H.225 v4 contains this text: "7.11.2 AdmissionConfirm (ACF) ... alternateEndpoints - A sequence of prioritized endpoint alternatives for destCallSignalAddress or destinationInfo."
The feature seems intended to support robustness through redundancy in large networks, where there may be more than one media gateway capable of serving the same AdmissionRequest (ARQ). This would accord with the support for alternate gatekeepers in H.323 v4: "7.2.6 Alternate gatekeeper procedures For the purposes of ensuring system availability, redundancy, and scalability, the Gatekeeper may provide the RAS signalling function by utilizing multiple physical or logical devices, referred to as Alternate Gatekeepers. If the endpoint supports the Alternate Gatekeeper procedures defined in this section, it should include the supportsAltGK field in the GRQ and RRQ messages. When an endpoint initiates communication with the Gatekeeper, it may be provided with a list of Alternate Gatekeepers via the GCF message. If the Gatekeeper does not respond to the subsequent RRQ, the endpoint shall attempt to register with the Gatekeeper using the list of Alternate Gatekeepers provided in the GCF. If no Alternate Gatekeeper responds, the endpoint shall reinitiate the Gatekeeper discovery process."
The problem is that there are no procedures specified for the use of alternateEndpoints. What is it that causes a caller to terminate its Setup attempt to one destination and to initiate a Setup attempt to the next destination in priority order?
Can we presume that the critical event is receiving a ReleaseComplete? Then how do we determine whether the release reason or cause code is final (no further Setup should be sent) or not (try another destination)? Some calls should end after an announcement is played, eg. "The number you are calling has been disconnected", and will never succeed no matter how many alternative endpoints are attempted.
If the intention of alternateEndpoints has already been clarified somewhere, please point me to it and excuse my ignorance.
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