The VB5 interface

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The VB5 interface is an ATM-based broadband interface at the ‘V’ reference point, the interface between a user access and a service node (SN), also known as the SNI (service node interface) within the ITU-T. The B-ISDN architectural model allows for a number of different user accesses, such as straightforward digital sections and simple multiplexers, but it is anticipated that the most frequent implementation, particularly for mass deployment, will be via a broadband access network (AN) with VB5 interfaces.

The VB5 interface is specified in a similar way to its narrowband cousin V5, in two variants – VB5.1, which supports allocation of resources via the management system, and VB5.2, which adds a mechanism for allocating AN resources under the control of the SN, enabling call-by-call concentration in the AN. This paper describes the background to the development of VB5 and explains the two variants VB5.1 and VB5.2.

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