Packet Priority (NDIS 5.1)
Note NDIS 5. x has been deprecated and is superseded by NDIS 6. x. For new NDIS driver development, see Network Drivers Starting with Windows Vista. For information about porting NDIS 5. x drivers to NDIS 6. x, see Porting NDIS 5.x Drivers to NDIS 6.0.Packet priority is a three-bit value that hubs and switches use to establish the priority of packets in shared-media 802 networks. Typically, when a network segment becomes congested, the hub-and-switch workload results in the delay or dropping of packets. On a network using packet-priority values, a packet with a higher priority receives preferential treatment and is serviced before a packet with a lower priority.
Operating system components that are aware of Quality of Service (QoS) provide priority information to transmit over the network. QoS-aware components derive this priority information by mapping service types to IEEE priority values. The Integrated Services Working Group (Intserv) of the Internet Engineering Task Force (IETF) defines this service-type mapping. The Intserv specification of these priority values, also called "user-priority" objects, can be located in the IETF Internet site.
To locate this specification (NDIS 5.1)
Go to the IETF Search Engine
Go to the Request for Comments (RFC) section by clicking RFC Pages.
Proceed to the Integrated Service Mappings on IEEE 802 Networks specification by entering RFC number 2815.
Note that IETF might supersede this specification with later drafts or the final specification. This specification describes prioritizing packets using IEEE priority values, whereas the IEEE 802.1Q standard describes how to actually mark packets for network priority. Either QoS-aware applications or QoS-aware operating system components that work on behalf of these applications can determine the intserv service types used for the mapping.
Unless a host computer has properly negotiated QoS with the network, the host computer should only mark packets transmitted with a "best effort" priority value. If the host computer has a Packet Scheduler installed, the host uses the appropriate QoS-signaling components to negotiate with the network for higher priority values.