OMA PoC Release

As the cellular networks evolve, they will be able to provide other more advanced IP-based real-time services than the plain voice services offered in the OMA PoC Release 1 specifications. Advanced services should, in this context, be seen as services that are more demanding in terms of bit rate and delay, and that offer improved possibilities of person-to-person communication and thus increase perceived user value compared to a plain voice call. OMA is trying to make use of the new opportunities promised by the evolved cellular networks by continuing the development of the PoC communication service and for instance introducing multimedia capabilities in the PoC service offering. One example of a more advanced communication method included in the OMA PoC Release 2 specifications that promises to increase the perceived user value is PoC video sharing. PoC video sharing is here used to exemplify the evolution of OMA PoC.

The term PoC video sharing refers to sending and receiving of multimedia talk bursts containing video and voice to other PoC video sharing enabled mobile terminals in a PoC session. The PoC video sharing communication method can therefore be seen as a real-time person-to-person video messaging service. PoC video sharing enriches the voice communication by adding the ability to send video streams of either something you are talking about or the talker's face that enables other users to see and interpret the facial expression of the talking user.

PoC video sharing is based on the plain OMA PoC voice service. This means that the video stream of the PoC video sharing session is:

• sent using an IETF standardized protocol suite (RTP/UDP/IP);

• controlled by a media burst control mechanism (i.e. a multimedia version of the talk burst control mechanism in OMA PoC Release 1).

The right to transmit video to all PoC users in a PoC video sharing session can be requested by any of the PoC users in the PoC video sharing session, at any given time, given that no other user is currently transmitting video. Hence, concurrent bidirectional video streams are not supported in PoC video sharing; instead the video stream is always half-duplex as the voice stream in PoC. Two modes of operation are supported. The first method

Figure 8.11: PoC video sharing. (a) Synchronous mode of operation. (b) Asynchronous mode of operation.

could be called synchronous mode of operation. In this mode of operation the voice and the video streams are coming from one source. During transmission of synchronized voice and video no other participant in the PoC video sharing session can be granted the right to transmit video or voice. The voice and video can be made lip-synchronized. The second method could be called asynchronous mode of operation. In this mode of operation only video is streamed from one PoC video sharing enabled client, while the other PoC clients in the PoC video sharing session can request and be granted the right to speak. Figure 8.11 describes the two different modes of operation.

The OMA PoC Release 2 specifications also support PoC communication methods that enable the exchange of other non-real-time media types like images, text and files such as prerecorded video clips. Non-real-time media types are best transported using TCP/IP. Hence, the main difference compared to the PoC video sharing method is the use of TCP/IP for media transfer rather than the RTP/UDP/IP protocol suite. The application layer protocol proposed to be used for the image, text and file transfer is MSRP that also is used in Multimedia Telephony, 3GPP CSICS (see Section 8.1) and OMA Instant Messaging (see Section 8.3). It should also be noted that the OMA PoC Release 2 specifications extend the OMA PoC communication service with a large number of other enhancements beside the multimedia capabilities. The list below presents a few of the proposed enhancements.

• A 'PoC media box', which is a PoC functionality to store media burst and related information (e.g. date and time, sender identity) on behalf of a PoC user.

• Interworking functionality allowing other non-OMA push-to-talk networks to inter-work with the OMA PoC service infrastructure.

• Enhanced PoC session handling including the possibility of moderator controlled PoC sessions to enable systems with a fleet dispatcher that is in control.

• Enhanced PoC group handling, for example creation of PoC group sessions, that includes multiple PoC groups and creation of PoC group sessions based on dynamic data such as presence state of the individual PoC users.

• Quality of experience and crisis handling which calls for quality of service management and priority framework that allows the PoC service infrastructure to differentiate the end-user experience provided to individual PoC users on a subscription base and type of session request.

• Full-duplex call follow-on procedure that allows a half-duplex PoC session to be changed into a full-duplex Multimedia Telephony session or a CS call.

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