Hi,
I see your point.
But if this is right, then why does H323 protocol support silence suppression and echo
cancellation parameters?
On the other hand, in case of fax fallback to G711 coder (if T38 is not supported), there is a
need to specify to remote device that "echo cancelation is ON, and silence suppression is OFF".
AFAIK fax will not be properly passed if silence suppression is not turned off.
And this, I beleive, is the reason why draft-ietf-sipping-realtimefax-00.txt makes use of
"ecan" and "silenceSupp" SDP attributes.
Also there is a following sentence in H323-SIP interworking draft :
"A fmtp SDP attribute for silence suppression SHOULD be defined if
silence suppression is on."
Is it not valid any more?
Best regards,
Alex Agranov
> -----Original Message-----
> From: David R. Oran [mailto:oran@cisco.com]
> Sent: Tuesday, February 04, 2003 5:53 PM
> To: Alex Agranov; 'sip@ietf.org'
> Subject: Re: [Sip] Silence Suppression in SDP for VoIP
>
>
> There are no such parameters in SDP nor SIP because both of these are
> algorithm options for one end of a media stream. The source
> of the stream
> does these by itself and therefore they have no end-to-end
> significance. As
> a consequence there is no need for the receiver to know
> anything about Vad
> or ecan parameters of the transmitter, or vice versa.
>
> The reason these exist in MGCP and Megaco is because those are device
> control protocols intended for comand and control of an endpoint, as
> opposed to peer signaling protocols like SIP.
>
> --On Tuesday, February 04, 2003 12:24 PM +0200 Alex Agranov
> <sagranov@COMGATES.co.il> wrote:
>
> >
> > Hi,
> >
> > I tried to ask this question in sip-implementors maillist but nobody
> > could answer it there...
> >
> > What is the proper way to indicate Silence Suppression and Echo
> > Cancelation coder parameters in SDP? In MGCP these parameters are
> > passed in LCO element, but for SIP Offer/Answer model these
> parameters
> > should be passed in SDP. Right?
> >
> > There is RFC3108 that defines "ecan" and "silenceSupp"
> attributes, but it
> > applies to VoATM. Is it applicable to VoIP too?
> >
> > Some late drafts, e.g.
> draft-ietf-sipping-realtimefax-00.txt, seem to
> > assume RFC3108 attributes are valid for VoIP. Is this correct?
> >
> > Best regards,
> > Alex Agranov
> > ---
> > Senior Software Engineer
> > COMGATES Ltd.
> > 15 Hagalim Avenue
> > Herzliya, 46725
> > Israel
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>
> ------------------------
> David R. Oran
> Cisco Systems
> 7 Ladyslipper Lane
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> Email: oran@cisco.com
>