HMR to manipulate 503 received from INVITE to a 4xx message whilst preserving OPTIONS 503
We've an issue with our SIP trunk session agents being knocked out of service in response to receiving a 503 Service Unavailable message for an INVITE for an outbound call, since our SIP trunk provider is just passing through this message received from outside of their network.
503 is the only entry that we have in the out-service-response-codes of our trunk session agents.
My thought was to author a HMR that could be applied on the trunk realm's in-manipulationid - we already have an out-manipulationid HMR used to hide IP topology - that would
1) Change a 503 received in response to an INVITE to a 4xx message e.g. 404 Not Found