Prioritizing VOIP traffic in your Network

When there are no QOS polices applied on a network, there is equal priority for all traffic passing through the network. This is when congestion occur. Configuring QOS helps select a specific traffic to be prioritized, which makes this traffic to be delivered on time and thus improving the performance.

In this blog we can see how we can mark the VOIP traffic with a DSCP value and send this traffic through the network with priority. We have taken two ways of Prioritizing.

1) Prioritizing using ACL:

Create your access list according to your network, based on the VOIP traffic. For eg: If the VOIP traffic will be from a particular Ip address or IP range. Create an Access group with the concerned IP address or the IP range. Consider we have given an Access group name Voip-group.

Now we can create a class-map with the name Voip-Traffic and add the ACL,

class-map Voip-Traffic
match access-group Voip-group
set ip dscp ef

Next step will be to create a policy-map, here we have shown steps to create a policy-map with name voip_policy. Configure the class-map to “trust” DSCP values and giving priority for the voice traffic.

policy-map voip_policy
class Voip-Traffic
priority  xxxx    // where xxxx is the priority to be given for the concerned policy in Kilo Bits per sec<8-2000000>
trust dscp

Now we have taken care of the priority, we have to apply this Policy Map to an interface. Most of the cases the Policy Map will be applied to the outside of the WAN interface.

router(config-if)#service-policy output voip_policy

2) Prioritizing using class maps and policy maps:

Here we do not have to create a ACL, however, we have to match the traffic based on a criteria. Here we have taken a criteria UDP traffic using a specific port.

class-map match-any Voip-Traffic
match port udp eq yyyy     //where yyyy is the port your voip traffic is using

To create a policy-map, configure the class-map to “trust” DSCP values, setting the traffic with DSCP value EF and giving priority for the voice traffic.

policy-map voip_policy
class Voip-Traffic
set ip dscp ef
priority  xxxx    // where xxxx is the priority to be given for the concerned policy in Kilo Bits per sec<8-2000000>

As mentioned earlier we have to apply the Policy Map to an interface.

service-policy output voip_policy

Hope this configuration helps in prioritizing VOIP traffic. This configuration can also be used to prioritize the business critical application that none of these traffic gets dropped in the Network.

Once you have configured QoS in your network, you can use NetFlow Analyzer to monitor the QoS in the Network.

You can download the 30 day trial from here.

Praveen Manohar
NetFlow Analyzer Technical Team


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