DTMF & Universal User Key Input Skip Cave InterVoice-Brite Inc.
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Transcript of DTMF & Universal User Key Input Skip Cave InterVoice-Brite Inc.
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DTMF &Universal User Key Input
Skip Cave
InterVoice-Brite Inc.
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48th IETF SIP WG 2
DTMF Origins - The Fortuitous Mistake
• DTMF was designed to provide address signaling to CO in PSTN at start of call– Speed user address input (rotary dial was slow)
– DTMF originally turned off during conversation part of call
– Left on during call because of tip-ring polarity administration issues
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48th IETF SIP WG 3
DTMF Origins - The Fortuitous Mistake
• Created simple, universal user input mechanism for all devices on the PSTN network – end-to-end signaling
– standard across all PSTN terminal devices
• PSTN service and application vendors discovered DTMF availability during call in late 70s & began using DTMF for application control
• Accidental provisioning of an end-to-end standard for user input by the Telco made possible most of today’s automated telephony applications & services
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48th IETF SIP WG 4
DTMF Usage Today
• Virtually all PSTN terminals today have a standard 12-key keypad as a minimum
• DTMF for Address signaling is ubiquitous• Universal User Input mechanism - DTMF has
become the standard user input mechanism for all types of PSTN voice terminals to interact with services and applications
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48th IETF SIP WG 5
DTMF - Is it Network or Application Signaling?
• DTMF address signaling is always terminated in the local CO
• All DTMF after call setup is application signaling• Edge applications
– IVR
– Voicemail
• Network applications– Calling Card
– Universal Messaging
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48th IETF SIP WG 6
Address Signaling in a Packet Network
• Current packet session protocols thoroughly deal with address signaling
• Packet network address signaling standards– H.323 - Q.931, H225
– SIP Invite
• The original function of DTMF (address signaling) is not needed in packet network
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48th IETF SIP WG 7
The Universal User Input Problem
• Most (if not all) packet terminal devices do NOT use DTMF for user input signaling
• Some method for user input keystroke signaling IS a requirement in a packet network for interactions with applications and other users
• Application providers in the packet network need a standardized way to deal with key input from all types of terminal devices that reside both in the PSTN AND in the packet network.
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48th IETF SIP WG 8
Questions
• From the perspective of an application provider in the packet network - What do you want to have happen when a user presses a button on the keypad of a SIP desk phone during a SIP call ?
• A cell phone in the PSTN?
Answer• The same thing that happens when you press a key
on the keyboard of a computer during a SIP call.
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48th IETF SIP WG 9
Current DTMF/SIP Transport Proposals
• Originally focused on carrying DTMF across packet network to be reconstructed for PSTN
• Started discussing delivery of DTMF to application platforms in the packet network
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48th IETF SIP WG 10
User Input Signaling in a Packet Network
• H.323 defines user input indication - H.245– Intended specifically for DTMF
– Assumes 16-key device 0-9, *, #, and A-D
• SIP User Input under discussion• Schulzrinne made H.323 to SIP proposal
– Left out user input indication translation
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48th IETF SIP WG 11
Requirements for User Key Input Mechanism
• End-to-end event delivery• Single-event transmission protocol
– perhaps like mid-call triggers for applications
– Keystroke-based
• Guaranteed delivery– no dropped key events
• Guaranteed sequencing– receiver should be able to determine order of transmitted
input events
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48th IETF SIP WG 12
Requirements for User Key Input Mechanism
• Should DTMF Duration, Time-Stamp & Level information be an option?– Primarily required for DTMF reconstruction
– Packet terminal devices will probably not be capable of providing keystroke duration, time-stamp & level information (PC)
– Applications that must use both PSTN & Packet terminals should not rely on duration, exact event times, or levels, so these should not be in Universal Key Input protocol (RFC 2833 sec. 3.1)
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48th IETF SIP WG 13
Requirements for User Key Input Mechanism
• Media/Keystroke Separation– Keystroke events should be in isolated session
– NOT combined with audio streaming
• Many applications will not require media streams, only keystroke events
• Some applications will send media streams to one endpoint, and keystroke events to another endpoint– Should be able to re-invite keystroke streams to other
endpoints
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48th IETF SIP WG 14
What are the Choices for User Input?
