demand priority (DP)

Demand priority( DP) is used as an access method for100Base- VG. The demand priority method is a polling mode in which a repeater polls the individual end devices for transmission requests.

In the demand-priority method, each end device signals its transmission request to the repeater with a priority identifier (low or high). The transmission rights are distributed within the priority classes according to a round-robin procedure. Since the allocation of the transmission rights lies with the repeater, it can provide guaranteed transmission bandwidth for time-critical applications such as interactive video/ audio applications. This means that the transmission medium can be utilized to almost 100% capacity.

The repeater can be cascaded so that larger networks can be built. The repeater knows the two working modes Privacy Mode and Promiscuous Mode. In Privacy Mode, the data packets are only sent to the addressee; this mode is used by the terminal devices, so that only the data packets for the respective receiver arrive at a terminal port. In Promiscuous Mode, on the other hand, the data packets are sent to all; this operating mode is used between repeaters, as well as for bridges and protocol analyzers.