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Ethernet and QoS

Oct 28, 20021 min

Can an Ethernet network support quality of service?

Can Ethernet networks support quality of service?

Raw Ethernet networks do not provide quality of service (QoS) policy management controls directly.

Ethernet QoS policy management can be provided through LAN switching equipment by using certain extensions to the Ethernet standard. The 802.1Q Ethernet specification includes a tag, inserted into Ethernet frames, that defines virtual LAN membership. Three bits in this tag identify priority as defined by 802.1D (previously 802.1p) to provide for eight priority levels.

Switches and routers can use the tag to give traffic precedence by queuing outgoing frames in multiple buffers. 802.1D provides Differentiated-Services functionality for Ethernet segments. Diff-Serv is an IETF specification that works at the network layer by altering the IP type-of-service field to identify particular classes of service. Diff-Serv is a class-of-service management scheme rather than a true QoS implementation.

Other internetworking protocols available for supporting QoS are Resource Reservation Protocol, used to reserve end-to-end network resources for a particular network flow (in one direction); Real-Time Transport Protocol, which is optimized to deliver real-time data such as audio and video streams through multiplexed UDP links; IP Multicast; and Multi-protocol Label Switching.