VI. Feature Setup

Quality of Service Configuration & Setup Examples

Products:
Vigor 2620Ln
Vigor 2760
Vigor 2762
Vigor 2765
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Keywords:
Bandwidth
DSCP
DiffServ
Jitter
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The Quality of Service system available on DrayTek routers allows for full control of how traffic is prioritised and bandwidth is reserved, with five queues available.

The router assigns sessions to each one of these queues and schedules packets to be sent through the router in order of priority instead of "first come, first served", with reserved bandwidth available to each queue, to ensure that important data can always be sent.

Prioritisation

The Class 1, Class 2 and Class 3 classes are configurable and used to prioritise traffic over each lower priority class, with the lowest class being unclassified traffic, referred to as the Others class.

This is useful to avoid delays for traffic that depends on low latency such as prioritising VoIP over Email traffic. Packets in the higher priority queues are sent as quickly as possible by delaying packets in the lower priority queues.

Bandwidth Reservation

The priority Classes 1, 2 and 3 can have a reservation for bandwidth if the available bandwidth amount needs to be guaranteed. If for example there are multiple VoIP calls in progress, they may require a certain amount of bandwidth reserved while calls are in progress, so normal internet traffic could be throttled back slightly. This is done by setting the percentage to reserve for the class and is only active while that traffic is detected in that class.

QoS Example

 

Configuring Quality of Service

Configuring Quality of Service to match your requirements is recommended to get the best results from it.

It's not ideal to use a default configuration for Quality of Service settings; bandwidth reservations and priorities will differ significantly between different Internet connections (throughput) and with different network requirements.

Connection Speeds


Quality of Service requires the router to be aware of the Bandwidth available (speeds that can be achieved) on each Internet connection to be able to prioritise correctly. This allows the router to properly schedule packets, so that they can be transmitted through the Internet connection at the correct speed and bandwidth is shared correctly between different Priority queues.

ADSL / VDSL Internet Connections

DrayTek Vigor routers that have an integrated ADSL or VDSL modem will automatically determine the Quality of Service Bandwidth values. DrayTek Vigor routers that connect to ADSL or VDSL with a modem connected to the router's Ethernet WAN port will need the Bandwidth to be set manually.

Ethernet-based Internet Connections

When using an Ethernet WAN interface, the router will need to have the Bandwidth for the WAN configured manually. This method is necessary when using an ADSL or VDSL modem with the router's Ethernet WAN port.

There are two ways to determine this:

  1. Bypass the DrayTek router, by connecting a PC directly to the Internet connection and perform a Speed Test using any popular speed testing site or App:

    Speed Test Result

  2. Disable Quality of Service on the router and perform the speed test using that Internet connection - this is the less reliable method as other devices could be using the Internet connection

Once the available Bandwidth on the Internet connection has been determined, go to [Bandwidth Management] > [Quality of Service] and click Setup for the Internet connection being configured.

Set the Bandwidth values to be 90-95% of the maximum achievable on that Internet connection to get the best results from Quality of Service.

Note: If the bandwidth boxes are greyed out then they don't need to be set. DrayTek Vigor routers with an integrated ADSL or VDSL modem will automatically determine the line speed.

WAN 2 QOS Speed

Following the above "speed test" example, the Bandwidh of this Internet connection is set to around 90% of that throughput.

Values are specified in Kilobits or Megabits per second; be careful to avoid using Kilobyte or Megabyte values when specifying QoS Bandwidth values. A Kilobyte is 8 times larger than a Kilobit.


Configuring Priority Classes


From [Bandwidth Management] > [Quality of Service], click Setup for the Internet connection to configure QoS for each interface that QoS will be applied to.

Enable the QoS Control

Tick this option to enable QoS on this interface.

Set the direction that QoS will affect, the default is "OUT", which affects outbound / upload only. Setting this to "BOTH" will affect both directions, upload and download traffic.

Reserved Bandwidth Ratio

Each Class can be left on its default setting of 25% and give good results with QoS. When changing the values, the four classes must add up to 100% total.
This operates by reducing the bandwidth available by the percentage specified to the lower priority queues when traffic is detected in the higher priority queue. When there are no packets / sessions in the higher priority queue, that bandwidth is available to the other queues.
It is recommended to calculate the required bandwidth for the application and reserve only the amounts required. Setting a high reservation value for one Class queue can disrupt traffic in lower priority queues.

A good example of bandwidth reservation would be a Voice over IP system where there are 10 phones that could all make calls at the same time. They will each use a VoIP codec that can use up to 100Kbps in each direction, therefore they would ideally have a reservation of 1000Kbps (1 Megabit) in each direction. If the Internet connection has 4000Kbps in each direction, this would be a 25% reservation.

Higher priority classes can use the bandwidth percentages available to lower priority classes when required.

Traffic types that use a small amount of data but require low latency can use a smaller reserved bandwith percentage to minimise impact on other queues.

Enable UDP Bandwidth Control Used to throttle the amount of bandwidth available for UDP traffic, it is recommended to leave this disabled when using VoIP as this could significantly limit available bandwidth to UDP based VoIP traffic.
Outbound TCP ACK Prioritise Used to prioritise TCP packet acknowledgements, it can be beneficial when there isn't enough upload bandwidth for TCP ACK packets to respond quickly, which could result in lower download speeds, as TCP sessions would not be able to respond in time so that the next packet can be sent.

QoS Page WAN 1

Click OK to apply the changes for the Quality of Service configuration for that interface.

It is recommended to test each setting to check whether it benefits or impacts network performance depending on the configuration.


Classes

These are used to group the services or IP addresses to prioritise, with Class 1 being the highest priority queue and Others (traffic not otherwise classified) being the lowest priority.

Each class needs to have rules assigned to it to classify traffic.

To configure a QoS Class, go to [Bandwidth Management] > [Quality of Service] click the Edit for Class 1, 2 or 3. This will display a list of Rules for each Class.

Click Add to create a new QoS Rule for that Class:

RTP Class Rule

ACT Enables the QoS Rule
Ethernet Type Set this to define whether it is classifying IPv4 or IPv6 traffic
Local Address Used to define the local IP address as a single IP, range IP or subnet IP
Remote Address Used to define the internet / VPN address as a single IP, range IP or subnet IP
DiffServ CodePoint

If the IP traffic has a DSCP packet tag applied to it, this can be used to classify that traffic.

It can often be configured on switches / phones for different traffic types

Service Type Used to specify which TCP / UDP / protocol that would be classified

Service Types

These are used to specify the traffic types for the QoS Class Rules, there are some predefined Service Types that can be selected when making a new QoS Class Rule such as HTTP or FTP.

There are some Service Types that cannot be easily defined, for instance RTP (Real Time Protocol) used for VoIP audio packets could potentially use any UDP port between 1 and 65535, which would limit the effectiveness of QoS. In this situation, it's best to determine which ports are used specifically by the service on your network and create Service Types for that specific range.

To create a new Service Type, go to [Bandwidth Management] > [Quality of Service] and in the [Service Type] section, click Edit and enter the details for the service: