In my last post, you read about SIP call recovery from RTP loss. This post continues the theme, providing some more useful information – detecting and dealing with RTP loss between two SIP end points.
If you recall the scenario, there is a gateway installed between an SS7 carrier network and an emergency services IP network – an ESInet – over which emergency calls are routed to public safety answering points (PSAPs). Calls entering the ESInet via the gateway are SIP/RTP/UDP and, as the NENA i3 specification quite rightly states, in no circumstances should an in-progress emergency call be taken down automatically, just because RTP streams fail.
Whatever effort you put into making the call handling equipment redundant and resilient, it is always best to assume that bad things can still happen. To misappropriate the principle of simplicity from Ockham’s razor, follow the rule of thumb that advises, “Make as few assumptions as possible.” In fact, make one assumption only – expect the worst (i.e., ‘the proverbial’ happens).
So, we can expect situations to arise in which RTP media between the gateway and the ESInet fails.
PSAP equipment must be able to distinguish between RTP failure and real silence by a caller. Continue Reading...
If you recall the scenario, there is a gateway installed between an SS7 carrier network and an emergency services IP network – an ESInet – over which emergency calls are routed to public safety answering points (PSAPs). Calls entering the ESInet via the gateway are SIP/RTP/UDP and, as the NENA i3 specification quite rightly states, in no circumstances should an in-progress emergency call be taken down automatically, just because RTP streams fail.
Whatever effort you put into making the call handling equipment redundant and resilient, it is always best to assume that bad things can still happen. To misappropriate the principle of simplicity from Ockham’s razor, follow the rule of thumb that advises, “Make as few assumptions as possible.” In fact, make one assumption only – expect the worst (i.e., ‘the proverbial’ happens).
So, we can expect situations to arise in which RTP media between the gateway and the ESInet fails.
PSAP equipment must be able to distinguish between RTP failure and real silence by a caller. Continue Reading...
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