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Re: [MMUSIC] Transport of "Flash-hook"

Martin Taylor <Martin.Taylor@metaswitch.com> Fri, 10 June 2016 08:49 UTC

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From: Martin Taylor <Martin.Taylor@metaswitch.com>
To: Brian Rosen <br@brianrosen.net>, "mmusic@ietf.org" <mmusic@ietf.org>
Thread-Topic: [MMUSIC] Transport of "Flash-hook"
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Date: Fri, 10 Jun 2016 08:49:02 +0000
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Subject: Re: [MMUSIC] Transport of "Flash-hook"
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Signalling of flash-hook is an important aspect of PSTN Emulation with IMS.  There are a bunch of mid-call services that must be supported for POTS such as call transfer and three-way calling which rely on being able to signal flash-hook.

In my experience, most PSTN Emulation implementations use SIP INFO requests to signal flash-hook.  To my knowledge, this has never been standardized but there have been I-Ds on the topic, e.g. draft-hwang-sipping-infomidcall-00 and draft-kaplan-sip-info-use-cases-01.

Many analog telephone adapters support the SIP INFO method of signalling flash-hook.

Martin

-----Original Message-----
From: mmusic [mailto:mmusic-bounces@ietf.org] On Behalf Of Brian Rosen
Sent: 02 June 2016 20:02
To: mmusic@ietf.org
Subject: [MMUSIC] Transport of "Flash-hook"

Back in RFC2833, the DTMF tones section, code 16 was defined for “Flash”, the signal caused by a momentary depression of the hook-switch in a POTS phone.  When 2833 was obsoleted by 4733, flash was dropped, although the code 16 was reserved.

We have a use case in NENA (9-1-1 emergency stuff) where existing systems use flash interspersed wth tones in signaling dialing events which are not interpreted by the UA that receives them, but are instead transported to a device that creates appropriate SIP signaling for the dialing events initiated.  We have no other way to transport flash to interwork with our newer SIP based emergency calling systems.

I’m prepared to write a draft that restores code 16 for flash, as it was in 2833, but wanted to hear any objections to doing that.

Brian
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