CANOGA PERKINS CanogaOS Configuration Guide - Manual (Page 265)

CanogaOS Configuration Guide
Proprietary & Confidential Canoga Perkins Metro Ethernet Switches Page 265 of 350
31 Configuring QoS
31.1 QoS Overview
Quality of Service (QoS) can be used to give certain traffic priority over other traffic.
Without QoS, all traffic in a network has the same priority and chance of being delivered on
time. If congestion occurs, all traffic has the same chance of being dropped.
With QoS, specific network traffic can be prioritized to receive preferential treatment. In turn, a
network performs more predictably, and utilizes bandwidth more effectively.
31.1.1 QoS Functionality
Classification information can be carried in the Layer-3 IP packet header or the Layer-2 frame.
IP packet headers carry the information using 6 bits or 3 bits from the deprecated IP type of
service (TOS) field. Layer-2 802.1Q frames carry the information using a 2-byte Tag Control
Information field.
All switches and routers accessing the Internet depend on class information to give the same
forwarding treatment to packets with the same class information, and give different treatment to
packets with different class information. A packet can be assigned class information, as follows:
• end hosts or switches along a path, based on a configured policy
• detailed packet examination, expected to occur nearer to the network edge, to prevent
overloading core switches and routers
• a combination of the above two techniques
Class information can be used by switches and routers along a path to limit the amount of
allotted resources per traffic class.
Per-hop behavior is an individual device’s behavior when handling traffic in the DiffServ
architecture. An end-to-end QoS solution can be created if all devices along a path have
consistent per-hop behavior.
31.1.2 Terminology
Following is a brief description of terms and concepts used to describe QoS.
ACL
Access control lists (ACLs) classify traffic with the same characteristics. IP traffic is classified
using IP ACLs, and non-IP traffic is classified using MAC ACLs.
The ACL can have multiple access control entries (ACEs), which are commands that match
fields against the contents of the packet.
CoS Value