Quality of Service (QoS)

What is QoS?

Quality of Service (QoS) refers to the prioritization of traffic throughout a network. In the context of your Intulse services, this term refers to giving priority to voice and video transmissions over other traffic types like general internet browsing or file transfers. Particularly in scenarios where bandwidth is limited, properly configured QoS is crucial if maximum call quality is to be obtained. Properly implemented, QoS can reduce congestion, latency, and packet loss—all of which negatively impact call quality.

Configure QoS

There are several different ways to implement QoS, and network admins should use the option that best fits their network environment. The strategies discussed below pertain to traffic inside a Local Area Network (LAN) and between the hand-off from a LAN to a Wide Area Network (WAN). Any QoS set up on a WAN connection itself must be configured by your internet service provider (ISP).

Physical Network Separation

A popular way to ensure network quality is to physically separate voice and data networks. This method involves using a dedicated WAN connection for voice only, and using separate WAN connections for data traffic.

Balancing or Policy-Based Routing

Another method for achieving QoS on a LAN is logical network separation. Networks can be separated into logical divisions or Virtual Area Networks (VLANs) to separate voice from lower priority traffic. This traffic balancing, or policy-based routing, can allocate bandwidth dynamically based on volume, or statically by manual assignment.

If you have multiple WAN connections you can configure your network to route your voice VLAN out one WAN connection and all other VLANs over another. In this scenario, saturation of the "data" WAN connection is irrelevant, as all voice traffic is routed over its own WAN connection.

Class of Service / DSCP

Routers and gateways can be configured to honor Layer 3 DSCP values. Layer 2 802.1p/CoS values can also be used, though DSCP is preferred.

Test QoS

On higher-end LAN equipment, proper QoS policies can be verified by watching the traffic flows and/or queues. If this is not possible, a handful of empirical tests can also be used:

  1. Saturate the LAN connection by transferring large files between computers on the LAN. Then make several concurrent phone calls.
  2. Saturate the upstream portion of the WAN connection by uploading several large files. Then make several concurrent phone calls.


Do I really need to implement QoS?

It is usually recommended, but whether or not it is needed depends on the nature of your network and how likely you are to saturate bandwidth on any one of your links.

For example:

  • A switched network environment typically means that QoS implementation on the LAN would be needed for large campus environments, but would be less likely needed for smaller offices.
  • Implement QoS on the egress WAN connection (hand-off) if upload bandwidth has the likelihood of being saturated. If not, avoid QoS as it could cause other traffic that is not voice to bottleneck.

What's the best way to implement QoS?

The best way to implement QoS is to implement as many of the following as possible:

  1. Physically separate phones and other connections (data) with dedicated wiring.
  2. Logically separate phones and other connections (data) through the use of voice VLANs.
  3. Use CoS (layer 2) and DSCP (layer 3) values.

What ports should I use to enable QoS on my router?

Port prioritization is not recommended because it will be a random port between 20,000 – 60,000. If this is your only method to implement QoS, it is best to purchase a new router.