User's Manual

C HAPTER 1 | Introduction
Overview
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IEEE 802.1P QOS
The SMCFS1601 and SMCFS2401switches support 802.1p priority queuing
Quality of Service, which is an implementation of the IEEE 802.1p standard.
With the 802.1p QoS function, network traffic that requires high priority, such as
VoIP (Voice-over Internet Protocol), web browsing applications or video
conferencing, can be forwarded before other traffic. The switches have separate
hardware queues for each physical port, when packets are received with an
802.1p priority tag, they are sent to the appropriate output queue.
The illustration below shows how 802.1p priority queuing is implemented on the
switches.
Figure 1: Mapping QoS on the Switch
There are four priority levels labeled TC0, TC1, TC2 and TC3. The untagged
packets and the eight IEEE 802.1p priority tags (defined by the standard) are
mapped to the four priority queues on the switch. TC3 has the highest priority of
the four priority queues while TC0 has the lowest priority. The untagged packets
and eight priority tags, specified in IEEE 802.1p, are mapped to the switch’s
priority tags as follows:
◆ Untagged packets, and packets with priority tag 1 and 2 are assigned to the
switch’s TC0 level queue.
◆ Packets with priority tag 0 and 3 are assigned to the switch’s TC1 level
queue.
◆ Packets with priority tag 4 and 5 are assigned to the switch’s TC2 level
queue.
◆ Packets with priority tag 6 and 7 are assigned to the switch’s TC3 level
queue.
Tag untag 0 1 2 3 4 5 6 7
Priority Level
Weight Value 1 2 4 8
TC0 TC1 TC2 TC3