Dell PowerConnect 6248 User's Guide - Page 701

Table 11-7. DiffServ Statistics Commands CLI Command show diffserv service brief Description Displays all interfaces in the system to which a DiffServ policy has been attached. Class of Service The Class of Service (CoS) queueing feature lets you directly configure certain aspects of switch queueing. This provides the desired QoS behavior for different types of network traffic when the complexities of DiffServ are not required. The priority of a packet arriving at an interface can be used to steer the packet to the appropriate outbound CoS queue through a mapping table. CoS queue characteristics that affect queue mapping, such as minimum guaranteed bandwidth, transmission rate shaping, etc., are user-configurable at the queue (or port) level. Seven queues per port are supported. Although the hardware supports eight queues, one queue is always reserved for internal use by the stacking subsystem. To display the page, click Quality of Service →Class of Service in the tree view. The Class of Service menu page contains links to the following features: • Mapping Table Configuration • Interface Configuration • Interface Queue Configuration Mapping Table Configuration Each port in the switch can be configured to trust one of the packet fields (802.1p, IP Precedence, or IP DSCP), or to not trust any packet's priority designation (untrusted mode). If the port is set to a trusted mode, it uses a mapping table appropriate for the trusted field being used. This mapping table indicates the CoS queue to which the packet should be forwarded on the appropriate egress port(s). Of course, the trusted field must exist in the packet for the mapping table to be of any use, so there are default actions performed when this is not the case. These actions involve directing the packet to a specific CoS level configured for the ingress port as a whole, based on the existing port default priority as mapped to a traffic class by the current 802.1p mapping table. Alternatively, when a port is configured as untrusted, it does not trust any incoming packet priority designation and uses the port default priority value instead. All packets arriving at the ingress of an untrusted port are directed to a specific CoS queue on the appropriate egress port(s), in accordance with the configured default priority of the ingress port. This process is also used for cases where a trusted port mapping is unable to be honored, such as when a non-IP packet arrives at a port configured to trust the IP DSCP value. Use the Mapping Table Configuration page to define how class of service is assigned to a packet. To display the page, click Quality of Service →Class of Service →Mapping Table Configuration in the tree view. Configuring Quality of Service 701