H3C Technologies H3C SR8800 - Manual (Page 28)

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QoS overview
NOTE:
In this documentation, SPC cards refer to the cards prefixed with SPC, for example, SPC-GT48L, and SPE
cards refer to the cards prefixed with SPE, for example, SPE-1020-E-II.
Introduction to QoS
In data communications, Quality of Service (QoS) is the ability of a network to provide differentiated
service guarantees for diversified traffic in terms of bandwidth, delay, jitter, and drop rate.
Network resources are always scarce. The contention for resources requires QoS to prioritize important
traffic flows over trivial ones. When making a QoS scheme, a network administrator must consider the
characteristics of various applications to balance the interests of diversified users and fully utilize network
resources.
Networks without QoS guarantee
On traditional IP networks without QoS guarantee, routers treat all packets equally and handle them
using the first in first out (FIFO) policy. All packets share the resources of the network and routers. How
many resources the packets can obtain completely depends on the time they arrive. This service is called
best-effort. It delivers packets to their destinations when it can, without any guarantee for delay, jitter,
packet loss ratio, and so on.
This service policy is only suitable for applications insensitive to bandwidth and delay, such as Word
Wide Web (WWW) and email.
QoS requirements of new applications
The Internet is growing along with the fast development of networking technologies.
Besides traditional applications, such as WWW, email, and FTP, network users are experiencing new
services, such as tele-education, telemedicine, video telephone, videoconference, and
Video-on-Demand (VoD). Enterprise users expect to connect their regional branches together with VPN
technologies to carry out operational applications, for instance, to access the database of the company
or to monitor remote routers through Telnet.
These new applications all have special requirements for bandwidth, delay, and jitter. For example,
videoconference and VoD require high bandwidth, low delay and jitter. As for mission-critical
applications, such as transactions and Telnet, they may not require high bandwidth, but do require low
delay and preferential service during congestion.
The emerging applications demand higher service performance of IP networks. Better network services
during packets forwarding are required, such as providing dedicated bandwidth, reducing packet loss
ratio, managing and avoiding congestion, and regulating network traffic. To meet these requirements,
networks must provide more improved services.