• Info Method• RTP stream• Other SDP session protocol
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48th IETF SIP WG 15
SIP Info Method
• The current Info Method proposals– http://www.ietf.org/internet-drafts/draft-ietf-
sip-info-method-05.txt.– http://www.ietf.org/internet-drafts/draft-
choudhuri-sip-info-digit-00.txt.– http://www.ietf.org/internet-drafts/draft-
culpepper-sip-info-event-00.txt.– draft-kuthan-sip-infopayload-00.txt (expired)
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48th IETF SIP WG 16
SIP Info Method for User Key Input
• Pros– Existing, efficient protocol– Guaranteed delivery of Single Events– Simple mechanism (part of SIP)
• Cons– Architecturally, application and user data should NOT be in the
signaling channel• This point is probably moot for PSTN-PSTN transport, but it is
significant for UUKI
– Applications using redirection and replication of user input for multi-party conferencing would be prevented
• How do you redirect or multicast the SIP session Info Messages?
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48th IETF SIP WG 17
RTP “Telephone Event” Payload
• The current RTP Stream Proposal for DTMF– http://www.ietf.org/rfc/rfc2833.txt– RFC 2833 defines a method to transport PSTN
audio and in-band signaling tones across a packet network - primarily for re-insertion into the PSTN
– Solves problem of tone-distorting compression protocols
– Solves problem of reconstruction of waveforms with correct timing relationships
– Henning has done an elegant job of solving the PSTN to Packet to PSTN transport problem
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48th IETF SIP WG 18
RTP “Telephone Event” Payload for User Key Input
• Pros– Uses Existing protocol
– Guaranteed Sequencing
– Focused on PSTN to Packet to PSTN - DTMF transport
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48th IETF SIP WG 19
RTP “Telephone Event” Payload • Cons
– User Input is not necessarily a streaming function• single keystroke events
– RTP is not guaranteed delivery in basic form (can drop keystroke events)
• RFC 2198 provides a potential redundancy method for improving relibility
– Overly complex protocol for simple keystrokes• RTSP, statistics, jitter buffers, redundancy, etc
• Simple text chat apps would require RTP stack
• http://www.ietf.org/rfc/rfc2833.txt Sec 3.1
– User Input needs to be a separate session from audio stream– Should all terminal types be required to provides keystrokes
using 2833?
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48th IETF SIP WG 20
RTP “Telephone Event” Payload
• RFC 2833 Does not address (at least not explicitly) the Universal User Input problem
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48th IETF SIP WG 21
The Problem
• RFC 2833 is certainly a good way to send DTMF across a packet network for reconstruction in the PSTN. Not so good for simple user key input
• All of the Info Method proposals are reasonable ways to transport user input to a packet terminal, but they use SIP Info Message session signaling - not appropriate for application usage.
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48th IETF SIP WG 22
The Problem
• These proposals aren’t appropriate for providing a universal user input mechanism across both PSTN and Packet terminal devices
• Application providers in the packet world want the same universal input model that the PSTN has
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48th IETF SIP WG 23
The Solution
• Define SDP Session Specifically for User Key Input• Pros
– Provides separate session for User Key Input– Allows selection of appropriate transport protocol for reliable
keystroke delivery– Allows redirect & multi-unicast, etc. of keystroke events– Could allow optional timestamp & duration information for
reconstruction of DTMF
• Cons– Need to select/define new SDP protocol for User Key Input– Must set up specific session for User Key Input
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48th IETF SIP WG 24
Issues
• Application providers need an end-to-end Universal Key Input model for terminal devices in SIP network just like in PSTN
• If an application using SIP needs user input (and most will), the user agent should use SDP to set up a user input session
• User input sessions will be more common than streaming media sessions in the packet network
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48th IETF SIP WG 25
Issues
• Gateway may have to sent two different representations of user input - one in RFC 2833 or Info Method form (whichever is used for DTMF transport) AND a User Key Input session
• May want to consider an event aggregation mechanism in future work
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48th IETF SIP WG 26
Conclusions
• There are TWO problems– DTMF transport across a packet network– Universal User Key Input mechanism
• The requirements for the solution to these two problems differ
• RFC 2833 or Info Method will work for the specific problem of PSTN-Packet-PSTN Audio & In-band signaling transport
• Neither RFC 2833 or the various Info Methods proposals are appropriate for a universal terminal key input mechanism like that available in the PSTN
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48th IETF SIP WG 27
Conclusions
• Packet SIP architecture needs a Universal User Key Input mechanism
• Best choice is a to define a new SDP session specifically for User Key Input
• Need to select most appropriate protocol for User Input SDP session
• User Input should be standardized across all terminal devices– numeric “One” key produces same result for all devices