The present document describes the architecture and functionality required to support enterprise and corporate services as IMS applications hosted in the NGN operator's network on behalf of an enterprise (Hosted Enterprise Services). The present document also specifies the protocol requirements for the UE to attach to the NGN (in particular the IMS) and also any protocol requirements related to application servers provided in support of hosted enterprise services.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

Hosted Enterprise Services (HES) refers to a solution where an NGN hosts all business communication capabilities to a set of endpoints connected to a plurality of access points to this network. This type of network solution is also known as IP Centrex. In the simplest configuration all endpoints are connected to a TISPAN NGN IP-CAN. Endpoints may be SIP phones or legacy phones (Analogue or ISDN) connected to a gateway. All services by HES are provided by application servers using standard IMS procedures. User may access services that are specific to the enterprise they belong to as well as services available to any other IMS users. In more complex configurations some of the endpoints may be connected to a 3GPP IPCAN and/or a circuit-switched network, which is itself connected to the IMS via an MGCF. Endpoints connected to heterogeneous access networks may be served by the same HES. Endpoints served by a HES shall have the ability to setup a session, identifying the communication target by:

• a SIP URI of the form user @domain;
• an E.164 telephone number;
• a number within a private numbering plan;
• local service numbers.

With regard to supplementary services, HES have strong similarities with the provision of PSTN/ISDN simulation services, although the actual set of services may be different. Examples of services that are enabled by the architecture described in the present document are:

• All commonly used PSTN/ISDN services.
• IMS Multimedia Messaging, Presence and Conferencing services.
• Personal and Corporate Directory.
• Unified Voice mail.
• Operator assisted communications.
• Hot Line Calling.
• Abbreviate dialling.
• Line Hunting.
• Attended Communication Transfer.
• Blind Communication Transfer.
• Communication Pickup.
• Manager/Secretary filtering.
• Click to Dial.
• Colour Ring Back Tone.

The sole purpose of the above list of services is to illustrate the type of services that are enabled by the architecture described in the present document. This list is not intended to be exhaustive nor is it expected that all implementations will support all of these services. The list actual of enterprise services hosted in a network is a matter for each operator to decide.