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Community Member

QOS on school LAN

Hi all, I hope I'm posting to the right place, sorry if I should have used IP Telephony!

My question is this:

Our LAN consists of a Cisco 3560G L3 and 7 x Cisco 2960 L2. These provide a gigabit backbone. Off of these switches hang DLink unmanged switches to provide classroom network access. Our telephone provider is updating our system and providing an ip phone solution on top of the standard system. Our LAN is only using the default VLAN.

I understand that I need to create a class-map and policy-map but am not sure about exact settings. The IP phones will not be Cisco's (Siemens) but I'm assuming they will tag an IP prescedence 5.

I've never had to deal with QOS before and wondered if someone could give some advice on a general setup including Cisco commands to get a basic QOS setup running. This would include the class, policy, bandwidth etc. If you are able to help could you also explain the steps so that I can understand what I'm doing.

Gavin McKay

Community Member

Re: QOS on school LAN

Check out CISCO auto qos, since your core gear is CISCO and the rest unmanged this could work for you.

Here is a Q&A link:

Re: QOS on school LAN


A great place to start would be the Cisco QoS Enterprise Design Guide

This guide uses the approach described below

A successful QoS deployment is comprised of multiple phases, including:

1. Strategically defining the business objectives to be achieved via QoS.

2. Analyzing the service-level requirements of the various traffic classes to be provisioned for.

3. Designing and testing QoS policies prior to production-network rollout.

4. Rolling out the tested QoS designs to the production network.

5. Monitoring service levels to ensure that the QoS objectives are being met.

I have used this approach successfully for a number of customers and it is very effective.

I do not think Auto-Qos would be a good option for you as it is designed to support Cisco voice and can depend on Cisco proprietry features such as Cisco Discovery Protocol (CDP).

Given your environment you may benefit greatly from Cisco's recommendation to provision a "Scavenger" class that receives a very constrained amount of bandwidth and can be used to effectively control apps such as BitTorrent, Gaming etc.

The link below may help you re. the Siemens telephones

It states that they use DSCP EF for voice traffic and AF31 for call signalling. This is similar to Cisco although Cisco now use CS3 rather than AF31 for signalling (I would check with your Siemens supplier that the QoS info is up to date).

Hope this helps.

Community Member

Re: QOS on school LAN

were are these phones situated? if they are connected to the dlink unmanaged switches you will have a problem as all the data and voice will be using the same vlan thus not allowing you to have qos, i would also strongly suggest implementing more vlans ( for security and to brack up your network and broadcasts)

also if you are going to be using the dlink switches you will have a problem with trunk ports, as in most places the phone and computer use the same port to connect thus needing a trunk port as the voce and data use diffrent vlans. on unmanaged dlinks you cant do trunk ports.

Community Member

Re: QOS on school LAN

Thanks for the help everyone. I'll look into your   Cisco QoS Enterprise Design Guide James as this could help me to get things straight in my head!!

At present we do not have any problems with Trunk Ports as effectively the Cisco switches don't pay any attention to the DLinks. They just pass data through. I'm under the impression that if the Siemens phones set a DSCP tag then this will just pass through the Dlinks before the Ciscos acctually see the Tag and apply QOS. Therefore the only QOS being applied would be throught the Cisco Backbone. Is this theoretically correct?

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