Abstract: A facility is provided for operating an asynchronous packet transmit bus such that isochronous information packets may be transmitted from a source to a destination with a fixed, constant delay. The fixed, constant delay is achieved by employing a bandwidth management bus and assigning to port modules which contend for access to the transmit bus respective levels of priority, in which the highest level of priority is associated with isochronous information and in which lower levels of priority are associated with other types of information, such as asynchronous information. In addition, each port module which transmits isochronous information is assigned at least one time slot of each frame of time slots. In this way, a port module that needs to transmit isochronous information is granted access to the transmit bus during its assigned time slot if the module asserts such highest level of priority in response to its address being transmitted over the bandwidth management bus.

Abstract: A communications system that is arranged to transport so-called connection oriented messages via respective virtual circuit connections is enhanced so that it also transports so-called connectionless messages via a predefined virtual circuit connection that is common among those data modules which participate in the connectionless message service. In particular, each module which participates in the connectionless message service is assigned, in addition to a primary address that is used in conjunction with associated channels numbers to transport respective connection oriented messages, a common address and a channel number that is used solely for transporting connectionless messages. In this way, the communications system processes connectionless messages as though they were connection oriented messages.