H.323 Call Redirection Enhancements


Release	Modification
12.1(5)XM	This feature was introduced.
12.2(1)T	This feature was integrated into Cisco IOS Release 12.2(1)T.
12.2(2)XB1	This feature was implemented on the Cisco AS5850 platform.
12.2(11)T	This feature was integrated into Cisco IOS Release 12.2(11)T.

This document describes the H.323 Call Redirection Enhancements feature. This document includes the following sections:

Feature Overview

The user-to-user information element (UUIE) of the facility message is used primarily for call redirection. The UUIE contains a field, facilityReason, that indicates the nature of the redirection. The H.323 Call Redirection Enhancements feature adds support for two of the reasons: routeCallToGatekeeper and callForwarded. It also provides a non-standard method for using the facility message to effect call transfer.

Route Call to Gatekeeper

The following are situations in which the Cisco H.323 gateway might receive or generate a facility message with a routeCallToGatekeeper reason:

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The gateway receives a facility message with routeCallToGatekeeper as a response to its H.225 setup message. Upon receiving the facility message, the Cisco H.323 gateway attempts to route the call to the new Gatekeeper, using the new IP address specified in the alternativeAddress field of the facility message.

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If the IP address is not available, the gateway ignores the facility message and sends a release complete toward the original destination endpoint. The release complete message contains a ReleaseCompleteReason of facilityCallDeflection.

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If the IP address is available, the gateway sends a disengage request (DRQ) message to the Gatekeeper and waits for the disengage confirmation (DCF) message before it sends the setup message to the new destination Gatekeeper.

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During the admission request (ARQ) phase of a call, a Gatekeeper might determine that a call, which has come through an intermediate gateway, needs to be routed to another Gatekeeper.

The Gatekeeper sends an admission rejection (ARJ) message with a RejectReason of routeCallToGatekeeper to the gateway.

Upon receiving the message, the intermediate Cisco H.323 gateway sends a facility message to the originator of the setup message. This message indicates that the setup message should be sent to another address. (The gateway includes the callSignalAddress from ARJ in the alternativeAddresss field of the facility message.)

Upon receiving the facility message, the calling gateway terminates the initial call and sends a new setup message to the specified Gatekeeper, using the new IP address specified in the alternativeAddress field of the facility message. If the callSignalAddress is not provided, the gateway does not send the facility message and the call is terminated without any rerouting.

Call Forward

In certain cases, an H.323 endpoint might determine that a call needs to be forwarded. The endpoint then sends a facility message to the gateway with a facilityReason of callForwarded. This message includes the address of the new destination (either an alternativeAddress or alternativeAliasAddress). Upon receiving the facility message, the Cisco H.323 gateway sends a release complete message to the original destination endpoint and initiates a new call using the new destination address supplied in the facility message. The release complete message contains a ReleaseCompleteReason of facilityCallDeflection. If the gateway is registered with a Gatekeeper, the gateway sends a DRQ to the Gatekeeper and waits for the DCF before sending a setup message to the destination Gatekeeper.

The facility message must contain an E.164 address in the alternativeAliasAddress field. If no address is included, the facility message is ignored. The E.164 message is required because the call forwarding process initiates a new call, which may be subject to authentication processes that can handle only E.164 addresses.

If the facility message contains both an IP address (in the alternativeAddress field) and an E.164 address (in the alternativeAliasAddress field), the gateway first attempts to find a match for the new E.164 address and the dial-peer. If there is no match, the gateway uses the same incoming peer to determine if there is a matching peer to reroute the call. If there is no match to the incoming peer, the message is ignored.

Call Transfer

If a facility message with a facilityReason of callForwarded is received after the call has been accepted, it is considered a call transfer. In this case, the Cisco H.323 gateway places the call on hold and initiates a new call using the address (alternativeAddress or alternativeAliasAddress) supplied in the facility message.

As with call forwarding, the facility message must contain an E.164 address in the alternativeAliasAddress field. If no address is included, the facility message is ignored. The E.164 address is required because the call transfer process initiates a new call, which may be subject to authentication processes that can handle only E.164 addresses.

If the facility message contains both an IP address (in the alternativeAddress field) and an E.164 address (in the alternativeAliasAddress field), the gateway first attempts to find a match for the new E.164 and the dial-peer. If there is no match, the gateway uses the same incoming peer to determine if there is a matching peer to reroute the call. If there is no match to the incoming peer, the message is ignored.

In contrast with the call forwarding case, the facility message is accepted by both the called side and the originating side.

Benefits

The H.323 Call Redirection Enhancements feature allows for more robust handling of call transfers and redirections.

Restrictions

The H.323 Call Redirection Enhancements feature has the following restrictions and limitations:

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The application command must specify the session application for the dial peers.

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The H.323 Call Redirection Enhancements feature does not provide the ability for a Cisco H.323 gateway to initiate a call transfer request.

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If you configure static Gatekeepers from the command line interface (CLI), they will still be inserted into the alternate Gatekeeper list during the admission confirmation (ACF) phase.

Related Features and Technologies

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