OMA PoC Overview and draft-allen-sipping-poc-p-headers Andrew Allen: Research In Motion Tom Hiller: Lucent Technologies

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

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

OMA PoC Architecture

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

“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.

“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

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

Example Scenario MAO Authorization Answer mode Authorization PoC Server A PoC Server X PoC Server B PoC Client B PoC Client A 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

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

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

P-Answer-State Values May be included in Responses 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

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