The service provider provides QoS service level agreement (SLA) for the controlled-latency, controlled-load 1 (AF31), controlled-load 2 (AF21), and Best-Effort traffic classes. The service provider maps the enterprise customer QoS classifications into the four defined traffic classes of the service provider.
The service provider router recognizes the packet as a high-priority voice packet and assigns the packet to the real-time EF class. The packet is re-marked to DSCP = 46 to fit the service provider classification conventions and sent on its way as a member of the real-time class.
Note FIFO represents the queuing mechanism that is being used on the output interface of the service provider router.
In the service provider core network, the packet will move along with minimal delay using EF.
The key congestion avoidance technology, weighted random early detection (WRED), is used in the service provider network. WRED ensures that lower-priority packets are dropped to ensure that priority packets make their way quickly through the network.
Because the voice packet is marked as EF—the service provider real-time class—WRED should have no impact on the packet. QoS policy for the service provider should be not to drop voice packets so that WRED would not be applied to packets identified as "real time."
The packet will almost certainly not be dropped and will encounter minimal delay.
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