5 Architecture

24.5243GPPArchitecture, functional description and signallingHosted enterprise servicesRelease 17TS

5.1 Functional Architecture

5.1.1 Overview

The functional architecture for supporting access to Hosted Enterprise Services is illustrated in figure 1. This functional architecture supports access from both SIP based endpoints and legacy endpoints.

The functional architecture for supporting access to Hosted Enterprise Services from both types of endpoints is obtained by a combination of the Core IMS Architecture defined in ETSI ES 282 007 [2] with the addition of an AGCF as defined in ETSI TS 182 012 [3] and ETSI ES 282 002 [12]. This should not be understood as an integration of an AGCF into the functional architecture defined in ETSI ES 282 007 [2]. The AGCF only applies to configurations where an H.248-controlled media gateway is required in support of legacy endpoints.

Figure 1: Functional architecture overview

All functional entities behave as defined in ETSI ES 282 007 [2], ETSI TS 182 012 [3] and/or ETSI ES 282 002 [12].

The service logic of the HES resides in one or more application servers. All sessions to/from a member of a HES shall be handled by at least one application server.

The service logic of the HES can be provided by the home network operator, or can be provided by a third party service provider. It is also possible that the enterprise itself provides the services, by providing equipment that acts as an application server beyond an ISC gateway function.

SIP-based endpoints may be connected to the IMS via any IP¨CAN valid for the current specification release. A HES may serve endpoints connected through both types of IP-CANs.

Legacy endpoints may be connected via a media gateway or a SIP-based Voice over IP Gateway (VGW). Both types of gateways may be part of the User Equipment (UE) or reside in the TISPAN IP-CAN. A SIP-based Voice over IP Gateway (VGW) plays the role of a UE with regards to the P-CSCF. A media gateway is controlled by the AGCF, which plays the combined role of a UE and a P-CSCF with regards to other CSCFs of the IMS.

ETSI TS 182 012 [3] provides a more detailed specification of the procedures that a VGW and AGCF shall support for enabling access to IMS-supported services from legacy endpoints.

NOTE: The concepts of "Media Gateway" and AGCF are defined in both ETSI TS 182 012 [3] and ETSI ES 282 002 [12]. A Media Gateway implements the R-MGF or A-MGF functional entities defined in ETSI ES 282 001 [1]. ETSI ES 282 002 [12] uses different names to refer to a Media Gateway depending on its location: a media gateway located in the customer premises is referred to as a Residential Gateway (RG) while a media gateway located in the IP-CAN is referred to as an Analogue Gateway Function (AGF).

5.1.2 Involved functional entities – originating session

Figure 2 shows the functional entities involved in an originating session.

Figure 2: Functional entities involved in originating sessions

NOTE: Figure 2 does not show the intermediate functions between the P-CSCF and the S-CSCF, or those between the S-CSCF and the terminating side.

The originating side can interoperate with any other terminating side scenario.

5.1.3 Involved functional entities – terminating session

Figure 3 shows the functional entities involved in a terminating session.

Figure 3: Functional entities involved in terminating sessions

NOTE: Figure 3 does not show the intermediate functions between the P-CSCF and the S-CSCF, or those between the S-CSCF and the originating side.

The terminating side can interoperate with any other originating side scenario.

5.2 Architecture involving heterogeneous core networks

A HES can serve a set of endpoints some of which being connected to the IMS and some others being connected to Circuit-Switched (CS) networks. Example scenarios are shown in annex B.