4 Architecture considerations

32.2723GPPCharging managementPush-to-talk over Cellular (PoC) chargingRelease 17Telecommunication managementTS

4.1 High level PoC architecture

Figure 4.1.1 depicts the PoC reference architecture, as described in TR 23.979 [200].

Figure 4.1.1: PoC service elements in the IMS architecture

NOTE: The I-CSCF and HSS are not shown in figure 4.1.1 for the sake of simplicity.

The OMA-AD-POC [203] leverages IMS as the underlying SIP-based IP-core network. The PoC Server implementing the application level network functionality for the PoC service is essentially seen as an Application Server (AS) from the IMS perspective. Consequently, communications between the IMS core and the PoC Server utilize the ISC interface defined in TS 23.228 [201].

The XML Document Management Server (XDMS) is used by the PoC users to manage groups and lists (e.g. contact and access lists) that are needed for the PoC service. In the IMS architecture, the Ut interface provides these functions, hence communications between the XDMS and the UE (PoC Client) utilize the Ut interface. The XDMS is seen as a separate AS that could be also connected to other entities in addition to PoC Server (e.g. to Presence Server).

As described in the following clauses only the PoC Server is relevant for charging.

Editor’s note: The figure may be replaced by an OMA version.

4.1.1 PoC functional entities

In the next two subclauses the PoC functional entities, PoC Client and PoC Server are presented as described in OMA‑AD-POC [203]. Also different roles of the PoC Server that impact the PoC charging architecture are described.

4.1.1.1 PoC Client

The PoC Client resides on the mobile terminal and is used to access PoC service. In figure 4.1.1.2.1, the UE is acting as a PoC Client.

4.1.1.2 PoC Server

The PoC Server implements the application level network functionality for the PoC service.

The PoC Server may perform a controlling PoC function or participating PoC function. The controlling PoC function and participating PoC function are different roles of the PoC Server. The figures in this clause show the flow of signalling traffic and media and media-related signalling traffic between controlling PoC function and participating PoC function in various configurations.
Unless otherwise mentioned, the traffic flows shown in each figure apply to both signalling traffic and media and media-related signalling traffic in that configuration.
Figure 4.1.1.2.1 shows the distribution of the functionality during a 1-1 PoC session in a single network.
A PoC Server may perform both a controlling PoC function and a participating PoC function at the same time.

Figure 4.1.1.2.1: Relationship between controlling PoC function,
participating PoC functions and the PoC Clients for 1-1 PoC session in a single network

The determination of the PoC Server role (controlling PoC function and participating PoC function) takes place during the PoC session set-up and lasts for the duration of the whole PoC session.
In case of 1-1 PoC session and ad-hoc PoC group session the PoC Server of the inviting user shall perform the controlling PoC function. I
n case of the chat PoC group and pre-arranged group session the PoC Server owning/hosting the group identity shall perform the controlling PoC function.

Figure 4.1.1.2.2: Relationship between the controlling PoC function,
participating PoC function and PoC Clients for 1-1 PoC session in a multiple network

In a PoC session there shall be only one PoC Server performing the controlling PoC function.
There can be one or more PoC Servers performing the participating PoC function in the PoC session.
Figure 4.1.1.2.2 shows the distribution of the functionality during a 1-1 PoC session in a multiple network environment.

The PoC Server performing 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 number of participants in the PoC session.
The PoC Server performing the PoC controlling function has no direct communication to the PoC Client for PoC session signalling, but interacts with the PoC Client via the PoC Server performing the participating functioning for the PoC Client.

The PoC Server performing the controlling PoC function normally also routes the media and media-related signalling such as talk burst arbitration to the PoC Client via the PoC Server performing the participating functioning for the PoC Client. However, local policy in the PoC Server performing the participating PoC function may allow the PoC Server performing the controlling PoC function to have a direct communication path for media and media-related signalling to each PoC Client.
Figure 4.1.1.2.3 shows the signalling and media paths in this configuration for a controlling PoC function, participating PoC function and PoC Client served in the same network.

A PoC Server performing the participating PoC function has always a direct communication path with a PoC Client and a direct communication path with the PoC Server performing the controlling PoC function for PoC session signalling.

Figure 4.1.1.2.3: Direct media flow between controlling PoC function and PoC Client

Figure 4.1.1.2.4 depicts the relation between the controlling PoC function, participating PoC function and the PoC Client in multiple network environment for a PoC group session.

Figure 4.1.1.2.4: Relationship between the controlling PoC function,
participating PoC function and PoC Clients for PoC group session

4.2 PoC offline charging architecture

Figure 4.2 depicts the PoC offline charging architecture, as described in TR 23.979 [200].

Figure 4.2: Charging architecture for PoC offline charging

As described in TS 32.240 [1], the PoC Server contains an integrated CTF that generates charging events and forwards them to the CDF. The CDF, in turn, generates CDRs which are then transferred to the CGF. Finally, the CGF creates CDR files and forwards them to the Billing Domain (BD). The possible mapping onto physical components and interfaces for the charging functions is described in TS 32.240 [1].

4.3 PoC online charging architecture

Figure 4.3 depicts the PoC online charging architecture, as described in TR 23.979 [200].

Figure 4.3: Charging architecture for PoC online charging

When PoC Server fulfils the controlling PoC function, then it provides centralized charging reports. When it fulfils the participant PoC function, then it provides the participant charging reports. For online charging, the PoC Server uses the Ro interface and application towards the OCS as specified in TS 32.299 [50].
The OCS considers and treats controlling PoC Server online charging reports and participant PoC Server online charging reports as independent reports (independent events if IEC is used or independent sessions if charging is SCUR based).