draft-allen-sipping-poc-p-answer-state-header

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draft-allen-sipping-poc-p-answer-state-header

• Andrew Allen Research In Motion
• aallen_at_rim.com
• Tom Hallin Motorola
• Jan Holm Ericsson

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P-Answer-State draft overview

• The draft is split out from draft-allen-sipping-po
  c-pheaders-01, renamed and reset to -00 version
• Allows a PTT Server to indicate in a response
  whether the session is established end-to-end or
  only as far as an intermediate node (PTT Server)
• Needed to enable media buffering prior to called
  party answer (early right to speak indication)
• Needed to provide and indication to the caller
  that early right to speak buffering is taking
  place

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P-Answer-State Header

• Values
• Confirmed
• Unconfirmed
• May be included in Responses
• 1xx (typical 183 Session Progress)
• 200 OK
• May be included in a sipfrag or included directly
  in a NOTIFY
• NOTIFY sent as a result of the subscription
  established by REFER
• Security Assumptions
• Trusted PTT Server exists that has knowledge of
  currently selected Answer Mode of the terminating
  UA (PTT Client)
• Trusted PTT Server that originating UA (PTT
  Client) trusts to accept and buffer media

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Changes(from draft-allen-sipping-poc-pheaders-01)

• P-Alerting-Mode header definition has been
  removed
• This extension is progressed separately as
  standards track (draft-willis-sip-answeralert)
• Security considerations improved.
• PUBLISH method has been added to usage table.
• The procedures at the UA text has been split into
  UA-terminal and UA- intermediate-node for better
  clarity.
• A session flow example section added.
• Various nits and editorial corrections.

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Distributed Scenario (PES)
Refer
200 OK
INVITE
INVITE
Answer mode Authorization
INVITE
183 Session Progress (P-Answer-State Unconfirmed)
NOTIFY (SIPFRAG 200 OK P-Answer-State
Unconfirmed)
200 OK (P-Answer-State Unconfirmed)
UA Auto Answers
200 OK
Media
Media Buffering
200 OK
200 OK (P-Answer-State Confirmed)
Media
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Consolidated Scenario (PES)
Refer
200 OK
Answer mode Authorization
INVITE
NOTIFY (P-Answer-State Unconfirmed)
UA Auto Answers
200 OK
Media
Media Buffering
200 OK
Media
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Open Issues

• Generalize to contains an answer instead of
  contains a SDP answer
• Accepted
• Delivering P-Answer-State header to originating
  UA in Consolidated Pre-established Session (PES)
  scenario
• Problem when there is no response containing
  P-Answer-State header to include in the sipfrag
• Include as a header of the initial NOTIFY?
• Include as a header in a dummy 100 TRYING
  sipfrag in the initial NOTIFY?
• Include in the 2xx response to the REFER?
• Something else?
• What to call the Intermediate Node (B2BUA or
  Proxy)
• PTT Server?
• PoC-Intermediate?
• How much to say or define about the general
  Intermediate Node behavior in the draft

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Questions
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Backup Slides
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PoC Session Concepts

• On-Demand Session
• Conventional end-to-end INVITE initiated PoC
  session establishment at Push-to-Talk time
• Pre-established Session
• Pre-established codec negotiation between PoC
  Client and Participating PoC Function using
  INVITE prior to Push-to-Talk time
• Semi-permanent Pre-established INVITE dialogue
  with Participating PoC Function maintained
• Refer within the INVITE dialogue used to initiate
  POC session establishment at Push-to-Talk time

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PoC Concepts and Challenges

• PoC (Push to Talk over Cellular) Concepts
• Sessions established using Push To Talk button
• Right to Speak Indication (e.g Audible tone)
• Half Duplex media
• Talk Burst Control
• 1-1 and Group Calls
• Manual and Auto-Answering terminal
• Manual Answer Override (MAO) for dispatch
• PoC Session establishment latency challenge
• Highly bandwidth constrained cellular networks
• Push-to-talk to Right-to-speak indication latency
  requirement in order of a second

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OMA PoC Architecture
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PoC Server Functions

• Participating PoC Function
• Provides policy enforcement for incoming PoC
  Session (e.g. Access Control, Incoming PoC
  Session Barring, availability status, etc)
• Stores the current Answer Mode, Incoming PoC
  Session Barring and Incoming Instant Personal
  Barring preferences of the PoC Client.
• Controlling PoC Function
• Acts as the Focus for the PoC Session
• May act as an exploder
• Provides the centralized media distribution
• Provides the centralized Talk Burst Control
  functionality

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On-Demand Scenario
INVITE
INVITE
INVITE
Answer mode Authorization
183 Session Progress (P-Answer-State Unconfirmed)
INVITE
200 OK (P-Answer-State Unconfirmed)
200 OK (P-Answer-State Unconfirmed)
PoC Client Auto Answers
Media
Media Buffering
200 OK
200 OK (P-Answer-State Confirmed)
Media