Arbitration apparatus employing token ring for arbitrating between

Abstract

Arbitration apparatus is described for arbitrating between a number of jobs, for example for distributing message traffic over a data transmission network. The arbitration apparatus comprises an activity register containing a number of activity bits indicating which of a number of transmission jobs is currently active. The apparatus also includes a two-tier token ring arrangement comprising an outer ring and a number of inner rings. Each ring consists of a number of registers, holding a token which is passed cyclically around the ring. Each register has a bypass path which bypasses the register if a corresponding job or group of jobs is inactive. The positions of the tokens in the rings determines which job is to be scheduled next. Each ring also includes a keeper register for preserving the token if all the jobs are inactive.