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User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform
Chapter 1
QoS overview
1-1
Chapter 1 QoS Overview
1.1 About QoS
In traditional IP networks, all packets are processed equally. Each router processes the
packets with first-in first-out (FIFO) policy. It sends the packet to the destination in the
mode of best-effort, but the throughput, delay, delay jitter and packet discarding rate
cannot be predicted. The situation can be very perfect, or be very bad, and it can only
be determined by the state of the network. However, people raise higher demand for
the network along with the rapid development of computer network. As more and more
voice, image and important data are transmitted over the network, which are sensitive
to bandwidth, delay, jitter and real-time features, network resources now become
increasingly diversified. At the same time, the service quality also becomes an
important issue. People expect that they can get enough guarantee in the aspects of
the throughput, delay, delay jitter and discarding rate of packets, so that their special
requirements on the special services can be satisfied. People also expect that they
could obtain customized service quality according to the client types. One way to solve
this problem is to increase the bandwidth. But bandwidth increase is limited and costs a
lot. The problem can only be solved to a certain extent.
QoS (Quality of Service) indicates the integration of a series of technologies that permit
users to get predictable service quality in the aspects of throughput, delay jitter, delay,
and packet discarding rate. QoS (Quality of Service) provides network service function
with different service quality according to different demands. It can be said that the
capability of providing QoS is the basic requirement for future IP networks.
1.2 Three service types of QoS
Usually, the service of QoS is classified into the following three types:
I. Best-effort Service
Best-effort Service indicates to work with “the best effort”, but it cannot guarantee the
service quality.
II. Integra ted Service
This service type uses signaling mechanism to inform the data flow passing route to
obligate resource, so it can implement quality guarantee very well. Bur when the size of
the network is large, the cost is high, and then the integrated service is usually
applicable for the edge of network. The signaling used to transfer QoS request is RSVP
(Resource ReSerVation Protocol), which informs the QoS request of application to the
router.
The integrated service provides the following two types of services:
1) Guarantee: i.e., to provide guaranteed bandwidth and delay limit to satisfy the
application request
2) Load control: to guarantee that it would provides the packets services almost the
same as those when the network is not overloaded even if the network is