[SIPForum-discussion] What is the function of telephone-event?

Tue Mar 18 02:50:57 UTC 2008

HI Andrea, 

The following extracted is from RFC2833. Hope it helps to answer your question,

RTP packets using the payload format defined in this specification

   are subject to the security considerations discussed in the RTP

   specification (RFC 1889 [1]), and any appropriate RTP profile (for

   example RFC 1890 [19]).This implies that confidentiality of the media

   streams is achieved by encryption. Because the data compression used

   with this payload format is applied end-to-end, encryption may be

   performed after compression so there is no conflict between the two

   operations.

   This payload type does not exhibit any significant non-uniformity in

   the receiver side computational complexity for packet processing to

   cause a potential denial-of-service threat.

   In older networks employing in-band signaling and lacking appropriate

   tone filters, the tones in Section 3.14 may be used to commit toll

   fraud.

Best Regards,

Eugene

________________________________

From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Andrea Puddu
Sent: Monday, March 17, 2008 05:59 PM
To: Mark Holloway; 'Steve Langstaff'; discussion at sipforum.org
Subject: Re: [SIPForum-discussion] What is the function of telephone-event?

Hi all,

we have to perform some tests to verify the impact of using DTMF in-band with g729.
Do you know which network performance parameters could affect the functioning of DTMF in-band with g729?
For example ... jittering?delay?packet loss?what else?

I am asking because it's not totally clear to me why DTMF in-band could not work together with g729.

Thanks,

Andrea

________________________________

From: mh at markholloway.com
To: androjoker at hotmail.com; steve.langstaff at citel.com; discussion at sipforum.org
Subject: RE: [SIPForum-discussion] What is the function of telephone-event?
Date: Thu, 6 Mar 2008 08:08:07 -0700

G729 does not support inband DTMF because the codec compresses the audio.  You must use out of band.  Therefore, telephone-event is used to tell the other endpoint how it should receive DTMF tones.  If you are using G711 you should be able to support inband.  If you are using a compressed codec you should consider using out of band.  This can be RFC 2833 or SIP Info Method.  Regardless, not supporting telephone-event reflects a poor SIP implementation in my opinion. 

From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Andrea Puddu
Sent: Thursday, March 06, 2008 7:09 AM
To: Steve Langstaff; discussion at sipforum.org
Subject: Re: [SIPForum-discussion] What is the function of telephone-event?

Thanks Steve.

Why did you talk about low bit-rate codec? I understood the matter about dtfm out of band, but it is not clear to me why it should impact low bit rate codec (e.g. g729).

Thanks,

Andrea

________________________________

Subject: RE: [SIPForum-discussion] What is the function of telephone-event?
Date: Thu, 6 Mar 2008 05:01:34 -0800
From: steve.langstaff at citel.com
To: androjoker at hotmail.com; discussion at sipforum.org

"telephone-event" is a method for passing e.g. DTMF signalling in an RTP stream.

The "101" (or any payload type in the range 96-127) refers to a dynamic payload type.

So a stream that negotiates to use "101 telephone-event" may e.g. pass keypresses

using RTP payload type 101 rather than "in-band".

The risks you face in removing telephone event support are that if you are using a

low bitrate codec such as G.729, or you are using equipment that does not expect

to see DTMF "in-band" then users may lose the ability to control e.g. IVR equipment.

________________________________

	From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Andrea Puddu
	Sent: 06 March 2008 12:15
	To: discussion at sipforum.org
	Subject: [SIPForum-discussion] What is the function of telephone-event?

	Hello guys,

	as the network here does not completely support "telephone event" in SDP they asked me to set up phones to not include "telephone event".
	I have looked at some RFCs .... but I couldn't understand what the telephone events are useful to.

	Do you see any risk to remove the telephone event, in particular the 101 telephone event?

	thanks 1000.

	Andrea

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