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

2. Latest Public OMA PoC Specs

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”
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. 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

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 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

12. 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

13. Thank you
Questions?