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This document describes the H.323 Call Redirection Enhancements feature that was introduced in Cisco IOS Release 12.2(1)T. This document contains the following sections:
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.
There are two situations in which the Cisco H.323 Gateway might receive or generate a facility message with a routeCallToGatekeeper reason.
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 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 E164 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 and 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.
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 will place the call on hold and initiate 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 E164 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 and 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.
Unlike in call forwarding case, the Facility message is accepted by both the called side and the originating side.
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Note This use of call forwarded is not defined by ITU standard. |
The H.323 Call Redirection Enhancements feature allows for more robust handling of call transfers and redirections.
The H.323 Call Redirection Enhancements feature has the following restrictions and limitations:
The H.323 Call Redirection Enhancements feature is related to the H.323 VoIP Gateway for Cisco Access Platforms feature.
The H.323 Call Redirection Enhancements feature is supported on any existing IOS gateway platforms, including the following:
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO.
RFCs
No new or modified RFCs are supported by this feature.
The H.323 Call Redirection Enhancements feature requires the Cisco H.323 VoIP Gateway for Cisco Access Platforms feature.
There are no configuration tasks for the H.323 Call Redirection Enhancements.
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Note 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. |
Because there are no configuration tasks, no configuration examples are provided.
ACF—RAS message sent as an admission confirmation.
ARJ—RAS message sent as an admission rejection.
ARQ—RAS message sent as an admission request.
DCF—RAS message sent as a disengage confirmation.
DRQ—RAS message sent as a disengage request.
gatekeeper—A gatekeeper maintains a registry of devices in the multimedia network. The devices register with the gatekeeper at startup, and request admission to a call from the gatekeeper.
The gatekeeper is an H.323 entity that provides address translation and control access to the network for H.323 terminals and gateways. The gatekeeper may provide other services to the H.323 terminals and gateways, such as bandwidth management and locating gateways.
gateway—A gateway allows H.323 terminals to communicate with non-H.323 terminals by converting protocols. A gateway is the point at which a circuit-switched call is encoded and repackaged into IP packets.
A H.323 gateway is an endpoint that provides real-time, two-way communications between H.323 terminals on the network and other ITU-T terminals in the WAN, or to another H.323 gateway.
H.323—An International Telecommunication Union (ITU-T) standard that describes packet-based video, audio, and data conferencing. H.323 is an umbrella standard that describes the architecture of the conferencing system, and refers to a set of other standards (H.245, H.225.0, and Q.931) to describe its actual protocol.
POTS—Plain old telephone service. Basic telephone service supplying standard single line telephones, telephone lines, and access to the PSTN.
PSTN—Public switched telephone network. PSTN refers to the local telephone company.
RAS—Registration, admission, and status protocol. This is the protocol that is used between endpoints and the gatekeeper to perform management functions. The RAS signaling function performs registration, admissions, bandwidth changes, status, and disengage procedures between the VoIP gateway and the gatekeeper.
VoIP—Voice over IP. The ability to carry normal telephone-style voice over an IP-based Internet with POTS-like functionality, reliability, and voice quality. VoIP is a blanket term which generally refers to Cisco's standards-based (H.323, etc.) approach to IP voice traffic.
Posted: Wed Sep 6 06:11:21 PDT 2000
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