When the IMS-ALG requires that an IMS-AGW congestion notification mechanism be applied in the MGW, the IMS-ALG shall use the IMS-AGW Resource Congestion Handling - Activate procedure towards the IMS-AGW.
When the IMS-ALG receives a load reduction notification from the IMS-AGW via the IMS-AGW Resource Congestion Handling - Indication procedure, the IMS-ALG tries to reduce the processing load that the IMS-ALG creates on the IMS-AGW. The IMS-AGW shall decide the actual level of traffic reduction.
Monitoring of the H.248 control association may be performed by monitoring the status of the transport link association where the transport protocol provides sufficient coupling to the H.248.1 protocol, i.e. if the transport link association is disconnected when no local H.248.1 protocol connection exists.
An alternative method for the IMS-AGW to detect loss of the IMS-ALG may be achieved by requesting the IMS-AGW to poll the IMS-ALG periodically
Upon registration of an IMS-AGW, the IMS-ALG may use the Inactivity Timeout - Activate procedure towards the IMS-AGW to request the IMS-AGW to monitor incoming messages for periods of silence exceeding the maximum inactivity timer value.
Upon receipt of an inactivity timeout notification from the IMS-AGW via the Inactivity Timeout - Indication procedure, the IMS-ALG shall send a reply to the IMS-AGW. If the IMS-ALG has failed, the IMS-AGW will not receive a reply.
If no Inactivity Timeout - Indication Ack reply is received, the IMS-AGW shall consider the IMS-ALG to have failed. The IMS-AGW may then attempt to re-contact its controlling IMS-ALG by performing IMS-AGW Communication Up. If not successful, the IMS-AGW may then attempt to register to a new IMS-ALG.
If the IMS-AGW supports IP Realm Availability monitoring, the IMS-ALG may request the monitoring of the available IP Realms by the IMS-AGW; the IMS-AGW shall inform the IMS-ALG of any changes in realm availability.
The IMS-ALG may use the Realm Availability - Activate procedure towards the IMS-AGW to request the IMS-AGW to monitor the status of its IP Realms.
This procedure only applies when text encoding is used on the H.248 interface.
The IMS-ALG shall and the IMS-AGW may support the Termination Out-of-Service procedure.
If the IMS AGW suffers a loss of physical IP device(s) that pertain to a whole IP Realm it may report the IP Realm as unavailable (see clause 6.1.14). However, it is possible that a failure affects a physical port or group of ports that forms a subset of the IP Realm and therefore many terminations are affected. In such cases the IMS-AGW may initiate a Termination Out of Service procedure to inform the IMS-ALG that the set of terminations is out of service. This is shown in Figure 6.1.15.1.
On receipt of the Termination Out Of Service the IMS-ALG shall initiate the appropriate actions, e.g. by subtracting the affected terminations and releasing the affected calls.