scope:

The present document specifies the physical, procedural and protocol requirements for interfaces at the VB5.2 reference point between an Access Network (AN) and a Service Node (SN). The VB5.2 reference point provides flexible (provisioned) virtual path (VP) link allocation and flexible (provisioned) virtual channel (VC) link allocation (controlled by the Q3 interfaces) as well as on-demand VC link allocation controlled by the SN via the broadband bearer connection control (B-BCC) protocol. That is, the VB5.2 reference point is a superset of the VB5.1 reference point, enabling on-demand VC link allocation in the AN and across the VB5 reference point via the additional B-BCC function.

The following B-ISDN customer access types with the general user network interface (UNI) characteristics defined in ITU-T Recommendation I.432.1 [22] are supported:

a) B-ISDN accesses with a UNI at 155 520 kbit/s and 622 080 kbit/s according to ITU-T Recommendation I.432.2 [23], i.e.:

1) SDH based according to ETS 300 300 [5];

2) Cell based according to ETS 300 299 [4].

b) B-ISDN access with a PDH based UNI at 1 544 kbit/s and 2 048 kbit/s according to ITU-T Recommendation I.432.3 [24].

c) B-ISDN accesses with a UNI at 51 840 kbit/s or 25 600 kbit/s according to ITU-T Recommendations I.432.4 [25] and I.432.5 [26].

B-ISDN accesses with a UNI according to future ENs and/or ITU-T Recommendations may require additional functionality at the VB5.2 reference point.

In order to provide for a migration from narrowband to broadband access network and service node arrangements, narrowband access types as specified for:

- V5.1 interface according to ETS 300 324-1 [7]/ITU-T Recommendation G.964 [39]; and/or

- V5.2 interface according to ETS 300 347-1 [8]/ITU-T Recommendation G.965 [40],

are also supported according to the integration scenario given in ITU-T Recommendation G.902 [16], clause C.2.2, using a circuit emulation function for the transfer of circuit mode into ATM.

In addition to these B-ISDN and narrow-band customer access types, other non-B-ISDN access types are also supported.

Examples for such non-B-ISDN access types are given below:

a) access types supporting asymmetric/multimedia services, e.g. Video on Demand (if not part of B-ISDN access types);

b) access types supporting broadcast services (if not part of B-ISDN access types);

c) access types supporting LAN interconnect functionality (if not part of B-ISDN access types);

d) access types that can be supported via an ATM VP cross-connect.

The concept of Virtual User Ports (VUP), as described EN 301 005-1 [1], may be applied to enable any specific implementation.

In accordance with the principles of B-ISDN (as specified in ITU-T Recommendation I.121 [41]), remote access arrangements across interfaces at the VB5.2 reference point shall support switched, and (semi-) permanent point-to-point and point-to-multipoint connections. They provide on demand, reserved and permanent services of a mono- and/or multi-media type and of a connectionless or connection-oriented nature in a bi-directional or unidirectional configuration, as supported for direct access arrangements to service nodes.

Functions to support security management (refer to ITU-T Recommendation X.800 [46]) related to the customer access are beyond the scope of the present document. Such security management functions have no impact on the VB5.2 reference point.

The present document does not specify the implementation of the requirements within the AN and does not constrain any implementation alternative as long as the functionality at the interfaces at the VB5.2 reference point as specified in the present document is met. Furthermore, the present document does not require that an AN shall support all the customer access types listed above.

The present document is not intended to define any systems or equipment in, or connected to, an SN via interfaces at the VB5.2 reference point. Therefore only the characteristics of the interfaces at the VB5.2 reference point are described.