Draytek Vigor2800 Series User Manual page 66

There are two components within Primary configuration of QoS deployment:
Classification: Identifying low-latency or crucial applications and marking them for
high-priority service level enforcement throughout the network.
Scheduling: Based on classification of service level to assign packets to queues and
associated service types
The basic QoS implementation in Vigor routers is to classify and schedule packets based on
the service type information in the IP header. For instance, to ensure the connection with the
headquarter, a teleworker may enforce an index of QoS Control to reserve bandwidth for
HTTPS connection while using lots of application at the same time.
One more larger-scale implementation of QoS network is to apply DSCP (Differentiated
Service Code Point) and IP Precedence disciplines at Layer 3. Compared with legacy IP
Precedence that uses Type of Service (ToS) field in the IP header to define 8 service classes,
DSCP is a successor creating 64 classes possible with backward IP Precedence compatibility.
In a QoS-enabled network, or Differentiated Service (DiffServ or DS) framework, a DS
domain owner should sign a Service License Agreement (SLA) with other DS domain owners
to define the service level provided toward traffic from different domains. Then each DS node
in these domains will perform the priority treatment. This is called per-hop-behavior (PHB).
The definition of PHB includes Expedited Forwarding (EF), Assured Forwarding (AF), and
Best Effort (BE). AF defines the four classes of delivery (or forwarding) classes and three
levels of drop precedence in each class.
Vigor routers as edge routers of DS domain shall check the marked DSCP value in the IP
header of bypassing traffic, thus to allocate certain amount of resource execute appropriate
policing, classification or scheduling. The core routers in the backbone will do the same
checking before executing treatments in order to ensure service-level consistency throughout
the whole QoS-enabled network.
However, each node may take different attitude toward packets with high priority marking
since it may bind with the business deal of SLA among different DS domain owners. It's not
easy to achieve deterministic and consistent high-priority QoS traffic throughout the whole
network with merely Vigor router's effort.
For more effective QoS deployment, you should check the available ADSL upstream and
downstream speed in Online Status as indicated below before you configure the QoS setting.
The following QoS policies will be defined in the form of ratio of upstream/downstream speed.
We will also provide application QoS requirement as reference to help you accomplish this
task. The setting values will vary depending on the network condition.
Click on Application >>QoS Control. The following screen will appear.
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Vigor2800 Series User's Guide