Qos Overview; Qos Markers; Creating A Qos Policy - Symbol ES3000 Manual

8-2 ES3000 Advanced Concept Guide

8.1 QoS Overview

The ES3000 implements IEEE 802.1p Quality of Service (QoS) processing. QoS policies examine
packets and classify them. The classification is used to drop packets or to remark packets. The
possible markers are Class of Service (CoS) Priority, Type of Service (ToS) Precedence, and
Differentiated Services Code Points (DSCP). For each port, the outgoing packets are then placed in
four output queues based on CoS priority. The queues are serviced using a strict queueing algorithm.
See Configuring QoS Queues on page 8-11

8.1.1 QoS Markers

Two of the settable markers, ToS Prececedence, and DSCP, are not independent. The DSCP are
encoded in the top six bits of the ToS. The ToS Precedence is encoded in the top three bits of the ToS,
as shown below:
The COS priority is encoded in a different location, in first three bits of the Tag Control Infomation
(TCI) field of the 802.1p tag in the Ethernet frame.

8.2 Creating a QoS Policy

A QoS policy consists of a classifier, one or more actions, a port list and a sequence number. The
classifier determines which packets are affected by the policy. The action determines what is done
with the policy. The policy applies only to the traffic coming over the ports in its port list. Policies are
applied in sequence order.
There are three types of actions: in-profile actions, out-profile actions, and no-match actions.
• In-profile actions effect packets that are in-bound to the switch, ingress packets. In-profile
actions can either drop a packet or mark it with a DSCP value, CoS priority, or a ToS
precedence.
• Out-profile actions effect packets that match the characteristics specified by the classifier
and which exceed bandwidth or burst size limits specified in the out-profile. The actions can
be either to drop the packet or to change its DSCP value, usually to drop the DSCP value.
for details on the algorithm.
ToS
DSCP
ToS Precedence