osmo-mgw: Implement MGCP RestartInProgress (RSIP)
We could delay exit() of the osmo-mgw process during SIGINT, to transmit RestartInProgress to all active endpoints, so that the call agent (bsc, msc, etc.) knows it has to terminate the calls.
This could perhaps even be used by Call agent to keep calls working by signalling peer BSC/BTS/MSC/etc. to change to another MGW if there's an MGW pool with more available MGW, providing higher reliability?
This could also be used to signal disconnect or temporary unavailability to E1 timeslots, etc.
* The Gateway can use the RestartInProgress command to notify the Call Agent that a group of endpoints managed by the gateway is being taken out-of-service or is being placed back in-service.
2.3.12 RestartInProgress The RestartInProgress command is used by the gateway to signal that an endpoint, or a group of endpoints, is put in-service or out-of- service.
Gateways SHOULD send a "graceful" or "forced" RestartInProgress message (for the relevant endpoints) as a courtesy to the Call Agent when they are taken out-of-service, e.g., by being shutdown, or taken out-of-service by a network management system, however the Call Agent cannot rely on always receiving such a message. Gateways MUST send a "restart" RestartInProgress message (for the relevant endpoints) with a null delay to their Call Agent when they are back in-service according to the restart procedure specified in Section 4.4.6 - Call Agents can rely on receiving this message. Also, gateways MUST send a "disconnected" RestartInProgress message (for the relevant endpoints) to their current "notified entity" according to the "disconnected" procedure specified in Section 4.4.7. The RestartInProgress message will be sent to the current "notified entity" for the EndpointId in question. It is expected that a default Call Agent, i.e., "notified entity", has been provisioned so that after a reboot/restart, the default Call Agent will always be the "notified entity" for the endpoint. Gateways SHOULD take full advantage of wild-carding to minimize the number of RestartInProgress messages generated when multiple endpoints in a gateway restart and the endpoints are managed by the same Call Agent.
8) RestartInProgress MUST always be the first command sent by an endpoint as defined by the restart procedure. Any other command or non-restart response (see Section 4.4.6), except for responses to auditing, MUST be delivered after this RestartInProgress command (piggybacking allowed).
In some cases, many gateways may decide to restart operation at the same time. This may occur, for example, if an area loses power or transmission capability during an earthquake or an ice storm. When power and transmission are reestablished, many gateways may decide to send "RestartInProgress" commands simultaneously, leading to very unstable operation.
A virtual endpoint may be created as the result of using the "any of" wildcard. Similarly, a virtual endpoint may cease to exist once the last connection on the virtual endpoint is deleted. The definition of the virtual endpoint MUST detail both of these aspects. When a <virtual-endpoint-type> creates and deletes virtual endpoints automatically, there will be cases where no virtual endpoints exist at the time a RestartInProgress command is to be issued. In such cases, the gateway SHOULD simply use the "all of" wildcard in lieu of any specific <endpoint-#> as in, e.g.: email@example.com If the RestartInProgress command refers to all endpoints in the gateway (virtual or not), the <virtual-endpoint-id> can be omitted as in, e.g.: *@mygateway.whatever.net
It seems we must also be sending that message for each available endpoint at startup AFAIU (or 1 with wildcard "*"). We seem to be missing a "default Call Agent" in osmo-mgw though":
It is expected that a default Call Agent, i.e., "notified entity", has been provisioned so that after a reboot/restart, the default Call Agent will always be the "notified entity" for the endpoint. .... Note that as mentioned earlier, the default "notified entity" is provisioned and may include both domain name and port. For small gateways, provisioning may be done on a per endpoint basis. For much larger gateways, a single provisioning element may be provided for multiple endpoints or even for the entire gateway itself. In either case, once the gateway powers up, each endpoint MUST have its own "notified entity", so provisioned values for an aggregation of endpoints MUST be copied to the "notified entity" for each endpoint in the aggregation before operation proceeds. Where possible, the RestartInProgress command on restart SHOULD be sent to the provisioned "notified entity" based on an aggregation that allows the "all of" wild-card to be used. This will reduce the number of RestartInProgress messages.