What is QoS?

Quality of Service, or QoS, is a type of traffic shaping technology that enables you to determine the importance of different traffic on your network. In this context, we are primarily thinking about configuring QoS on the router for your local area network (LAN).

Traffic shaping, or packet shaping, is a type of network traffic management that delays some packets whilst allowing others to travel freely. It is used to shape traffic to conform with a predefined traffic profile.
A local area network, or LAN, is a computer network that connects devices within a limited area, such as your office. The computers on this network have local addresses and are not directly connected to the public Internet.

There are many different types of traffic being routed across our networks each day. These different types of traffic are known as network protocols . Some protocols are used to help computers find each other and know where to send traffic. Others are the protocols on top of which the services we use are built.

A network protocol defines rules for communication between one or more devices. Most protocols use packet switching techniques to send and receive messages known as packets.

For example, the email service is built of top of a number of network protocols, such as POP, IMAP, SMTP and many others. Another example is the web sites that we visit, which are built on top of another protocol that you have probably heard of called HTTP. In the same way, VoIP calls also depend on a number of types of network protocol - SIP and RTP being the most well known examples.

When traffic is low, you won't experience any problems at all, but what happens when there's a bottleneck?

Well once the amount of available bandwidth is in short supply, then just like with a road system that is congested, the network traffic begins to queue. Some technologies cope with this queueing better than others. If the web page you are loading takes a second or two longer to load than normal, you probably won't even register the difference. However a VoIP call, particularly the audio part of the call, is very sensitive to this type of bottleneck. If packets take too long to route then you will notice this as poor audio quality and this is when configuring QoS can make a huge difference to your network.

Configuring your QoS router

Configuring QoS is mostly about limiting the bandwidth available to different devices and protocols. It's not particularly difficult to configure QoS once you understand a few basic principles. We'll walk you through these below.

Whitelist VoIP devices

Most routers will let you specify devices by IP address or IP subnet that you either want to limit or provide unrestricted access to. If you know that your provider has a fixed range of IP addresses, then you can whitelist those devices and be sure that traffic to and from those addresses is never limited.

An Internet Protocol address, or IP address, is a numeric label assigned to each device in an IP network. For example and are both IP addresses.
An IP subnet is a notation for expressing a range of IP address. For example, the subnet notation refers to the IP addresses in the range of

In the same way, if you are using hardware phones, you could put all of your phones onto their own subnet and ensure that they get unrestricted access to the available bandwidth. If subnetting is not an option, then you could maintain a list of IPs for your phones that are whitelisted in the same way.

Blacklist regular offenders

Set up some kind of monitoring and keep an eye on the users on your network. Some staff can be much bigger users of bandwidth than others. If a particular user is often downloading large files or watching a lot of video, then set them a bandwidth limit by IP address or MAC address and ensure that they cannot create a bottleneck that then impacts your voice calls.

A media access control address, or MAC address, is a unique identifier assigned to each network interface on a network. MAC addresses are usually assigned by the manufacturer when the device is made and are stored in the hardware itself. Hardware MAC addresses are, in thoery at least, globally unique.

Whitelist VoIP protocols

It's always a good idea to whitelist or prioritise the VoIP protocols being used on your network. The standard VoIP protocols are SIP over UDP for signalling and RTP over UDP for audio/media, but there are many more out there including SIP over TCP or TLS, SRTP, ZRTP and many more.

The User Datagram Protocol, or UDP, is part of the Internet Protocol collection of protocols. UDP is a connectionless protocol, sometimes thought of as fire and forget. It is both fast and lightweight, but can also be unreliable due to its lack of error handling.

Once you have determined the protocols in use for your VoIP service, then you can set about whitelisting them. For example, with standard SIP over UDP it's a good idea to whitelist UDP ports 5060-5080. With RTP over UDP you probably need to open up a large range of UDP ports - such as 10,000-20,000 or 50,000-60,000 - but you will need to talk to your SIP provider to confirm the range that they use.

Blacklist less important protocols

As we mentioned briefly above, some types of traffic are relatively resilient to small delays. A good example of this is HTTP, where an HTTP page or other resource taking 500ms longer to load is barely noticeable. Other services you might want to limit might be things like video streaming (YouTube!), FTP and even the protocols used for file sharing applications like BitTorrent.

There have been many times we've been asked to investigate some call quality issues on a customer's network and upon investigation we've discovered a user on the network who is doing things on their PC that have not been approved by their manager!

The File Transfer Protocol, or FTP, is a protocol used to transfer files from one device to another over a TCP connection.

Select a quality VoIP provider

Configuring QoS for your network can really make a difference, but obviously you need to be using a quality SIP provider in the first place. If you're not getting the kind of call quality that you want from your current provider, then please take a look at the products that we have available.

SIP trunks

For those who already have on-site soft or hardware PBX equipment, you'll benefit from the fantastic performance and highly competitive call rates found in our SIP trunking solution.

Cloud PBX

For companies who want to out-source the running costs and management of their phone systems to the cloud, then our Cloud PBX will provide you with a state-of-the-art hosted PBX solution without any of the technical headaches that come with managing your own telephony infrastructure.

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