Abstract: In one embodiment, a method is described for detecting an operational failure between the network unit and an adjacent network unit in the stack; controlling the switching engine to redirect packets which would otherwise be sent from a particular port to the adjacent network unit to be forwarded from another port to be sent to a different network unit in the stack; and entering the switching engine into a bypass mode in response to control data indicating an operational failure between at least two other network units in the stack to cause packets to be forwarded without being re-directed by the switching engine.

Abstract: A network unit for use in a switching fabric includes multiple units collectively constituting a single network entity, each having ports for the reception and forwarding of data packets. The network unit has at least one fabric port for connection to a partner port on another one of the units by at least one link. The network unit is organized to send and receive via the at least one fabric port protocol packets which contain information on the path costs between said units in the fabric and to perform an algorithm to determine, on the basis of said information, routes for data packets within the fabric to other units of the fabric.

Abstract: In one embodiment, a method is described for detecting an operational failure between the network unit and an adjacent network unit in the stack; controlling the switching engine to redirect packets which would otherwise be sent from a particular port to the adjacent network unit to be forwarded from another port to be sent to a different network unit in the stack; and entering the switching engine into a bypass mode in response to control data indicating an operational failure between at least two other network units in the stack to cause packets to be forwarded without being re-directed by the switching engine.

Abstract: A method and processing device for controlling the communication of data associated with a user on a network 1 is described, in which the communication of data to and from a user is controlled according to user profile information. In a preferred embodiment, the user profile information is maintained in a database 9 accessible to processing devices 5 providing access to the network 1, and includes a volume allowance for a predetermined time period, a maximum transmission rate and current usage information for the user. Each time a user connects to the network 1, the method determines whether the user is within the volume allowance, and if so, permits access to the network 1. The communication of data is controlled according to the maximum transmission rate. The method may be implemented in software.

Abstract: A network unit for use in a switching fabric includes multiple units collectively constituting a single network entity, each having ports for the reception and forwarding of data packets. The network unit has at least one fabric port for connection to a partner port on another one of the units by at least one link. The network unit is organized to send and receive via the at least one fabric port protocol packets which contain information on the path costs between said units in the fabric and to perform an algorithm to determine, on the basis of said information, routes for data packets within the fabric to other units of the fabric.

Abstract: A network stack includes a plurality of network units each of which includes a multiplicity of ports for receiving and forwarding addressed data packets, at least two cascade ports and a switching engine for forwarding received packets to at least one port in accordance with address data in the packets and a cascade connection including, for each of two opposite directions around the stack, at least one unidirectional path for data packets composed of links each between a respective cascade port on a network unit and a corresponding cascade port on the next network unit.

Abstract: A network unit for use in a switching fabric includes multiple units collectively constituting a single network entity, each having ports for the reception and forwarding of data packets. The network unit has at least one fabric port for connection to a partner port on another one of the units by at least one link. The network unit is organized to send and receive via the at least one fabric port protocol packets which contain information on the path costs between said units in the fabric and to perform an algorithm to determine, on the basis of said information, routes for data packets within the fabric to other units of the fabric.

Abstract: A network unit for use in a switching fabric includes multiple units collectively constituting a single network entity, each having ports for the reception and forwarding of data packets. The network unit has at least one fabric port for connection to a partner port on another one of the units by at least one link. The network unit is organized to send and receive via the at least one fabric port protocol packets which contain information on the path costs between said units in the fabric and to perform an algorithm to determine, on the basis of said information, routes for data packets within the fabric to other units of the fabric.

Abstract: A network unit for use in a switching fabric stores for each network unit in the switching fabric a respective change identification number. In each unit this number is incremented on each change of state. The unit broadcasts protocol packets which indicates incremented change identification numbers; receives corresponding packets from the other units; and determines when the last change identification numbers in the table are the same for all the units. This allows a control based on whether all the units know that all the other units have been updated in response to all the changes of state in the fabric. The network unit can also participate in a routing algorithm, and particularly a shortest path algorithm, within a fabric that constitutes a single network entity.

Abstract: Network units such as switches for use in a cascaded stack are organised to provide a cascade connection in the form of a dual unidirectional connection so that, in its ordinary configuration, there is at least one and preferably more than one unidirectional ring for each direction around the cascade, each ring including a respective port on each unit. For each ring, each port on a unit is connected by a respective link to a corresponding port on the preceding unit and the following unit. The units provide a self-healing operation in the event of various kinds of operational failure. The self-healing operation includes loop-back of packets in units adjacent the failure and bypass of a packet switching process for other units. The units include control logic for passing control frames containing status information relating to the units and links between them and for co-operation with a CPU to control a switching engine to perform the self-healing operation in accordance with that status information.

Abstract: 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.

