Asynchronous transmission mode (atm) handler

Abstract

An ATM handler that sets a switchover indication to a control register according to a system switchover order from a controller such that a switchover indication is supplied to a selector and line interfaces according to an output signal from the register. The setting of a switchover indication synchronize a switchover of an operation to count user cells between the line interfaces of the active and standby systems with a switchover of a stream of input cells to an ATM switch by a selector. A protection period is provided to allow a time after the system switchover according to a transmission delay lag. The line interface related to a delayed phase assigns a bit for stopping counting to cells input during the protection period so that the counting operation is conducted for the cells other than those assigned with the bit for stopping counting. As a result, duplicate of counting cells is prevented and the number of user cells are accurately counted.