Allied Telesis AT-S25 - Manual (Page 163)

AT-S25 Management Software User’s Guide
163
Class of Service Overview
The AT-8316F or AT-8324 Switch supports CoS as specified in the IEEE
802.1p and 802.1Q standards. CoS can be important in network
environments where there are time-critical applications, such as voice
transmission or video conferencing, that can be adversely affected by
packet transfer delays.
Prior to CoS, network traffic was handled in a best-effort manner. File
transfer delays did occur, but were mostly transparent to network users.
But with the introduction of time-critical applications, packet transfer
delays can prove problematic. For example, transfer delays of voice
transmission can result in poor audio quality.
CoS was designed to address this problem. The 802.1p standard outlines
eight levels of priority, 0 to 7, with 0 the lowest priority and 7 the highest.
The AT-8316F or AT-8324 Switch has two priority queues, low and high.
When a tagged packet enters a switch port, the switch responds by
placing the packet into one of the two queues according to following
assignments:
For example, a tagged packet with a priority tag of 6 is placed in the high
priority queue, while a packet with a priority tag of 1 is placed in the low
priority queue.
These priority-to-queue assignments can be overridden using the
AT-S25 management software on a per port basis.
IEEE 802.1p AT-8316F or AT-8324 Switch
Priority Levels Queue
7
6
5
4
3
2
1 high
high
high
high
low
low
low
low