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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
78-6511-05
Chapter 8 Configuring VLANs
Configuring 802.1p Class of Service
Port Scheduling
Each port on the switch has a single receive queue buffer (the ingress port) for
incoming traffic. When an untagged frame arrives, it is assigned the value of the
port as its port default priority. You assign this value by using the CLI or CMS
software. A tagged frame continues to use its assigned CoS value when it passes
through the ingress port.
CoS configures each transmit port (the egress port) with a normal-priority
transmit queue and a high-priority transmit queue, depending on the frame tag or
the port information.
Frames in the normal-priority queue are forwarded only after
frames in the high-priority queue are forwarded.
Table 8-12 shows the two categories of switch transmit queues.
Table 8-12 Transmit Queue Information
Transmit Queue Category
1
1. Catalyst 2900 XL switches with 4 MB of DRAM and the WS-X2914-XL and the WS-X2922-XL
modules only have one transmit queue and do not support QoS.
Transmit Queues
Catalyst 2900 XL switches,
Catalyst 2900 XL Ethernet
modules (802.1p user priority)
Frames with a priority value of 0 through 3 are
sent to a normal-priority queue.
Frames with a priority value of 4 through 7 are
sent to a high-priority queue.
Catalyst 3500 XL switches,
Gigabit Ethernet modules
(802.1p user priority)
Frames with a priority value of 0 through 3 are
sent to a normal-priority queue.
Frames with a priority value of 4 through 7 are
sent to a high-priority queue.
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