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Re: QOS Implementation for VOIP

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Occasional Contributor

QOS Implementation for VOIP

I am new to QOS and want to configure switches properly for my implementation. I am installing a Shoretel phone system and am planning on segmenting a Voice VLAN with the "voice" option enabled. I'm not sure if it's priority 6 or 7, as the setting or if it even matters. I understand 802.1p is Layer 2 only and in order to maintain QOS settings over layer 3, there has to be some sort of DSCP map that takes place. I've read the advanced traffic guide and I'm having a hard time determining what needs to be done. I've added a basic diagram that resembles my network. Core switch is 8600 and clients are 2910s. Thanks for all the help.

Frequent Advisor

Re: QOS Implementation for VOIP

Hello Jstew,


I haven't checked the QoS features on the 2910's, but assuming they are similar to the 8200 you have you would want to do the following:


  1. Enable your switchesto inspect DiffServ traffic with the qos type-of-service diff-services command.
  2. Configure your DSCP to DOT1P mappings. (For example qos dscp-map 100110 priority 6 ).  This makes sure that certain DSCP values get treated appropriately and sends traffic out the correct queues.
  3. Depending on the granularity you'll want to set your output queues.  I use all 8, but for your network 4 would probably suffice.  You can change this with the qos queue-config x command. Default is 8 and if you change this you will need to reboot your switches.                                                                                                                                                                                                                       

Technically you would not need to do anymore since your voice traffic from the shoretel should be marked as EF by the shoretel configuration.  You can however classify and mark call signaling traffic and other types of traffic if you wanted to get more granular as to what types of traffic get what type of treatment.  Here's a good link on Shoretel QOS requirements.

  Shoretel QoS


If you're going to want to classify, mark and treat traffic at that level you'll want to make sure your DSCP to DOT1P values are set accordingly and that you have QoS policies to perform the classification and marking.  Here's an example of that.


     10 match tcp eq 2598
     20 match tcp eq 1494
class ipv4 "CALL-SIGNALING"
     10 match tcp eq 5440
     20 match tcp eq 111
     30 match tcp eq 31453
     40 match udp eq 31453
     50 match udp eq 111
     60 match udp eq 2427
     70 match udp eq 2727
     80 match udp range 5440
policy qos QOS
 class ipv4 "INTERACTIVE-VIDEO" action dscp af41
 class ipv4 "CALL-SIGNALING" action dscp af31


interface xxx
service-policy QOS in

So the above example will create traffic classifiers to look for traffic on the ports identified, mark them with DSCP values included in the QOS policy and send out the appropriate priority queues for any port on which this policy is enabled. 


With that you may not even need too much QOS as long as bandwidth is sufficeint.  Hopefully this helps a bit. 

Occasional Contributor

Re: QOS Implementation for VOIP



Thanks so much for the insight.  It is becoming much clearer now.  I do have a follow up question.  In regards to the DSCP settings and the map, does this get configured on every switch in the network or just the devices that are connecting the WAN Links?  I appreciate your very detailed and accurate post.  It really helps bring the concep together.



Frequent Advisor

Re: QOS Implementation for VOIP

Not a problem, glad it helped!  


In regards to your question, its usually best to configure QoS throughout the network, so that behavior is consistent.  At minimum, if you have traffic traversing the other switches that you want treated a certain way, then you should configure your mappings, markings, and service policies on those switches too.


I left one thing out of my original post.  You have the option of configuring GMB on your switchport egress queues as well.  This, you may just want to configure on your uplinks or WAN links where the potential for congestion is higher. 




Occasional Contributor

Re: QOS Implementation for VOIP

Shoretel QoS   <<<<<  broken LINK