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User to User Key Signaling Protocols. Ellis K Cave Sr. Principal Engineer InterVoice-Brite. DTMF - is it Signaling or Media?. DTMF was designed to provide address signaling at start of call network address signaling DTMF originally turned off during conversation part of call

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user to user key signaling protocols

User to User Key Signaling Protocols

Ellis K Cave

Sr. Principal Engineer

InterVoice-Brite

dtmf is it signaling or media
DTMF - is it Signaling or Media?
  • DTMF was designed to provide address signaling at start of call
    • network address signaling
    • DTMF originally turned off during conversation part of call
    • Left on during call because of tip-ring polarity administration issues

SIP WG

dtmf is it signaling or media1
DTMF - is it Signaling or Media?
  • PSTN service and application vendors discovered DTMF control in late 70s
  • Vendors standardized on the use DTMF for application control during call
    • simple user input mechanism
    • standard across all PSTN terminal device
  • Accidental provision of a standard user input model by the Telco made possible most of today’s complex telephony applications

SIP WG

the infamous octothorpe pound sign
The Infamous Octothorpe (pound sign)
  • Illustrates the confusion between network signaling and user signaling
  • VRU vendors use pound ‘#’ for application control
    • Input field termination
    • “Press pound when you complete your entry”
  • Network vendors use pound ‘#’ as call re-originate
    • “Press pound to disconnect the current LD call, and place another”

SIP WG

network vs user signaling confusion
Network vs User Signaling Confusion
  • To differentiate between network and application functions, network providers had to require that the pound be held for over 2 seconds for network alerts
  • VRU vendors may still interpret a 2-second pound as an application function

SIP WG

address signaling in a packet network
Address Signaling in a Packet Network
  • Current packet session protocols thoroughly deal with address signaling
    • DTMF is not required for address signaling on packet terminals
  • Packet network address signaling standards
    • H.323 - Q.931, H225
    • SIP Invite
  • Smart terminal aggregates address data input from caller
    • Terminal transmits aggregated address data in the call setup signaling message when user presses terminate (OK) key.

SIP WG

dtmf replacement in a packet network
DTMF replacement in a packet network
  • DTMF-type address signaling is not required in a packet network
  • However, some type of user input keystroke signaling IS a requirement in a packet network for interactions with applications and other users
  • What will replace DTMF as application control in a packet network?

SIP WG

most services in the packet network will require standardized user input
Most services in the packet network will require standardized user input.
  • Examples
    • voicemail
    • meet-me conferencing
    • recording/logging services
    • language translation services
    • hearing impaired service
  • To keep these applications simple, user input should be standardized across all terminal types

SIP WG

questions
Questions
  • 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?

Answer

  • The same thing that happens when you press a key on the keyboard of a computer during a SIP call.

SIP WG

user signaling in a packet network
User 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 doesn’t address user input issue
  • Schulzrinne made H.323 to SIP proposal
    • Left out user input indication translation

SIP WG

current proposals for sip dtmf
Current Proposals for SIP DTMF
  • http://www.ietf.org/rfc/rfc2833.txt.
  • http://www.ietf.org/internet-drafts/draft-ietf-sip-info-method-05.txt.
  • draft-kuthan-sip-infopayload-00.txt (expired).
  • 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.
  • http://www.ietf.org/internet-drafts/draft-agrawal-sip-h323-interworking-reqs

SIP WG

where should you put user input
Where should you put User Input?
  • Should it go in the signaling protocol (SIP)?
    • The current Info Method proposals propose this approach
    • Does an application protocol belong in the session set-up/teardown signaling?
    • SIP Info Method has the right transport characteristics
      • guaranteed delivery
      • single packet
  • Should it go in the session description protocol (SDP)?
    • SDP currently only sets up media sessions

SIP WG

where should you put user input1
Where should you put User Input?
  • Perhaps User Input needs its own session specifically for user signaling.
  • If an application using SIP expects to need user input (and most will), the user agent should use SDP to set up a user input session
  • User input sessions will be as common as streaming media sessions

SIP WG

user key input transport protocol requirements
User Key Input Transport Protocol Requirements
  • Keystroke-based
  • Requires guaranteed delivery
    • no dropped packets
  • Requires guaranteed sequencing
    • receiver should be able to get transmitted input events in transmit order
  • Duration information should be an option
  • User input signaling protocol should be the same whether it is a SIP phone, a PC, or a cell phone!

SIP WG

what are the choices
What are the Choices?
  • RTP stream
  • Info Method
  • New SDP session protocol

SIP WG

rtp streaming for user key input
RTP streaming for User Key Input
  • Pros
    • Existing protocol
    • Guaranteed Sequencing
  • Cons
    • User Input is not a streaming function
      • single keystroke events
    • RTP is not guaranteed delivery
    • Overly complex protocol for simple keystrokes
      • RTSP, stats, jitter buffers, etc
      • Simple text chat apps would require RTP stack
    • User Input needs to be a separate session from audio stream

SIP WG

sip info method for user key input
SIP Info Method for User Key Input
  • Pros
    • Existing protocol
    • Guaranteed delivery
    • Simple mechanism (part of SIP)
  • Cons
    • Architecturally, application and user data should NOT be in the signaling channel
    • Future 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?

SIP WG

new sdp session for user key input
New SDP Session for User Key Input
  • Pros
    • Allows selection of appropriate transport protocol for reliable keystroke delivery
    • Separate session for User Key Input
    • Allows redirect & multi-unicast, etc.
  • Cons
    • Need to define new SDP protocol for User Key Input
    • Must use SDP to set up User Key Input session

SIP WG

sdp supports
SDP supports
  • Video
  • Audio
  • Application
  • Data
  • Control
  • Which type of session is most appropriate?

SIP WG

gateway requirements
Gateway Requirements
  • Gateway is the intelligent proxy for the dumb black phone in a SIP call.
  • Gateway never sees PSTN address signaling from terminal, only user key input
  • Job of the gateway is to convert DTMF to the new SIP User Key Input protocol
  • Gateway sets up User Key Input SDP session

SIP WG

avoid the wap wml hdml webclip debacle
Avoid the WAP/WML/HDML/WebClip Debacle
  • Different protocol for each type of device
  • To avoid chaos, the User Key Input protocol should be standardized for all packet terminal devices.
  • The “one” numeric key should produce the same message in the User Key Input session on all devices.

SIP WG

conclusions
Conclusions
  • SIP architecture needs a User Key Input mechanism
  • Best choice is a separate SDP session
  • Could be “application’ or “control” session type
  • User Input should be standardized across all terminal devices
  • Keystroke/event message map defined in standard across all terminal device types

SIP WG

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