Preliminary view of availability objectives for the broadband integrated services digital network (BISDN)

Preliminary availability objectives for a fiber-based broadband integrated services digital network (BISDN) are discussed. The objectives are based on outage performance of existing network elements in conjunction with proposed network architectures chosen as hypothetical reference connections. The phase in BISDN deployment that has broadband integrated access (BIA) based on SONET/ATM with voice, data, and video carried in ATM cells transported within the SONET payload until they reach the central office is discussed. It is shown that the overall network-level availability objective can be as good as 99.99%. To achieve this, the long-standing loop objective of 99.99% availability (53 min/yr unavailability) must be maintained. The potentially adverse effect on this objective of propagating some switching functions into the access (loop) portion is quantified