Port-Based And Role-Based Qos Policies; Qos Overview - Nortel 4524GT Configuration

18 Chapter 1 An Introduction to Policy-Enabled Networks
metering, and re-marking. You can specify a number of policies and each
policy can match one or many flows to support complex classification
scenarios.

Port-based and Role-based QoS Policies

Software Release 5.1 supports both port-based and role-based Quality of
Service policies. In a port-based Quality of Service environment, apply
policies directly to individual ports. In a role-based Quality of Service
environment, individual ports are first assigned to a role and that role is
assigned a policy.
A port-based Quality of Service environment provides more direct
application of Quality of Service policies and eliminates the need to group
ports when you assign policies.
You can apply port-based and role-based policies to the same port; however,
the switch administrator must divide resources across the individual policies.

QoS overview

Differentiated services (DiffServ) is a Quality of Service (QoS) network
architecture that offers various levels of service for different types of
data traffic. DiffServ designates a specific level of performance on a
packet-by-packet basis, instead of using the best-effort model for data
delivery. Preferential treatment (prioritization) can apply applications that
require high performance and reliable service, such as voice and video
over IP.
To differentiate between traffic flows, the DiffServ (DS) field, as defined
in RFCs 2474 and 2475, is marked. The DS field in the IP header is an
octet, and the DS architecture uses the first six bits, called the DS codepoint
(DSCP). The DSCP marking dictates the forwarding treatment given to
the packet at each hop. This marking occurs at the edge of the DiffServ
domain, and is based on the policy or filter for the particular microflow or an
aggregate flow. The QoS system also can interact with 802.1p and Layer
2 QoS.
Within the DiffServ network, the marked packets are placed in a queue
according to their marking, which, in turn, determines the per-hop behavior
(PHB) of that packet. For example, if a video stream is marked as high
priority, then it is placed in a high-priority queue. As those packets traverse
the DiffServ network, the video stream is forwarded before any other
packets.
To ensure that the traffic stream conforms to the bandwidth assigned,
policing within the network is necessary.
Copyright © 2007, Nortel Networks
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Nortel Ethernet Routing Switch 4500 Series
Configuration — Quality of Service
NN47205-504 (322816-B)
5.1 23 November 2007
03.01 Standard