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Basic QoS for 4500G

Occasional Contributor

Basic QoS for 4500G

I have a situation with a stack of 8 4500G's where there are softphone users experiencing voice quality problems. There are no VLANs or QoS currently in place.

The softphones have an option to tag traffic as DSCP 46, which according to 3com documentation is "Expedited Forwarding (EF) class: In this class, packets can be forwarded regardless of link share of other traffic. The class is suitable for preferential services with low delay, low packet loss ratio, low jitter, and assured bandwidth"

My question is what needs to be enabled on the switches to do this?  (I doubt that DSCP priorization would just happen automatically without setting some sort of QoS.)

It appears that I need to:

 - set priority trust so that the DSCP packet priority level takes precedence over port priority

 - set SP or WFQ queue scheduling on each port

Does that seem accurate or am I missing something?  Do I need to setup ACL or VLANs in order to do this, or can I simply use the DSCP priority?
Super Advisor

Re: Basic QoS for 4500G

At first, create a voice VLAN:


name VOICE

Enable the voice VLAN:

voice vlan enable

Configure the ports as follows:

interface giga 1/0/N

port link-type hybrid

port hybrid vlan  tagged

priority trust enable

In the uplink ports,at both sides:

port link-type trunk

port trunk permit vlan 6

I assume that you are using the default VLAN 1 only.

This commands can help a little in order to increase the voice performance. But, at the other hand, I suggest you to take a look in QoS settings using the configuration guide, and create and assign ACLs in order to improve more efficiency to the traffic priorization.


This message was edited by Fred_Mancen on 5-24-10 @ 2:25 PM