QoS newbie

Greg Wrobel · ‎03-30-2011

Hi,

I never before did QoS on cisco switches, so I have to ask questions. I have 1x c3560G and 8x c2960 with 4 VLANs. Now, I need to prioritize traffic on the Voice VLAN (no cisco phones, so can't use cisco voice vlan). Would it be enough to configure just CoS value at 7 for every port where a phone is connected or do I need to configure policing or something else? I am really new to QoS so I need help.

Thanks

Eugene Lau · ‎03-30-2011

Hey Greg,

A starting point is here:

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSDesign.html

See if you can access the design guide for QoS (contact web-help@cisco.com if you have access issues). There's many ways of achieving a QoS strategy and it depends on the requirements.

Fundamentally, the devices simply need to recognise the priority and queue the traffic accordingly. If your IP phones already generate a QoS value (most do), you could simply trust the marking throughput your network.

As you have mentioned, you "can" mark all traffic from the phone as CoS7 and switches will queue accordingly. Typical practice for voice traffic is CoS5 or DSCP46. Sticking to typical or "best practices" means it's most likely a main stream solution that has been tried and tested .

Policing is not required unless you have bandwidth management requirements - such as potentially oversubscribing a WAN link

What kind of IP phones are you running and in which VLAN? (also mention the call manager device)

Are you intending to run converged voice and data? (eg. PC's connected to IP phones on the same wire)

What's the current port configuration?

HTH get you started

Eugene.

Greg Wrobel · ‎04-05-2011

What kind of IP phones are you running and in which VLAN? (also mention the call manager device)

Phones are not Cisco, otherwise I could just use cisco voice vlan. The phones are manufactured by German company called Snom (www.snom.com), and calls will be managed by their sip server with PSTN cards, so it will go digital than analog. Phones will run on VLAN3, whereas data will be on 2 and Test network on 4.

Are you intending to run converged voice and data? (eg. PC's connected to IP phones on the same wire)

I was thinking about it. Would it work if I just trust the CoS coming from phone and can I assume that if PC will not send CoS value it will be treated as the best effort? Anyway I have enough ports in most of the office that I would not need to do that, but it would come handy in others.

What's the current port configuration?

Currently, ports are configured with Cisco Voice Vlan, since I was playing around with. Network is not built yet. Everything is set up in one room with phones and computer connected to, For now it is my play ground, and I have about 2 months before it needs to be installed and operational.

I hope this answers the questions and shades some light on the situation.

Eugene Lau · ‎04-05-2011

Great stuff Greg,

For converged voice and data with 3rd party phone (SNOM) -

- static trunk port

- allowed voice and data vlan

- trust CoS (as you have stated)

In the Cisco world, QoS marking for the phone and PC can be configured on the call manager. This is the case with most 3rd party systems as well. As you deducted, the default for the data port on the phone would be typically CoS0 and queued on a best effort basis

Side note and not really relevant:

While Voice VLAN is used for Cisco IP phones on an access port and not functional on a static trunk port, I like to use it to identify the voice vlan in the config Makes the config easy for other engineers to understand when you look at the port config

Good luck!

Eugene.