A method and apparatus is provided for automatic protection switching in a ring network by creating a protection domain having a control vlan and protected data vlans and designating a master node and transit nodes connected by a primary port and a secondary port. The master node blocks the secondary port for data vlan traffic until it detects a fault either by notice from a transit node or by polling. When a fault is detected, the master node unblocks the secondary port for data vlan traffic. When the fault is restored, the transit node temporarily blocks the restored port to data vlan traffic thereby preventing a loop. Each time the secondary port is blocked and unblocked, the forwarding databases on all the nodes are flushed.

Ethernet automatic protection switching

A multi-master digital computer system has a bus, a plurality of master devices connected to the bus, a plurality of slave devices connected to the bus, and a bus controller for arbitrating bus requests by the master devices and for granting the bus to a selected one of the plurality of the master devices. Each master device is capable of originating a bus cycle to transmit data to or receive data from a desired slave device. The bus controller grants the bus to a selected master device which enters an address master state and addresses the desired slave device. The selected master device is transferred to a bus master state where a data transfer to or from the slave device is initiated. The selected master device then transfers to a data master state unless the selected master device wants, and is permitted through an arbiter, to retain control of the bus. The bus controller grants a bus request to a requesting master device through to the arbiter. The requesting master device is transferred into the address master state while the selected master device is still in the data master state, thus performing a pipelining operation.

Multi-master bus arbitration system in which the address and data lines of the bus may be separately granted to individual masters

There is provided a method for congestion control and avoidance in computer networks, which method includes the steps of sensing network congestion (including both sensing and predicting possible future network congestion) and allowing a network node to transmit at least one basic data segment and thereafter to transmit additional data, the quantity of said additional data being a function of the basic data segment, wherein the size of the basic data segment is deteremined at least in part by the sensed network congestion. Prediction of possible future network congestion is possible, for example, by learning from a history of network load and/or by detecting an increase in the number of users or other indications. When possible future network congestion is predicted, the application of the methods and apparatus of the invention is operative to prevent the development of future congestion altogether or at least to limit the evolving severity level that such future congestion would have otherwise reached. Controlling the transmission rate of network nodes is an important technique to help prevent future congestion altogether and/or to limit the severity of such congestion. There is also provided an apparatus for congestion control and avoidance in computer networks.

Method and apparatus for packet network congestion avoidance and control

A computer aided dispatch system is provided for use in a trunked communication system. The system comprises at least a master file node and a plurality of user nodes. The master file node contains a data record for each subscriber on the trunked communication system. Each data record has a plurality of fields that may assume various values. Each dispatcher "attaches" to a particular value of at least one field in any of the data records. The master file node maintains the records for each subscriber and automatically transmits an updated record to each dispatcher attached to the subgroup in which the subscriber operates. In this way, dispatchers are continuously provided the latest subscriber status even though the responsibility for monitoring the status of a particular subscriber unit may dynamically pass from dispatcher to dispatcher.

Computer aided dispatch system

When a fault occurs on a data communication processor that controls data communication between information processors, all information processors connected to the data communication processor are notified of the occurrence of the fault, upon which the information processors automatically reset the data communications processors. A fault detector is provided in an interface controller in a data communications processor 101, a crossbar switch 108, and an arbitration controller 109. When a fault occurs, the fault processor in the interface controller is notified of the occurrence and the failed location by means of a broadcast signal. The fault processor notifies the information processor of the fault by means of an interrupt signal. The notified information processor instructs the data communications processor to reset each controller of the data communication processor for fault recovery.

Fault processing method and information processing system

A large number (e.g., 20 or more) independent processors are connected by a network that provides high data throughput (e.g., 64 megabits/second). The network has redundant data, arbitration, and status/control buses. The buses extend across a plurality of microstripline backplanes connected together by impedance-matched twisted-pair cables. Data is transmitted in packets, along with status signals that provide error detection information.

Interconnection network for multiple processors

A data communication network over which data handling devices can transmit and receive packets among themselves having a bus, a number of subnetworks (each having interfaces for connecting a number of devices to each subnetwork), a concentrator for connecting each interface to the bus, each concentrator having a transceiver for transmitting, to the bus and to devices connected to each subnetwork, packets originating from devices within a subnetwork (transmitted packets), and for receiving from the bus packets originating from other subnetworks (received packets), collision avoidance circuitry for monitoring transmission attempts by devices connected to the subnetwork, for detecting competing transmission attempts that would create a collision on the subnetwork, and, upon such detection, permitting a selected attempt to enter the subnetwork, while preventing other attempts from entering it, collision detection circuitry for monitoring the bus and preventing all attempted transmissions from entering the bus whenever a packet from another subnetwork is present on the bus. In another aspect the interface means and the concentrator means include a network interface unit and a further interface unit.

Local area data communication network

A data communication network (10) over which data handling devices (14) can transmit and receive packets among themselves has a bus (22), a number of subnetworks (12) leach having interfaces for connecting a number of devices to each subnetwork), a concentrator (20) for connecting each interface to the bus, each concentrator having a transceiver (110) for transmitting, to the bus and to devices connected to each subnetwork, packets originating from devices within a subnetwork (transmitted packets), and for receiving from the bus packets originating from other subnetworks (received packets), collision avoidance circuitry for monitoring transmission attempts by devices connected to the subnetwork, for detecting competing transmission attempts that would create a collision on the subnetwork, and, upon such detection, permitting a selected attempt to enter the subnetwork, while preventing other attempts from entering it, collision detection circuitry for monitoring the bus and preventing all attempted transmissions from entering the bus whenever a packet from another subnetwork is present on the bus, circuitry for generating a collision signal upon detecting competing transmission attempts, a network interface unit (NIU) (16) associated with each device to cause withdrawal of an attempted transmission by that device upon receipt of a collision signal, a transmit channel over which transmitted packets are transmitted to the bus, a receive channel over which received packets are transmitted to devices connected to each subnetwork, a station interface unit (SIU) (18) intermediate the NIU and concentrator, a first transmit connector over which transmitted packets pass from the NIU to the SIU, a receive connector over which received packets pass from the SIU to the NIU, a collision signal connector over which collision signals pass from the SIU to the NIU, a second transmit connector over which transmitted packets pass from the SIU to the transmit channel, a combined receive and collision signal connector over which collision signals pass from the concentrator to the SIU, and over which received packets pass from the receive channel to the SIU, and demultiplexing circuitry in the SIU for routing collision signals to the collision signal connector and received packets to the receive connector.

Daniel C. Scavezze

Papers

Interconnection network for multiple processors

Local area data communication network

Data communication network