Mitel QOS with Cisco Switches

[sfernandes]

Hey All,

I know this may probably be a dead beaten topic, but I need to ask it anyways, mainly cause I have not dived into QOS and just want to ensure I do this right.

Basically we have two sites, connected to each other through an MPLS network by Telus. The Bandwidth on the MPLS is 100 MB.
As per usual during heavy usage the line gets saturated and we start getting loss of voice packets etc.

We are using a cisco layer 3 switch on each side of the MPLS to do our routing: 3750G. These are our core switches. Access layer switches connect to them which are simply layer two switches: 2960G switches.

On our layer two front: two make calls to one another within the same site we have no issues, so I can forgo QOS on this side for now.

What I need is to know which is the best / most straightforward method to prioritize the VOIP traffic on the Layer 3 front.

I can currently set the Priority to 6 and the DSCP value to 46 (I believe that is the expedited QUEUE) within mitel DHCP controller.

Overall I am imaging I will then have to do some sort of qos trusting, but does this come into play on the layer two front or layer 3 front.

I might be scattered a bit, so any guidance / sample code would be most welcome.

Thanks,

Steve

[acejavelin]

I am foggy on this stuff in the Cisco world, but it seems to me you need let the switches/routers know to "trust" the QoS tags put on the voice packets by the phones/Mitel or they will be ignored, "msl qos trust dscp" and "msl qos trust cos" seem to come to mind here but I can't seem to find my notes anywhere right now, but hopefully that might start you in the right direction.

[martyn]

I am foggy on this stuff in the Cisco world, but it seems to me you need let the switches/routers know to "trust" the QoS tags put on the voice packets by the phones/Mitel or they will be ignored, "msl qos trust dscp" and "msl qos trust cos" seem to come to mind here but I can't seem to find my notes anywhere right now, but hopefully that might start you in the right direction.

Yep those are the two commands you are after.

At 100MB though you would have to question how the link is being so saturated unless there is a very large number of users. For something this size though I would expect to find that they have a WAN accelerator or some kind of packet shaper that would usually be able to honour the QoS tags and prioritise them. The other option you may have is to partition part of the available bandwidth off only for RTP traffic. One assumes that the MPLS provider is honouring the QoS markings as it is passing through their network.

Do they have any kind of network management in place to see what traffic is being given higher/any priority over voice, and what would be consuming all of that bandwidth.

[LoopyLou]

Seems you have what you need. The sets will tag their packets with your L2 priority and DSCP values so as long as your network is set to prioritize those packets you should be good. The other thing you could consider is running compression on your IP trunks or use the bandwidth management built in the 3300 on your IP trunks.

[sfernandes]

Thanks for the responses guys.

I am aware that I have to do the QOS trust statements, but was hoping to dive a bit more technically into classifiers / policers if possible.


I.E based on my bandwidth measurements, I figure I need to reserve specifically 1.5 MEG for the MPLS for voice. Everything else can go on best effort session.

Oh and to answer the question of 100 Meg Saturation, we frequently transfer large data files between the two sites. That and all the media streaming that goes through, really chews through the pipe.

[sfernandes]

To get started:

On my 2960 access layer switches the config that I will have would be as follows:

interface giga x/0/x
switchport mode access
switchport access vlan X1
switchport voice vlan x2
spanning-tree portfaast
mls qos trust cos
mls qos trust dscp

---------------


Now I understand that mitel uses CDP and recognizes the phones, so I should have no problem by using voice vlan statement. Now that I have all my interfaces on my access layer switch say (1-48) with the above config, what will I need to do for the trunk ports that connect up to the my core layer 3 switch which does my Routing between the MPLS.

Currently on the 2960 Uplink it would be something like:

interface giga 1/0/52
switchport mode trunk
switchport trunk native vlan x3
switchport trunk allowed vlan nativeVlan voiceVlan dataVlan


-----

That would be my current config on the trunk ports. Would I have to add the following two lines:

mls qos trust cos
mls qos trust dscp

to the trunk interface?



I would like to iterate that same site calling is fine, but intersite calling is where I experience drops and jitter and hence I only need QOS really for the sites. But I am not sure if I have to enable these commands first on the access layer and then on the core layer switches. I imagine that I do not need to trust the qos on the access layer switches, as the frame should still have the priorities listed within it but just ignored by the switch.

Im rambling right now so ill stop here for now.

[sfernandes]

Any suggestions?

[LoopyLou]

Wish I could help but not really a network person. Not familiar with Cisco either so all the talk about trust is something beyond me. To me you have layer 2 priority on the edge switches and setup DSCP for any layer 3 routing that occurs. On the MPLS to our office we have a set amount of bandwidth into the office and in that bandwidth we have guaranteed or reserved bandwidth for voice. Sorry I can not be of more help.

[MrLouzada]

I have a similar setup - however my 100mbps is not on mpls.

On the port where 3300 is connected i have:

***************************************
interface GigabitEthernet0/45
 description MN3300 Controller
 switchport trunk encapsulation dot1q
 switchport voice vlan 30
 priority-queue out
 mls qos cos 5
 mls qos trust cos
 spanning-tree portfast
!
***************************************

Also on the same switch i create the dscp-qos map and enable qos

***************************************
mls qos map cos-dscp 0 8 16 26 32 46 48 56
mls qos
***************************************

Now for port (voice and data I do)

interface GigabitEthernet0/26
 switchport access vlan 10
 switchport trunk encapsulation dot1q
 switchport mode access
 switchport voice vlan 30
 priority-queue out
 mls qos trust cos
 spanning-tree portfast
!

****************************************
For the trunk ports add this statement on top of your trunk config:

 priority-queue out
 mls qos trust cos


The trunk port between the switches across locations is the same config as for switches between sites - however you must ensure Telus honour the dscp-qos settings you are sending across.
Now here is a little tip I can offer regarding Telus - Blame it on them - You should not have voice problems on a 100MPBS link unless you are always saturating it however being MPLS I would say you should not be experiencing any voice issues at all. In my opinion dealing with carriers they implemented they have to fix - they have cisco and mitel resources they can consult to ensure your QoS is working across sites - Even if i knew cause/fix i would dump the problem on them:

" Hey - you like to take my hard earned dollar every month for this connection - now that i have a problem you should do everything you can to fix it "

Good luck!

[sfernandes]

Louzada,

Thanks for the reply. I am currently working on getting this setup and will go from there. Will eventually post a config as well w/ specifics. I do have a question, did you do any class matching and policy set w/ policers?

Or did you strictly focus on the expedite queue

[martyn]

Just came across this article that covers LAN & WAN marking. It is for Cisco, but applies to Mitel as well.