Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 974)

Quality of Service (QoS) Introduction
Software Reference for x310 Series Switches
38.2 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
Introduction
This chapter introduces the concept of Quality of Service (QoS) with particular reference to
Allied Telesis switches running the AlliedWare Plus
TM
Operating System.
The concept of QoS is a departure from the original networking concept of treating all
network traffic in the same way. Without QoS, all traffic types are equally likely to be
dropped when a link becomes oversubscribed. With QoS, certain traffic types can be given
preferential treatment. QoS is therefore a very useful tool both to control congestion and
to meter or cap data in order to apply pre-agreed service levels.
Operationally, QoS is applied within the link and network layers. Functionally it provides
the capability to intelligently transport your network traffic in order to provide stable and
predictable end-to-end network performance.
Business benefits Quality of Service mechanisms enable:
■ network service providers to sell different levels of service to customers, based on
what their customers require, and be confident in their ability to guarantee the
reliable delivery of these services
■ enterprise and educational organizations to actively manage and provide many
services across one network, for example live video streaming and standard data
services, with preferential treatment being given to mission-critical traffic
■ network administrators to manage network congestion as network traffic levels
increase and time-critical applications, such as streaming media, become more
widely in demand by customers and organizations
QoS Operations
Quality of Service is typically based on how the switch performs the following functions:
■ assigns priority to incoming frames (that do not already carry priority information)
■ correlates prioritized frames with traffic classes, or maps frames to traffic classes
based on other criteria
■ correlates traffic classes with egress queues, or maps prioritized frames to egress
queues
■ provides minimum and maximum bandwidths for traffic classes, egress queues, and/
or ports
■ schedules frames in egress queues for transmission (for example, empty queues in
strict priority or sample each queue)
■ re-labels the priority of outgoing frames
■ determines which frames to drop or re-queue if the network becomes congested
■ reserves memory for switching/routing or QoS operation (for example, reserving
buffers for egress queues or buffers to store packets with particular characteristics)