Overview
The
supports Call Back When Free (CBWF) feature, also known as Ring Back When Free (RBWF), for UK-ISUP, IUP, SIP-I and SIP interworkings. When the
is configured for CBWF support (
callBackWhenFreeSupport flag
), a call is automatically established to a destination number that was previously busy without the need for the calling party to redial the number.
| Code Block |
|---|
|
set profiles signaling signalingProfile <profile name> egress egressFlags callBackWhenFreeSupport <disable | enable>
|
The
, Ribbon GSX and ASX support CBWF for the following protocol interworkings (see call flow diagram):
- SIP-I (UK-ISUP) to BT-IUP interworking over GW with Ribbon GSX.
- SIP to SIP-I (UK-ISUP) interworking
- SIP-I (UK-ISUP) to SIP-I(UK-ISUP) interworking
- SIP to BT-IUP (supported on GSX only)
Figure 1: SIP Protocol Interworking Using CBWF
CBWF is implemented on the
using four separate but related signaling sequences described in the table below.
Table 1: CBWF Signaling Sequences
| Signaling Sequences | Usage |
|---|
| Call Back When Free - Request | Calling party requests the registration of CBWF at the Originating and Terminating PBXs. |
Call Back When Free - Free Notification | Notifies the originating network about the status of the called party. |
| Call Back When Free - Call Set-Up | Establishes call between the requesting and desired extensions. This follows the receipt of a Free Notification when the extension is/becomes free. |
Call Back When Free - Cancel Request | The calling party cancels the call, or when a CBWF Request is canceled as the result of a timeout. |
Additional CBWF Configurations
The
also supports following configurations:
- Sending CBWF-related APP (ACI=126) in a new APM (Application Transport Message)
- Sending PRI/APM message during tear down of CBWF call for SIP-to-SIP-I interworking scenario.
CLI command syntax:
| Code Block |
|---|
|
set profiles signaling isupSignalingProfile <profile name> sendAPPinAPMforCBWF <supported | unsupported>
set profiles signaling isupSignalingProfile <profile_name> sendPRIonRELforCBWF <supported | unsupported> |
| Note |
|---|
If the is configured for CBWF and if a CONFUSION message contains Cause 99 or Cause 110 indicating an error in the APP parameter is received on the SIP-I leg, the releases the call.This functionality takes precedence over the ISUP Signaling Profile flag transitCfn used to transit the CONFUSION message towards the other leg. |