COMMUNICATION NETWORKS

摘要

Communication Networks Fig. 1 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 neighbour tables by sending out Hello messages which indicate the unit type and contain the network service access point (NSAP) IDs or addres-ses 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 pocket to an EU which is not a neighbour (and sometimes even if it is), it need merely send it to a neighbouring 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. Figure 5