SIP beats H323?

Lyons, Terry TLyons at SONUSNET.COM
Fri Oct 31 14:05:16 EST 2003


Thanks for the pointers.  I shall look for a new generic capability
in the next edition of H.245.

H.323 devices negotiate to optimize voice quality.  If it is likely
that the receiver will discard CN packets, a transmitter may achieve
better results by sending G.711 without interruption.

- tlyons at +1 732 625-3003 x212

-----Original Message-----
From: Paul Long [mailto:plong at PACKETIZER.COM]
Sent: Friday, October 31, 2003 1:08 PM
To: itu-sg16 at
Subject: RE: SIP beats H323?


First of all, RFC 3389 specifies its use with SDP, not SIP, per se. SDP is
used by several protocols, one of which is SIP. Maybe your subject hedaer
should have been "SDP beats H245?" :-)

While it is currently not possible to explicitly signal RFC 3389 in H.323,
at the last SG16 meeting in Paris it was agreed
( to add
a generic capability specifically for RFC 3389
( However, IMO,
this is unfortunate because it is unnecessary. The way I've seen CN used is
that the transmitter includes CN packets (with static payload type of 13)
and assumes that the receiver will process them if it supports RFC 3389 and
ignore them otherwise. To wit, RTP (RFC 3550, which obsoletes RFC 1889): "A
receiver MUST ignore packets with payload types that it does not
understand." Admittedly, though, this presents problems for less robust
(non-compliant) receivers that ignore payload type.


-----Original Message-----
From: Lyons, Terry [mailto:TLyons at SONUSNET.COM]
Sent: Friday, October 31, 2003 10:16 AM
To: itu-sg16 at
Subject: SIP beats H323?

Is there a standard way in H323 to signal the capability to accept
the comfort noise payload (Appendix II/G.711) with G.711 or G.726?

Appendix VIII of H.245 lists no relevant generic capability.
RFC 3389 only explains how CN is to be signaled with SIP.

- tlyons at +1 732 625-3003 x212

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