For the purpose of the present document, the terms and definitions given in TS 22.519 apply:

For the purposes of the present document, the following abbreviations apply: API AS ASP BGCF CN CND CNG DHCP FQDN HES HSS IBCF I-CSCF IM IMCN IMS IOI IP IWF MACF NASS NAT NGCN NGN P-CSCF PNP PSAP RACS S-CSCF SIP SSP TE TSP UE URI

A number of different scenarios will likely exist for enabling interactions between Next-Generation Corporate Networks (NGCN) and Next Generation (public) Networks (NGN). The present document describes a sub-set of these scenarios and the architectural and functional requirements that arise from the support of these scenarios. Future releases may document other scenarios as requirements emerge.

The development of different interaction scenarios based upon the distribution of the hosting of private network capabilities in the enterprise operator and/or in the public NGN operator leads to the concept of the public NGN operator being able to offer services to NGCNs and the NGCN users at a number of different levels. This concept is further described in ETSI TR 102 478 [8]. The most basic level of service provision is IP connectivity. Differentiation from the Internet can be in the form of improved or guaranteed quality of service or security. For the purposes of the present document an NGN that provides this level of service acts as a Transport Service Provider (TSP). A second level of service provision is in session establishment and control of communication sessions, e.g. voice, multimedia, messaging. Here the NGN adds value by being involved in the signalling protocol used to establish and control media sessions. For the purposes of the present document the primary session control signalling protocol concerned is assumed to be the Session Initiation Protocol (SIP). Added value can include intelligent routing, provision of quality of service for media, provision of gateway services to legacy networks, assistance in NAT traversal, etc. For the purposes of the present document an NGN that provides this level of service is known as a Session Service Provider (SSP). A third level of service provision is at the application level. Applications can be many and varied, but for the purposes of the present document an application is assumed to be applied on top of session level services. An application may be able to monitor or control multi-media sessions (either directly or through a protocol or API) and may or may not be involved in media as well. Examples of applications that involve media include conferencing services, transcoding and translation services and call distribution centres. Examples of applications that monitor or control sessions but do not involve media include presence services, call logging services and UA configuration services. In addition, an application may be accessed through a session control protocol such as SIP. For the purposes of the present document an NGN that provides this level of service is known as an Application Service Provider (ASP). At the application level, the additional services 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. An NGN may provide services at one or more of these levels. Not all services offered will be of interest to enterprise customers and of relevance for interworking with NGCNs. Enterprise customers may use different NGNs for different levels of service provision and may have different contractual relationships with each of these NGNs. In addition, for a given communication and depending on the number of parties to be interconnected and/or the number of services to be accessed, multiple providers may be involved. The scenarios provided in the present document are presented in accordance with this concept.

The present document has been structured following the service level categories as introduced in subclause 4.2 in mind, as follows:

• clause 6 presents scenarios that relate to provision of IP connectivity level services offered by an NGN;
• clause 7 presents scenarios that relate to provision of session establishment and control of communication session services offered by an NGN;
• clause 8 presents scenarios that relate to provision of application level services offered by an NGN; and
• clause 9 presents scenarios that relate to provision of session level roaming services offered by an NGN.

The scenarios presented in clause 6 are IP level virtual leased line services between NGCN sites or between an NGCN site and a remote NGCN UE. The scenario presented in clause 7 is a session level virtual leased line. The application level service scenarios presented in clause 8 are hosted enterprise services (HES), subscription based business trunking and peering based business trunking. Clause 9 presents a special class of session level service scenarios that are so distinct from other session level services that they are a service class of their own. Roaming scenario covered in this release is the ability for an NGCN user to be able to roam into an NGN with which the NGCN has a roaming agreement. Other scenarios are listed for completeness, however these scenarios are not in the scope of the current release or are already covered as part of normal roaming procedures.