SmartSwitch Router User Reference Manual 291Chapter 21QoS ConfigurationGuideQoS & Layer-2/Layer-3/Layer-4 Flow OverviewThe SSR allows network managers to identify traffic and set Quality of Service (QoS)policies without compromising wire speed performance. The SSR can guaranteebandwidth on an application by application basis, thus accommodating high-prioritytraffic even during peak periods of usage. QoS policies can be broad enough to encompassall the applications in the network, or relate specifically to a single host-to-host applicationflow.The SSR provides four different features to satisfy QoS requirements:• Traffic prioritization allows network administrators to identify and segregate mission-critical network traffic into different priority queues from non-critical network traffic.Once a packet has been identified, it can be assigned into any one of four priorityqueues in order to ensure delivery. Priority can be allocated based on any combinationof Layer-2, Layer-3, or Layer-4 traffic.• Weighted Random Early Detection (WRED) alleviates traffic congestion by randomlydropping packets before the queue becomes completely flooded. WRED should onlybe applied to TCP traffic.• Type of Service (ToS) rewrite provides network administrators access to the ToS octet inan IP packet. The ToS octet is designed to provide feedback to the upper layerapplication. The administrator can “mark” packets using the ToS rewrite feature sothat the application (a routing protocol, for example) can handle the packet based on apredefined mechanism.• Traffic rate limiting provides network administrators with tools to manage bandwidthresources. The administrator can create an upper limit for a traffic profile, which isbased on Layer-3 or Layer-4 information. Traffic that exceeds the upper limit of theprofile can either be dropped or re prioritized into another priority queue.
