Variation Fluctuation Smoothing for ATM Circuit Emulation Service

Circuit Emulation Service (CES) o ers backward compatibility between Asynchronous Transfer Mode (ATM) technology and the existing circuit-switched telephony services. However, meeting its quality of service requirements is not trivial. The cell transfer delay (CTD) of a connection should be controlled to be no larger than the delay in legacy circuit-switched networks, which usually imposes a constraint on the play-out bu er size at the receiver end. Therefore the end-to-end cell delay variation (CDV) has to be minimized to avoid either over ow or under ow of the small play-out bu er. To optimize the CDV performance for ATM CES service, we propose a new multiplexor scheduling scheme called Variation Fluctuation Smoothing (VFS). VFS estimates the clock of each connection by on-line tra c measurement. It then calculates the lateness of the head-of-line cell for each connection and assigns the highest priority to the latest cell. By attempting to match cell departures to a virtual clock, VFS resolves the root cause for CDV and optimizes the CDV performance for ATM CES. The VFS scheme has little computational overhead and requires only a few memory locations per CES connection. In simulation, VFS consistently out-performs the FIFO discipline under both transient and steady state tra c conditions.