Doug- Check section B of the H.248 spec for one example of the use of dynamic payload type - it's used to indicate where in the media stream the encryption mechanism/key changed. I'd venture that this technique should be used more generally to indicate any discontinuity in the media stream (e.g., due to redirection) when the codec in use didn't actually change. -Bob ---------------------------------------------------- Bob Gilman rrg@avaya.com +1 303 538 3868

Douglas Clowes wrote:

Could some kind soul please point me to the definitive guide to the use of RTP dynamic payload types in H.245. I've looked and can't seem to find any adequate coverage.

If anybody has firm ideas how it's done, I would be pleased to receive the benefit of their knowledge.

The documentation talks about the use of dynamic payload types in the use of alternative packetisation for video, but there seems to be a need for dynamic payload types in audio codecs which have H.245 code points, but not RTP static payload types (such as GSM HR and EFR).

Dynamic payload types are being used for mode specification in SDP as well, with some MGs using them to specify the desired rate for G.723.1 (High or Low).

IMHO, the standard needs to be expanded on the use of dynamic paylaod types, with particular reference to interworking with SDP based MGs and SIP.

Cheers,

Douglas Clowes

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