-----Original Message----- From: David R. Oran [SMTP:oran@cisco.com] Sent: Monday, March 08, 1999 10:25 AM To: megaco Subject: Where H.245 goes - MG or MGC
Here are some random thoughts on one of the questions of marrying Megaco with H.323 - where H.245 goes. Some prior messages have indicated that there are tradeoffs involved here, and I agree. Some food for thought:
- If we terminate H.245 on the MG, this blows away V2 fast start, and
looking at likely call flows may introduce 1/2 RTT extra over a monolothic H.323 gateway.
The MGC may wish to participate in CAPs exchange for policy reasons.
The H.245 open logical channel operation is analogous to doing VC
establishment on the MG in the ATM case, and for parallelism might be best done MG-MG. It is also where certain resource allocation operations get done and hence synchronizes well with the H.323 model of error reporting. Unfortunately, putting CAPs excahnge in one association and logical channel control in a different association would be a pretty major tweak to H.323.
- Putting H.245 completely on the MG factors the problem of translating
among different media description syntaxes (e.g. H245/ASN1 vs SDP) - the MGC-MG protocol then might not need to have a full-blown media description in it when using H.323 for global signaling.
- Putting H.245 on the MG gives the MG a lot of autonomy. This is arguably
more autonomy than the Megaco model should assign to the MG.
- Splitting up H.323 with H.225 signaling in one place and H.245 signaling
in another place may uncover some state coordination issues which would (unneccesarily?) complicate the MGC-MG protocol and possibly introduce direct H.323 dependencies.
My intuition says that the tradeoffs favor keeping H.245 in the MGC. What do others think?