Demand Priority

Demand Priority

Demand priority is an access method used with the new 100 Mbps 100VG-AnyLAN standard. Although demand priority is officially considered a contention-based access method, demand priority is considerably different from the basic CSMA/CD Ethernet. In demand priority, network nodes are connected to hubs, and those hubs are connected to other hubs. Contention, therefore, occurs at the hub. (100VG-AnyLAN cables can actually send and receive data at the same time.) Demand priority provides a mechanism for prioritizing data types. If contention occurs, data with a higher priority takes precedence.

100VG-AnyLAN cabling uses four twisted-pairs in a scheme called quartet signaling.