User to User Key Signaling Protocols

1
User to User Key Signaling Protocols

• Ellis K Cave
• Sr. Principal Engineer
• InterVoice-Brite

2
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

3
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 todays
  complex telephony applications

4
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

5
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

6
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.

7
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?

8
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

9
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.

10
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 doesnt address user input issue
• Schulzrinne made H.323 to SIP proposal
• Left out user input indication translation

11
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-choudhur
  i-sip-info-digit-00.txt.
• http//www.ietf.org/internet-drafts/draft-culpeppe
  r-sip-info-event-00.txt.
• http//www.ietf.org/internet-drafts/draft-agrawal-
  sip-h323-interworking-reqs

12
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

13
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

14
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!

15
What are the Choices?

• RTP stream
• Info Method
• New SDP session protocol

16
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

17
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?

18
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

19
SDP supports

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

20
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

21
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.

22
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