VI. Feature Setup

Vigor QOS: Enforcing Internet traffic priority

Vigor 2820
Bandwidth Management
Quality of Service

The Vigor router will normally distribute the available Internet bandwidth equally between all local users and all applications. Thus if you have 1Mb/s of download capacity and Jacob downloads a file from a web site and Esau downloads a large email at the same time, each of them would be allocated 50% of that capacity, i.e. 512Kb/s (For simplicity, in this example we are ignoring contention, congestion and protocol overheads).

In the case of a file download, although it's "nice" to have the file quickly, it's quite acceptable to merely receive the file as soon as resources allow, taking into account the demands and needs of other, equally important users and applications, and whilst the download proceeds, you can get on with other work.

In the earlier example, we assumed that Jacob's File download was no more or less important than Esau's email, but actually it might be. To elaborate on the example, Jacob's file download is a software patch for a computer game - low priority for his company, and Jacob is quite happy to wait all day, after which he will burn the file onto a CD-Rom and take it home, which is where he needs it; he really doesn't care if it takes 10 minutes or 3 hours - it's very low priority for the company. Esau, on the other hand, needs that email - it's a vital spreadsheet file from the New York office, which he needs to review by 10AM - Esau's email is very high priority for the company. This is what QoS is all about - giving different priorities to different types of data or users and allocating them Internet bandwidth appropriately.

DrayTek's Quality of Service Assurance (QoS) allows you to select sets of traffic types and give each type a guaranteed percentage of the available bandwidth. Using the earlier example again let's imagine that http downloads have been given a very low priority of 10%, and email downloads a high priority of 90%. If Jacob is the only person using the Internet, his http file download will come in at 1Mb/s, but as soon as Esau starts his email download, Jacob's download speed will drop to 0.1Mb/s, whilst Esau gets 0.9Mb/s - 90% of the bandwidth.

Other applications require not only that the data arrives as soon as possible, but the immediacy is vital, otherwise the application is unusual. The best example of this is VoIP (Voice over IP) - carrying person to person voice calls across your Internet connection. Whilst you can wait for a file download, you cannot wait for VoIP packets as they have to be received at re-assembled at a constant rate in order for the voice to to be intelligible. For VoIP, therefore, QoS becomes a very important and useful feature.

Whilst priority for applications will depend on your own specific requirements, VoIP is assumed to always be the highest priority traffic. As such, if your Vigor router supports QoS, SIP VoIP traffic is always allocated as much bandwidth as it needs; VoIP protocols generally use between 8-32Kb/s of bandwidth, so whilst it will be prioritised and sent immediately, you will normally still have plenty of other bandwidth available on a typical broadband line.

For those interested how the actual bandwidth is used by the QoS system, it works by queuing packets. If we have a 90%:10% split, then assuming that all IP packets are the same size, the router will forward 9 data packets for Esau, 1 data packet for Jacob, then another 9 for Esau and so on. This is illustrated below :

QoS on Vigor Routers

The Vigor's QoS facility allows you to differentiate traffic types on the following criteria :

  • TCP/UDP Port Numbers
  • Internal Client IP Address (e.g. a server on
  • Remote IP Address/Subnet (e.g. a mail server, or remote office)
  • Direction - Inbound or Outbound

As an example, imagine we are running an internal Web server for remote users to access information. We want remote users to have reliable access our web servers, so our criteria could be to ensure that min. 50% of available bandwidth is made available for outbound http transmission (http is the protocol used for web serving, normally on TCP Port 80). We can therefore set a simple QoS rule to guarantee outbound HTTP traffic 50% of available bandwidth. The setup of this within the Vigor's user interface will look something like this :

QOS Simple

Remember that the 50% set for http traffic does not permanently set that bandwidth aside. If http downloads are not using it, then the bandwidth is fully available for other applications.

You can set more complex rules and several sets of QoS priorities - for example give different departments higher priorities than others - for further details, refer to the full manual supplied with your router (on the CD-Rom). Of course, with QoS in operation the router has to classify every data packet, providing an increased CPU overhead; therefore, for maximum router performance, disable QoS when not required.

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