The present document specifies network requirements: - to support connection and interoperation of business communication capabilities (either hosted in NGCN or NGN) to the NGN; and - to support connection and interoperation of business communication capabilities to other business communication capabilities (either hosted in NGCN or NGN); and - to support connection and interoperation of business communication capabilities to other business communication capabilities located in or connected to the ISDN and PSTN; and - to support PABX functionality (hosted enterprise services) in an NGN. NOTE 1: Network requirements to support connection of NGCN directly connected to an NGN are specified. NOTE 2: Attachment of legacy PBX functionality to the NGN is not specified in the present document. It is assumed that existing legacy service requirements apply in this case. The present document also specifies network requirements for communication between NGCN capabilities (including user equipment) to other NGCN capabilities of the same enterprise through the NGN (e.g. geographically separated). The present document does not specify NGCN services@ nor does it specify network based application services provided to a user of an NGCN.