Filter
Top Products
DES-7200 Configuration Guide Chapter 2 QoS Configuration
2-1
2 QoS Configuration
2.1 QoS Overview
The fast development of the Internet results in more and more demands for multimedia
streams. Generally, people have different service quality requirements for different
multimedia, which requires the network to be able to allocate and dispatch resources
according to the user demands. As a result, the traditional "best effort" forwarding
mechanism cannot meet the user demands. So the QoS emerges.
The QoS (Quality of Service) is used to evaluate the ability for the service provider to
meet the customer demands. In the Internet, the QoS mechanism is introduced to
improve the network service quality, where the QoS is used to evaluate the ability of
the network to deliver packets. The commonly-mentioned QoS is an evaluation on the
service ability for the delay, jitter, packet loss and more core demands.
2.1.1 Basic Framework of QoS
The devices that have no QoS function cannot provide the capability of transmission
quality service, and will not ensure special forwarding priority for certain dataflow.
When bandwidth is abundant, all the traffic can be well processed. But when
congestion occurs, all traffic could be discarded. This kind of forwarding policy is
otherwise called the service of best effect, since the device now is exerting its
performance of data forwarding and the use of its switching bandwidth is maximized.
The device of this module features the QoS function to provide transmission quality
service. This makes it possible to select specific network traffic, prioritize it according
to its relative importance, and use congestion-management and congestion-avoidance
techniques to provide preferential treatment. The network environment with QoS
configured is added with predictability of network performance and allocates network
bandwidth more effectively to maximize the use of network resources.
The QoS of this device is based on the DiffServ (Differentiated Serve Mode) of the
IETF Internet Engineering Task Force. According to the definitions in the DiffServ
architecture, every transmission message is classified into a category in the network,
and the classification information is included in the IP packet header. The first 6 bits in
the ToS (Type of Service) field for IPv4 packet header or the Traffic Class field for Ipv6
packet header carry the classification information of the message. The classification
information can also be carried in the Link layer packet header. Below shows the
special bits in the packet: