Cisco SR224T Administration Guide - Page 271

Configuring Quality of Service QoS Features and Components 20 QoS Features and Components The QoS feature is used to optimize network performance. QoS provides the following: • Classification of incoming traffic to traffic classes, based on attributes, including: - Device Configuration - Ingress interface - Packet content - Combination of these attributes QoS includes the following: • Traffic Classification-Classifies each incoming packet as belonging to a specific traffic flow, based on the packet contents and/or the port. The classification is done by ACL (Access Control List), and only traffic that meets the ACL criteria is subject to CoS or QoS classification • Assignment to Hardware Queues-Assigns incoming packets to forwarding queues. Packets are sent to a particular queue for handling as a function of the traffic class to which they belong. • Other Traffic Class-Handling Attribute-Applies QoS mechanisms to various classes, including bandwidth management. QoS Operation When using the QoS feature, all traffic of the same class receives the same treatment, which consists of a single QoS action of determining the egress queue on the egress port, based on the indicated QoS value in the incoming frame. This is the VLAN Priority Tag (VPT) 802.1p value in Layer 2 and the Differentiated Service Code Point (DSCP) value for IPv4 or Traffic Class (TC) value for IPv6 in Layer 3. When operating in Basic Mode, the switch trusts this external assigned QoS value. The external assigned QoS value of a packet determines its traffic class and QoS. The type of header field to be trusted is entered in the Global Settings page. For every value of that field, an egress queue is assigned, indicating through which queue the frame is sent, in the CoS/802.1p to Queue page or the DSCP to Queue page (depending on whether the trust mode is CoS/802.1p or DSCP, respectively). Cisco Small Business 200 Series Smart Switch Administration Guide 272