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How do I configure QoS settings?

Use as many of the following methods as you can to implement QoS if your upload bandwidth is likely to be saturated.

Before you begin: If it is unlikely that your bandwidth will be saturated, we recommend that you avoid QoS as it could bottleneck other non-voice traffic.

Context: The strategies discussed below pertain to traffic inside a Local Area Network (LAN), 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). It is not possible to prioritize a phone that is making a call over a phone that is downloading its configuration or firmware files at the same time.

Ways to implement QoS

Physical Network Separation

  • A popular way to ensure strong network quality is to physically separate voice and data networks via separate routers/firewalls, switches, and ports for your phones. Essentially, you would use a dedicated WAN connection for voice only and 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. If DSCP values are not available, then utilizing our IP blocks as the source (ingress) or destination (egress) for all our traffic is a valid option as well.
  • When configured by us, VoIP devices set a DSCP value in the header of each packet they generate as shown here:
Traffic Type Traffic Purpose DSCP Value 802.1p/CoS Value
SIP Call Control 26 5
RTP Call Media (the media conversation) 46* 5
  • To enable QoS within a LAN and over a LAN-to-WAN hand-off, the network should be configured to prioritize traffic carrying those tags over all other traffic.
  • Implementing Downstream QoS (ingress) on your internet connection requires the cooperation of your ISP, as there is very little that can be done on a LAN to prevent saturation of the downstream link.

Port Prioritization — Not recommended

  • We do not recommend port prioritization because traffic will be over a random port between 20,000 and 60,000. If this is your only method to implement QoS, it is best to purchase a new router.

Ways to 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:

  • Saturate the LAN connection by transferring large files between computers on the LAN, then make several concurrent phone calls.
  • Saturate the upstream portion of the WAN connection by uploading several large files, then make several concurrent phone calls.
Article last updated: 22 April, 2022