Abstract: A method of diagnosing, in a network comprising two devices (A), (B) connectable by a link (20), which link may be a physical link such as a cable or may be a wireless link, the type of failure of the connection between the devices (referred to as “link failure”, although the failure may only be a partial failure such as lack of synchronization and may lie not in the link itself but in the one or both devices or the protocol used), said method comprising connecting the two devices together (for example, by physically connecting them or switching on the link between them), at least one (B) of the devices including a plurality of registers (23), each register being adapted to store data about one or more types of said failure, running an auto-negotiation sequence, detecting said failure and passing signals relating to that failure to the relevant register(s), interrogating the or each register, and determining the type of said failure.

Abstract: A stackable network unit which can form a ring with other units has a master mode in which it can place packets on the ring, so that they can be ultimately forwarded from other units, and a repeat mode in which it can make a request for transfer of mastership of the ring, inserting bits in a header of an arbitration packet. If a master unit has completed the transmission of a packet and, preferably, after the required inter-packet gap has elapsed, it has not yet received an arbitration header to permit the making of an arbitration decision it can transmit a subsequent packet. The header information of this packet indicates to the other units that this subsequent packet is part of a burst of packets and the other units should not set requests in the header of this packet because this packet would not be used for arbitration.

Abstract: A method of operating a network device in a communication system for the transmission of data packets which include network addresses identifying sources and destinations of data, the network device being capable of both bridging and routing decisions and including a forwarding database by means of which a packet including network address data can be forwarded to at least one port and thereby to at least one network path identified by a network address, and packets can be forwarded to at least one port in response to a media access control address. The method comprises establishing a data table which contains entries comprising a network address of an end station to which a packet is destined, a respective media access control address and an identification of at least one port to which the packet will be directed within the device. The table is accessed in response to network addresses and media access control addresses, whereby the same table can be used for both routing and bridging decisions.

Abstract: An application specific integrated circuit includes a multiplicity of operative circuit blocks. Disposed in at least one of the blocks is a multiplicity of selectively operative heater modules for providing localised heating within the block. The heater modules may comprise cyclic redundancy code generators each coupled to respond to a system clock, and each heater module may include a system clock divider providing a multiplicity of differently divided clock signals and means for selecting a clock signal for use by the module. The invention is useful in design variable testing to produce variation with temperature of the frequency of an intermittent timing error.

Abstract: A network switch comprises a first device which includes a store for data packets, a second device which includes a plurality of ports from which the packets may be transmitted, a plurality of temporary stores each associated with one of the ports, a data bus connecting the first device to the second device, a unit for maintaining a count of units of storage space in respect of each of the ports, a unit for incrementing the respective count on transmission of data from one of the stores, and a unit for decrementing the count in response to dispatch of data from the temporary store in the first device to the second device.

Abstract: A high speed link between chips and comprising a multiplicity of synchronous serial data channels includes an onboard detector for detecting an error rate for each channel. The transmitter and the receiver chips are configured in response to the detector to select the channel having the lowest error rate as the control channel and optionally to render at least the channel with the highest error rate inactive.

Abstract: A method of diagnosing, in a network comprising two devices (A), (B) connectable by a link (20), which link may be a physical link such as a cable or may be a wireless link the type of failure of the connection between the devices (referred to as “link failure”, although the failure may only be a partial failure such as lack of synchronization and may lie not in the link itself but in the one or both devices or the protocol used), said method comprising connecting the two devices together (for example, by physically connecting them or switching on the link between them), at least one (B) of the devices including a plurality of registers (23), each register being adapted to store data about one or more types of said failure, running an auto-negotiation sequence, detecting said failure and passing signals relating to that failure to the relevant register(s), interrogating the or each register, and determining the type of said failure.

Abstract: A plurality of serial data streams are transmitted on a corresponding plurality of lines at a common frequency in equal groups of symbols. A framing signal composed of groups of symbols corresponding in number to groups of data symbols is transmitted on an additional control line. Each group of symbols in the framing signal includes a majority of symbols capable of representing a first plurality of code words and a second plurality, substantially less than the first plurality, of valid code words, and a minority of symbols which constitute parity check symbols. Each of the valid code words consists of a first sub-group of similar symbols and a second plurality of similar symbols. For some of the valid code words the symbols in the first sub-group are similar to the symbols in the second sub-group. For other valid code words the symbols in the first sub-group are different from the symbols in the second sub-group.