In an actual access arrangement some of the channels available across an ISDN user-networks physical interface,as defined in the applicable interface structure,may not be supported by the network.Some ISDN services will not require the full capacity of a B-channel; in those cases in which users require only such services,the access capability might be further reduced. The capability provided by those channels that are actually available for communication purposes,is referred to as the access capability provided through the interface.