An overview of IEEE 802.12 demand priority

Demand priority is the media access control protocol used by the new 100 Mb/s 100 VG-AnyLAN network being standardised by the IEEE 802.12 committee. The network can interconnect hubs in multiple wiring closets (without bridging or routing), and can have a network diameter of several kilometers. The network is the only 100 Mb/s technology to support Category 3 cabling including bundled cables, which are found at many user's installations. Demand priority supports two priority levels, and this will enable it to effectively support real time multimedia applications. A further advantage of IEEE 802.12 demand priority is that it supports IEEE 802.3 and IEEE 802.5 frame formats, thus allowing users to evolve from the currently prevalent 802.3 and 802.5 networks without having to load new software. This paper describes demand priority, and compares it with other high speed local area network technologies.