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: A multiport repeater for a local area network installation has (in addition to its conventional functions) means for storing access rules for the items of equipment connected to it. It reads a portion of each frame, which may be all or part of the destination address segment and/or of the source address segment and/or of the control segment of each incoming data frame, or it could be a frame or protocol identifier incorporated in opening bytes of the data segment. It compares the data that it reads with the stored access rules to determine whether the frame is permitted or not. If not, the repeater modifies the frame which it is in the course of re-transmitting, for example by overwriting it with meaningless digits or by encrypting it. It may also report the source address, destination address and reason for deciding to modify the frame to the network controller.