Paul,

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@sonusnet.com +1 732 625-3003 x212

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

Terry,

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 (http://avguest@ftp3.itu.int/av-arch/avc-site/0309_Par/AVD-2410.zip) to add a generic capability specifically for RFC 3389 (http://ftp3.itu.int/av-arch/avc-site/0309_Par/AVD-2366.zip). 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.

Paul

-----Original Message----- From: Lyons, Terry [mailto:TLyons@SONUSNET.COM] Sent: Friday, October 31, 2003 10:16 AM To: itu-sg16@external.cisco.com 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@sonusnet.com +1 732 625-3003 x212