Abstract: A communication network consists of end units (EUs) and distribution units (DUs) coupled together by links which may include local area networks (LANs). The units maintain neighbor tables by sending out Hello messages which indicate the unit type and contain the network service access point (NSAP) IDs or addresses of the units. Data messages (packets) mainly originate and end at EUs. An EU maintains only partial routing information about neighbors, while the DUs collectively maintain complete information about all NSAPs. So if an EU wants to send a packet to an EU which is not a neighbour (and sometimes even if it is), it need merely send it to a neighboring DU; that DU, along with the other DUs, must find a route to the destination EU. This invention provides a hybrid unit (HU), which acts as a DU to EUs but as an EU to DUs. The HU provides DU-like message forwarding but only on a local basis within a subnetwork of EUs and HUs.

Abstract: Process for making computer-aided drawings for applications such as computer-aided engineering (CAE) and computer-aided design (CAD). A drawing is made in the form of a planar map in all steps of its implementation, and the process proceeds iteratively with insertion, erasure, or coloring operations as the drawing is made.

Abstract: A node operating in a network using the International Standard Organization (ISO) High-Level Data Link Control (HDLC) network protocol includes a mechanism for encoding information such that frames including the encoded information can be correctly interpreted by nodes operating in either of the standard 16-bit or 32-bit ISO-HDLC operating modes. The encoding mechanism produces a preliminary frame check sequence by encoding the information in an encoder using a generator polynomial G.sub.48 (x), which is a combination of the generator polynomials G.sub.16 (x) and G.sub.32 (x) which are used to produce frame check sequences for nodes operating in 16-bit or 32-bit modes, respectively. Before the information is encoded, the encoding mechanism sets the encoder to an initial condition using an initializing polynomial I.sub.48 (x). The preliminary frame check sequence is further encoded by adding to it a complementing polynomial C.sub.48 (x). The result is a 48-bit frame check sequence.

Abstract: A message switching network is disclosed which consists of end units between which messages flow. The end units are coupled together directly (via LANs) or via common switching nodes through level 0 links; the nodes are coupled together via level 1 links; and the nodes are grouped into areas which are coupled together via level 2 links. A message entering a node has its destination area code compared with the node's area code, and an area/port table or an end unit/port table is used to look up the output port which is coupled to the end unit, next node in the area, or next area to which that message is to be delivered. Logic circuitry determines the incoming and outgoing levels, and a transition between levels is logged together with certain details of the message. Messages are thus monitored--i.e., their passage is recorded--when they cross levels in the hierarchy.

Abstract: A method and apparatus for improving the performance of the transferring of transaction handshakes between sections of synchronous logic which are in different timing domains providing immunity from set-up and hold violations and associated problems of metastability, by reducing the time overhead required for signal synchronization.

Abstract: A method and apparatus is disclosed for producing comparative data in a visually assimilable form. The method comprises providing a substrate which is divided into visually distinct zones each representative of a different area of comparison, providing first means over said substrate aligned with at least one said zone and visually indicative of first data relative to said at least one zone, and providing second means over said first means aligned with at least one said zone and visually indicative of second data relevant to said at least one zone, said second means being visually different to said first means. Said first and second means where they coincide in a said zone combine to provide third means visually different to said first and second means, whereby to provide an immediate visual comparison between the data represented by said first and second means for each of said zones.