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In this section:
The SBC Core 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 SBC 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.
set profiles signaling signalingProfile <profile name> egress egressFlags callBackWhenFreeSupport <disable | enable>
The SBC, Ribbon GSX and ASX support CBWF for the following protocol interworkings (see call flow diagram):
Figure 1: SIP Protocol Interworking Using CBWF
CBWF is implemented on the SBC 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. |
The SBC Core also supports following configurations:
CLI command syntax:
set profiles signaling isupSignalingProfile <profile name> sendAPPinAPMforCBWF <supported | unsupported> set profiles signaling isupSignalingProfile <profile_name> sendPRIonRELforCBWF <supported | unsupported>
If the SBC 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 SBC releases the call.
This functionality takes precedence over the ISUP Signaling Profile flag transitCfn
used to transit the CONFUSION message towards the other leg.