Riverstone Networks WICT1-12 - Manual (Page 563)

Riverstone Networks RS Switch Router User Guide Release 8.0 26-1
26 QOS CONFIGURATION
The RS allows network managers to identify traffic and set Quality of Service (QoS) policies without
compromising wire speed performance. The RS can guarantee bandwidth on an application by application basis,
thus accommodating high-priority traffic even during peak periods of usage. QoS policies can be broad enough to
encompass all the applications in the network, or relate specifically to a single host-to-host application flow.
The RS provides four different features to satisfy QoS requirements:
Traffic Prioritization – Allows network administrators to differentiate between mission-critical network traffic
and non-critical network traffic and segregate the traffic into different priority queues . Once a packet has been
identified, it can be assigned to any one of the four priority queues in order to ensure delivery. Priority can be
allocated based on any combination of Layer-2, Layer-3, or Layer-4 traffic.
Weighted Random Early Detection (WRED) – Alleviates traffic congestion by randomly dropping packets
before the queues pass their upper thresholds. WRED is intended to work with connection-oriented protocols
(especially TCP). However, WRED when applied to a port receiving connectionless traffic can reduce latency on
that port.
Type of Service (ToS) – ToS Rewrite provides network administrators access to the ToS octet in an IP packet. The
ToS octet is designed to provide feedback to the upper layer application. The administrator can mark packets using
the ToS rewrite feature so that the application (a routing protocol, for example) can handle the packet based on a
predefined mechanism.
Traffic Rate Limiting – Provides network administrators with tools to manage bandwidth resources. The
administrator can create an upper limit for a traffic profile, which is based on Layer-3 or Layer-4 information.
Traffic that exceeds the upper limit of the profile can either be dropped or re-prioritized into another priority
queue.
Within the RS, QoS policies are used to classify Layer-2, Layer-3, and Layer-4 traffic into the following priority
queues (in order from highest priority to lowest):
• Control
• High
• Medium
• Low
Note Control is for router control traffic. The remaining classes are for normal data
flows.