -> SIP proxy -> 1981 -> U1960 -> PRA

Problem description: A third-party cloud client does not hear the ringback tone (RBT) when calling an intra-office or inter-office PSTN user.

Handling Process

There are two scenarios for this problem, that is, intra-office and inter-office PSTN calls.

1. According to the captured packets, when a call is made to an intra-office phone, the phone returns a 180 message, and the PBX forwards the 180 message to the calling party.

2. According to the captured packets, when a call is made to an inter-office PSTN user, the peer end returns a 183 message.

Root Cause

The calling party does not hear the ringback tone if the third-party device does not support the following mechanism used by the U19 to reply a 18x message.

1. When A calls B, B returns a 180 message without a media message. In this case, A's device plays the RBT.

2. When A calls B, B returns a 183 message with a media message. In this case, the system considers that color ring back tone (CRBT) is enabled and instructs B's device to play the RBT to A.


1. Calling an inter-office user

a) If the remote end is an IMS SIP network, enable software parameter 307. If there are other SIP trunks, you are advised not to enable this software parameter.

Command: config softargu type 307 value 0/1

b) If the PSTN side returns a 183 message and no RBT is played, check whether the PSTN side supports the CRBT service (as the U19 only forwards the call).

c) If it is a PBX on the cloud side, currently the U19 only forwards the call. You can change the value of software parameter 270 to determine whether to hear an announcement of the reason for call forwarding.

2. Calling an intra-office user

A 180 message indicates that the calling device needs to play the RBT. The third party needs to check whether its product supports the playing of RBT. If not, the third party needs to purchase the CRBT server and perform the following configurations:

(1) Configure the SIP trunk for connecting to the CRBT server.

(2) Configure the external CRBT server.

a. Set the following parameters on the account page:

b. On the U19 POTS user interface, modify calling number services to enable the CRBT service.