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OMA PoC Overview and draft-allen-sipping-poc-p-headers

Explore the latest OMA PoC specs focusing on Push-to-Talk sessions, architecture, and latency challenges in SIP-based networks. Learn about PoC servers, floor control, answering modes, and more.

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OMA PoC Overview and draft-allen-sipping-poc-p-headers

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  1. OMA PoC Overview anddraft-allen-sipping-poc-p-headers Andrew Allen: Research In Motion Tom Hiller: Lucent Technologies

  2. Latest Public OMA PoC Specs • http://member.openmobilealliance.org/ftp/Public_documents/POC/Permanent_documents/OMA-AD-PoC-V1_0-20050308-D.zip • http://member.openmobilealliance.org/ftp/Public_documents/POC/Permanent_documents/OMA-TS-PoC_ControlPlane-V1_0-20050308-D.zip • http://member.openmobilealliance.org/ftp/Public_documents/POC/Permanent_documents/OMA-TS-PoC_UserPlane-V1_0_16-20050308-D.zip

  3. PoC Concepts • PoC (Push to Talk over Cellular) Concepts • Supports “PoC Sessions” featuring half duplex media from one participant to other participants. PoCv1 focuses on audio. • Uses SIP signaling, and has numerous references to 3GPP/2 IMS/MMD, but in no way precludes non IMS/MMD based SIP networks. Also, OMA is access network agnostic. • Can set up a PoC session to one user, a URI list of users, or a (flat) pre-arranged group of users • Floor Control arbitrates one speaker with the right to speak; an indication (e.g., audible tone) indicates when to speak • Manual and Auto-Answering modes supported • Manual Answer Override (MAO) supported, e.g., for emergency dispatch purposes • Confirmed and an unconfirmed indication to speak

  4. OMA PoC Architecture

  5. PoC Server Functions • Participating PoC Function (“PF”) • SIP application residing in the home network of the user • 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. • Can arbitrate the active PoC sessions for simultaneous PoC sessions • Controlling PoC Function (“CF”) • A SIP application that can invite requested users or determine the participants of a group • Acts as the Focus for the PoC Session • Provides a centralized media distribution • Provides a centralized floor control functionality • May buffer some talk bursts

  6. “On Demand” Call Model • On-Demand Session • Conventional end-to-end INVITE initiated PoC session establishment time • An INVITE is an implicit floor request at establishment and a 200 “OK” response can carry an SDP based floor grant indication.

  7. “Pre-established Session” • Pre-established Session • Uses a long held SIP session (setup with an INVITE) between the PoC Client and its Participating PoC Function prior to Push-to-Talk time; negotiates codecs, floor control protocol, etc. • Call establishment request is an in-dialog REFER request to add users to the pre-established session. • REFER is an implicit floor request • Makes significant use of an OMA specified floor control (and if desired SIP notifications) to convey session establishment and the PoC Session URI • Fewer bytes than an INVITE and possibly no SIP at the mobile terminating side at PoC session setup

  8. Latency Challenge • Dormant activation and limited over-the-air connection bandwidth offer challenges to PoC • PoC indication to speak latency requirement is typically to be under two seconds for the unconfirmed indication in auto answer mode • Unconfirmed floor control indication permits the originating user to speak before a terminating user responds to SIP signaling; CF PoC server buffers

  9. PoC Server X PoC Server B PoC Client B PoC Server A PoC Client A Example Scenario INVITE (P-Alerting-Mode: MAO) MAO Authorization INVITE (P-Alerting-Mode: MAO) INVITE (P-Alerting-Mode: MAO) Answer mode Authorization 183 Session Progress (P-Answer-State: Unconfirmed) INVITE (P-Alerting-Mode: MAO) 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

  10. draft-allen-sipping-poc-p-headers • P-Alerting-Mode • Allows an originating PoC Client or PoC Server to request a particular answering mode (i.e., Manual, Auto, MAO). • P-Answer-State • Allows a PoC Server to indicate in a response whether the session is established end-to-end or only as far as an intermediate node. In PoC this is the terminating PoC PF 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

  11. P-Alerting-Mode • Values • Manual • Auto • MAO • Methods • INVITE • REFER • Security Assumptions • Authorization Mechanisms for requested mode • Integrity Security between PoC Server and PoC Client if PoC Server performs the Authorization

  12. P-Answer-State • Values • Confirmed • Unconfirmed • May be included in Responses • 1XX (typical 183 Session Progress) • 200 OK • Responses may or may not contain SDP • May be included in a SIP Frag • NOTIFY sent as a result of subscription established by REFER • Security Assumptions • Trusted PoC Server has knowledge of currently selected Answer Mode of the terminating PoC Client • Originating PoC Client relies on a PoC Server to buffer media

  13. Thank you Questions?

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