FW: Where H.245 goes - MG or MGC

Tom-PT Taylor taylor at NORTELNETWORKS.COM
Mon Mar 8 13:07:06 EST 1999

> -----Original Message-----
> From: David R. Oran [SMTP:oran at 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?

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