Clearwater allows users to define rules for handling of incoming calls, by implementing a superset of the IR.92 version of call diversion (which is itself a cut-down version of the MMTEL call diversion service).
The relevant specifications are
We have implemented all of IR.92 section 2.3.8. We have implemented all of 3GPP TS 24.604 with the following exceptions.
- CDIV Notification (notifying the diverting party when a call has been diverted) is not supported
- We only support the default subscription options from table 22.214.171.124 (most notably, no privacy options).
- We only support hard-coded values for network provider options from
table 126.96.36.199, as follows.
- We stop ringing the diverting party before/simultaneously with
trying the diverted-to target (rather than waiting for them to
- Served user communication retention on invocation of diversion (forwarding or deflection) = Clear communication to the served user on invocation of call diversion
- Served user communication retention when diverting is rejected at diverted-to user = No action at the diverting user
- We don’t support CDIV Notification (as above).
- Subscription option is provided for “served user received reminder indication on outgoing communication that CDIV is currently activated” = No
- CDIV Indication Timer = irrelevant
- CDIVN Buffer Timer = irrelevant
- We support up to 5 diversions and then reject the call.
- Total number of call diversions for each communication = 5
- AS behavior when the maximum number of diversions for a communication is reached = Reject the communication
- The default no-reply timer before Communication Forwarding on no
Reply occurs is hard-coded to 20s. This is still overridable on a
- Communication forwarding on no reply timer = 36s
- We stop ringing the diverting party before/simultaneously with trying the diverted-to target (rather than waiting for them to start ringing).
- Obviously, the interactions with services that we haven’t implemented yet have not been implemented! In particular, we haven’t implemented any interactions with terminating privacy.
- We’ve ignored the comment in section 188.8.131.52 which says “It should be possible that a user has the option to restrict receiving communications that are forwarded” but doesn’t provide any function for this.
Note that we have implemented support for Communication Deflection (in which the callee sends a 302 response and this triggers forwarding) despite it not being required by IR.92.