Abstract: Cascade control logic for use in a switch or other network unit that can be used in a cascaded stack can maintain normally a point-to-point half-duplex connection for control data with each of the next preceding and next succeeding units in the cascade. Each cascade logic device is organised so that for one direction, conveniently called the up direction, a device is a master and in the other direction the device is a slave in respect of the control path. A control device will generate master control frames in the up direction and deliver slave control frames in the down direction. The control device is organised so that in the absence of reception of valid control frames on a control link control data which would otherwise be sent out on that link is looped back within the control device. In this manner the control device can maintain under normal circumstances two virtual control channels which can ‘self-heal’ notwithstanding the failure or powering-down of a unit in the cascade.

Abstract: A system for providing power over data lines, particularly Ethernet data lines, comprises a network switch including a multiplicity of ports each of which is capable of supplying power in addition to data packets, a controllable power source which is coupled to said ports for supplying power thereto and a processor which is coupled to control the supply of power by the power source. The processor is programmed to guarantee the supply of power to selected ports and to allow or inhibit the supply of power to ports other than the selected ports, having regard to a specified limit on the supply of power by the controllable power source and the total guaranteed power to the selected ports.

Abstract: A packet-switched network system comprises a multiplicity of multi-port network units each of which has first and second ports and other ports and transmission links coupling the first and second ports of said unit in a closed ring. The first and second ports and transmission links support duplex transmission of Ethernet data packets. Each unit transmits from said first and second ports packets including selected information enabling on reception of a packet at any of the units a determination of a number of hops from unit to unit around said ring said packet has made. Each unit has a forwarding database and in response to the said selected information controls the transmission of said packets in two directions around said ring, and each unit causes discard of packets which have according to said selected information circumnavigated the ring.

Abstract: Traffic through a port of a network switch is monitored and controlled by a token bucket system having a duplex mode in which the bandwidths available for incoming and outgoing packets are controlled by a single token bucket and a half-duplex mode in which the bandwidths for incoming and outgoing packets are controlled by a respective one of two token buckets.

Abstract: A system for providing power over data lines, particularly Ethernet data lines, comprises a network switch including a multiplicity of ports each of which is capable of supplying power in addition to data packets, a controllable power source which is coupled to said ports for supplying power thereto and a processor which is coupled to control the supply of power by the power source. The processor is programmed to guarantee the supply of power to selected ports and to allow or inhibit the supply of power to ports other than the selected ports, having regard to a specified limit on the supply of power by the controllable power source and the total guaranteed power to the selected ports.

Abstract: A trunk connection to a stack of network switches is coupled to physical ports distributed among the switches. A switch has an internal logical port for a protocol engine. A packet received by way of the trunk at a port on a switch which does not host the protocol engine is sent over a cascade connection to the host switch with a tag that is interpreted within the host switch as if the packet cam from the logical port. The tagging and interpretation distinguishes between packets which might or might not be intended for the protocol engine and did not arrive by way of the trunk from packets which are intended for the protocol engine and have been received by way of the trunk.

Abstract: A network switch comprises a multiplicity of ports for receiving and forwarding addressed data packets, a forwarding engine for directing packets received at the ports to at least one other port, a register for storing unit identifications of a set of units including the network unit, and hashing logic for selecting one of the unit identifications in response to address data in a packet. The forwarding engine makes a determination whether the one of the unit identifications corresponds to the network unit and is operative to direct the packet in accordance with that determination. The use of the register enables a substantial increase in the number of ports that can be members of a stack-wide trunk.

Abstract: In a stack of network units each includes a multiplicity of ports for receiving and forwarding addressed data packets and a forwarding engine which in response to address data selects at least one port for the forwarding of a data packet. A cascade connects the units and allows the transmission of a packet placed on said cascade by a unit to all the other units. Each unit is responsive to a packet received from the cascade to forward or discard the received packet according to predetermined forwarding rules. A trunk includes a respective port of each of some but not necessarily all the units. Each unit includes a ‘trunk box member’ register indicating which of the units has at least one port connected in the trunk When a first unit in the stack receives, at a port connected neither to the trunk nor the cascade, a packet destined for the trunk, the first unit directs that packet to a port connected to the trunk if the first unit has such a port and otherwise sends that packet to the cascade.

Abstract: A stackable multi-port communication device for a packet-based data communication system, having a multiplicity of physical ports for the reception and dispatch of data in the form of packets, includes switch logic for selecting for a packet at least one destination selected from a multiplicity of ports which include a logical port common to a specified group of said physical ports. A cascade trunk logic, coupled to the switch logic, is used for determining, for the dispatch of a packet directed to said logical port, a selected port of said group of said physical ports; and a remote monitoring logic is used for forwarding a copy of the packet.