Information technology - telecommunications and information exchange between systems - local and metropolitan area networks - specific requirements. Part 12: demand-priority access method, physical layer and repeater specifications

摘要

This international standard defines the protocol and compatible interconnection of data communication equipment via a repeater-controlled, star topology local area network (LAN) using the demand-priority access method. The purpose of this protocol is to provide a higher speed LAN with deterministic access, priority, and optional filtering. Pursuant to this, the protocol will (a) provide a minimum data rate of 100 Mb/s; (b) provide smooth migration from ISO/IEC 8802-3 and ISO/IEC 8802-5 LANs; (c) support either ISO/IEC 8802-3 or ISO/IEC 8802-5 frame format and MAC service interface to the LLC; (d) support a cascaded star topology over twisted pair and fibre-optic generic building wiring; (e) allow topologies of 2.5 km and greater with three levels of cascading; (f) provide a physical layer bit error rate (BER) of less than 10/sup -8/; (g) provide fair access and bounded latency; (h) provide two priority levels: normal and high; (i) provide a low-latency service through high priority for support of multimedia applications over extended networks; and (j) support an option for filtering individually addressed packets at the repeater to enhance privacy.