A communication system capable of reliably recovering its communication functions on its own when a fault occurs, and which can be used to construct a highly flexible network. This communication system is configured so that a plurality of node devices (12) supporting data generating sources are connected via communication paths (13) that use ATM technology to a plurality of center devices (11), just as if it possessed distributed ATM switch functions. When the communication paths (13) between two (2) node devices (12-2 and 12-3) are cut, the center device (11-2) detects the fault point, and autonomously recovers communication functions by transferring the node device (12-2) originally under its control to the control of the center device (11-1). When this happens, the center device 11-2) cannot communicate via the communication paths (13) due to the fault, and must use a local communication means such as a wide area network (16) to communicate with the center device (11-1).

Hierarchical star or rooted tree networks have been implemented and have any desirable characteristics, including excellent performance, conceptual simplicity, and suitability for optical fiber implementations. However, they have a single point of vulnerability to catastrophic failure (the master or root hub) as well as vulnerabilities to single failures of links or hubs high in the hierarchy, which could disable large portions of the network. Redundant network components are added to eliminate this vulnerability and to make an economic but extremely robust and fault-tolerant network, while preserving the advantages of previous hierarchical networks.

An apparatus and method for secure and private communications in a triple-connected processor network. Communication of a message over at least three data paths is achieved by transmitting the message in coded form over the data paths, determining whether the message is correctly received, and if the message is not correctly received, identifying a non-faulty data path, testing remaining data paths to identify a faulty data path, and transmitting the message in coded form over remaining non-faulty data paths.

A connecting unit for use in a system comprising a `stack` of network communication units having a cascade connection has three ports having lines for forwarding and receiving data packets and for forwarding and receiving control messages. The connecting unit increments a first signal value defining an identification number received by way of a control message at a first port, provides the received signal value by way of a control message to the third port and provides the incremented signal value by way of a control message to the second port. The connecting unit also receives a second signal value defining an active unit count by way of a control message at the first port and provides the second signal value, incremented or not in dependence on a control message received at the third port, in a control message at the second port. The first signal values (UnitIDs) are used to establish the numbering of the units in the stack and the second signal values are used to compute a count of the `active` units in the stack.

A bypass mechanism is described for improving the operation of a daisy chain line linking a plurality of units and used for propagating a signal which may be trapped by the first unit in the chain having a pending service request to be serviced by a common resource 12. The daisy chain line is connected to each units through an input line and the signal to be propaagated, if not trapped by the unit is sent to the next unit through an output line. All units in the chain are connected to a bypass line. A plurality of bypass lines may be provided when a plurality of sets of consecutive units should be able to be disconnected from the chain. When it is desired to disconnect consecutive units from the chain, gating logic in the unit preceding the first unit to be disconnected causes the signal to be propagated to be provided to a bypass out line and, in the unit following the last unit to be disconnected, the signal taken from bypass in line signals which are sent to the units through bus 14.