Dell PowerConnect 8100 CLI Reference Guide - Page 635

QoS Commands 31 Quality of Service (QoS) technologies are intended to provide guaranteed timely delivery of specific application data to a particular destination. In contrast, standard IP-based networks are designed to provide best effort data delivery service. Best effort service implies that the network delivers the data in a timely fashion, although there is no guarantee. During times of congestion, packets may be delayed, sent sporadically, or dropped. For typical Internet applications, such as electronic mail and file transfer, a slight degradation in service is acceptable and, in many cases, unnoticeable. Conversely, any degradation of service has undesirable effects on applications with strict timing requirements, such as voice or multimedia. QoS is a means of providing consistent, predictable data delivery by distinguishing between packets that have strict timing requirements from those that are more tolerant of delay. Packets with strict timing requirements are given special treatment in a QoS-capable network. To accomplish this, all elements of the network must be QoS-capable. If one node is unable to meet the necessary timing requirements, this creates a deficiency in the network path and the performance of the entire packet flow is compromised. Access Control Lists The PowerConnect ACL feature allows classification of packets based upon Layer 2 through Layer 4 header information. An Ethernet IPv6 packet is distinguished from an IPv4 packet by its unique Ether-type value; thus, all IPv4 and IPv6 classifiers include the Ether-type field. Multiple ACLs per interface are supported. The ACLs can be combination of Layer 2 and/or Layer 3/4 ACLs. ACL assignment is appropriate for both physical ports and LAGs. QoS Commands 635