Abstract: An edge switch for an Ethernet network maintains look-up tables of media access control addresses and network addresses for local sources and destinations at least two sub-nets, so that it can forward packets directly even when the local source and destination are on different sub-nets and forwards packets to a core router when the destination is not local to the edge switch.

Abstract: A classification search engine for the application of classification rules to a data packet comprises a rules engine for applying a succession of rules, each rule including an operating code. At least some rules are each a single rule of which the operating code specifies a respective portion of the packet, such as a longword, for the extraction of data for the application of the respective rule. Each single rule includes a mask field for controlling the application of the single rule to the data. Other rules are multiple rules of which the operating codes identifies the rule as a multiple rule and which includes a mask for controlling the application of the multiple rule to the results of the application of a multiplicity of single rules to the packet. The operating code for a single rule specifies a pre-determined packet type and a decoder will determine whether a packet conforms to this type (which may be specific or generic) before allowing the application of the rule to the packet.

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 packet memory system including a memory space having a multiplicity of addressable memory locations for the storage of data packets, pointer control means for generating a write pointer which progressively defines where data is to be written to the memory space and a read pointer which progressively defines where data is to be read from the memory space and an ageing clock which defines a succession of intervals. The pointer control means generates a ‘current’ pointer and a ‘discard’ pointer and for each interval is operative to cause the ‘current’ pointer to correspond to an immediately previous value of the write pointer and to cause the discard pointer to correspond to an immediately previous value of the said current pointer. In this manner the portion of the memory space between the ‘discard’ pointer and the read pointer denotes data which has been in said memory space for at least two of said intervals.

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: 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 data connection between two network stations such as an Ethernet hub and an end station which are both capable of exchanging data at the higher of two rates, the higher rate being selected by an auto-negotiation process, is monitored for the occurrence of error represented by a symbol representing the start of a data packet immediately followed by an idle symbol. The rate of occurrence of such errors is compared against a threshold and the speed of the data connection is downgraded to the lower rate.

Abstract: A method of controlling access to a common physical data transmission link from a multiplicity members of a packet-based local area network, wherein the members are partitioned into a plurality of virtual local area networks (VLANs) and wherein packets are identified according to the virtual local area network from which they come, comprises (a) monitoring packet traffic from the virtual local area networks on the link and thereby obtaining measures of the traffic flow from each of the virtual local area networks; (b) determining whether the traffic flow for each respective VLAN is above or below a threshold; (c) denoting a VLAN which is above its threshold as in a restricted state and denoting a VLAN which is below its threshold as in a priority state; (d) arbitrating between requests from the VLANs to transmit data packets on the link; and (e) according priority in the arbitration to a VLAN which is in a priority state over any VLAN which is in a restricted state.

Abstract: An extender for use in with a cascade stack of network devices comprises an electronic circuit which has three ports, and circuit connections coupling each of the three ports to each of the other two ports; port connectors for each port; a two-part housing of which a first part has an end wall apertured for the protrusion of a first and a second of the connectors and a second part has an end wall apertured for the protrusion of a third of the port connectors; and screw fixings for securing the housing parts together.

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 method for operating a multi-segment repeater hub wherein at least some of various signal ports connecting signaling stations to the hub can be connected selectively to different segments of the hub, comprising: monitoring signal traffic between the stations and the hub and thereby establishing a database which indicates for each of a plurality of ports the volume of signal traffic between the respective port and each other port in said plurality and any segment through which any of said signal traffic flows and to which a port other than a port in said plurality is connected, computing the traffic to and from the ports in said plurality and said segments and the traffic between the segments for each of a plurality of possible configurations in each of which a selected port is notionally moved from connection to one segment to connection with another segment; computing according to selected criteria a preferred set of connections to the ports to the segments, and switching the connections of the ports and s

Abstract: A search apparatus and method for establishing efficiently whether a particular number, eg a MAC address, is stored in a database, eg in a communications bridge. The search is conducted stepwise on the basis of portions of the number, until one or zero match is found in the database. In the event that one match is found, a final confirmation is made that the whole of the number located and the number searched for are the same. This provides an efficient way to search among a subset of possible very large numbers.

Abstract: A network device for use in a data communication network comprises: a multiplicity of ports capable of receiving input data; a common buffer memory for storing in respective buffers data received by the input ports; and processing system for controlling the writing of data into buffers and the reading of data from said buffers. The processing system determines whether the extent of occupation of the common buffer memory exceeds a threshold defined to represent congestion of the memory. Counter system enabled by the processing system on detection of the aforementioned threshold count units of input data through the respective ports, the processing system decrementing these counters as data is read out from the common buffer memory.

Abstract: Increasing the through-put rate of data processing in an electronic printer by accepting incoming data at a rate which varies inversely with the variable print density of the incoming data being received. The processing of non-printable or non-graphic characters, such as SPACE, associated with the performance of control functions is carried on at a higher rate than is the case for printable or graphic characters.