OMA PoC Release 1 Architecture

Figure 8.6 shows the high-level architecture of an OMA PoC Release 1 compliant system. The system includes a number of nodes and logical functions.

• The CSCF implements the S-CSCF, I-CSCF and P-CSCF functionality that provides SIP signaling, routing and registration.

Charging

Diameter

Lis&ntgroupManagement , XCAP

CAI3G

Charging

Diameter

Lis&ntgroupManagement , XCAP

CAI3G

Diameter

' IMS PTT Application *

Diameter

' IMS PTT Application *

Signaling

Signaling

Media

RTP/RTCP

CD X

03 n CD

Figure 8.6: The logical architecture of OMA PoC Release 1.

• The HSS implements functionality for authentication, location query/updates and subscriber profile storage.

• The charging function post-processes the charging information, for instance delivered by the PoC server. The charging function creates the Call Data Records (CDR) and sends them towards external billing systems.

• The provisioning function is used for the provision of user related information to the PoC client.

• The PoC server (the OMA PoC AS) is a crucial part of the system. It contains two parts, the PoC logic part and the media handling part. The PoC logic part authorizes PoC users to initiate a PoC session through the use of the invited users' PoC service settings, e.g. incoming session barring (similar to the Multimedia Telephony supplementary service communication barring, see Section 4.7.7) and answer mode, as well as authorizing a user to make a group call by providing the media handling part of the group member list. The media handling part multiplies the speaker's bitstream to multiple streams for the receiving PoC users. Another important functionality of the media handling part is that it handles talk burst control, i.e. it secures that only one user speaks at a time.

• The PoC client on the mobile terminal.

• The OMA PoC network uses a group list management functionality to handle the PoC groups. The OMA PoC network may also include the presence enabler. Presence and list management are presented in Section 8.4.

In order to provide the PoC users with the possibility of doing inter-operator PoC calls the PoC server that implements the application level network functionality for the PoC service must be able to perform different roles. The two roles defined are the controlling PoC function

PoC Server A

PoC Server A

Network A
Network B

Figure 8.7: The relationship between PoC server, controlling PoC function, participating PoC functions and the PoC clients in a group session with four PoC clients.

and the participating PoC function. The PoC server can perform one of the two roles or both roles at the same time in a PoC session. The determination of the PoC server role takes place during the PoC session establishment and lasts for the duration of the whole PoC session. Figure 8.7 shows the relationship between the PoC servers, controlling PoC function, participating PoC functions and the PoC clients.

There can be only one controlling PoC function per PoC session and thus only one PoC server performing the controlling PoC function per PoC session since it is the controlling PoC function that is the 'central' intelligence in the PoC network and for instance insures that only one PoC user is talking at a given time. The controlling PoC function has N number of SIP sessions and media and talk burst control communication paths in one PoC session, where N is the number of participants in the PoC session. The controlling PoC function will not have any direct communication to the PoC client for PoC session signaling, but will interact with the PoC client via the participating PoC function for the PoC client.

There will be N participating PoC functions in the PoC session. Hence, every PoC client in the PoC session is connected to a participating PoC function so the physical unit of the PoC server may have to act as the logical unit of the participating PoC function for a multitude of PoC clients during the PoC session. A PoC server performing the participating PoC function always has a direct communication path with a PoC client and a direct communication path with the controlling PoC function (which may be located in the same physical PoC server) for PoC session signaling.

The controlling PoC function will normally route media and talk burst control messages to the PoC client via the participating PoC function for the PoC client. However, local policy in the PoC server performing the participating PoC function may allow the controlling PoC function to have a direct communication path for media and talk burst control signaling to each PoC client.

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