GS-4012F User’s Guide
Chapter 28 Differentiated Services
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28
Differentiated Services
This chapter shows you how to configure Differentiated Services (DiffServ) on the switch.
28.1 Overview
Quality of Service (QoS) mechanisms provide the best service on a per-flow guarantee. To
fine-tune the levels of services on the priority of the traffic flow using QoS places a heavy
burden on the network infrastructure.
DiffServ is a class of service (CoS) model that marks packets so that they receive specific per-
hop treatment at DiffServ-compliant network devices along the route based on the application
types and traffic flow. Packets are marked with DiffServ Code Points (DSCPs) indicating the
level of service desired. This allows the intermediary DiffServ-compliant network devices to
handle the packets differently depending on the code points without the need to negotiate
paths or remember state information for every flow. In addition, applications do not have to
request a particular service or give advanced notice of where the traffic is going.
28.1.1 DSCP and Per-Hop Behavior
DiffServ defines a new DS (Differentiated Services) field to replace the Type of Service (ToS)
field in the IP header. The DS field contains a 2-bit unused field and a 6-bit DSCP field which
can define up to 64 service levels. The following figure illustrates the DS field.
DSCP is backward compatible with the three precedence bits in the ToS octet so that non-
DiffServ compliant, ToS-enabled network device will not conflict with the DSCP mapping.
Figure 76
DiffServ: Differentiated Service Field
The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior), that each
packet gets across the DiffServ network. Based on the marking rule different kinds of traffic
can be marked for different priorities of forwarding. Resources can then be allocated
according to the DSCP values and the configured policies.
28.1.2 DiffServ Network Example
The following figure depicts a simple DiffServ network consisting of a group of contiguous
DiffServ-compliant network devices.
DSCP (6 bits)
DS (2 bits)
Summary of Contents for GS-4012F
Page 1: ...GS 4012F Ethernet Switch User s Guide Version 3 60 4 2005...
Page 19: ...GS 4012F User s Guide 18 Table of Contents...
Page 25: ...GS 4012F User s Guide 24 List of Figures...
Page 29: ...GS 4012F User s Guide 28 List of Tables...
Page 39: ...GS 4012F User s Guide 38 Chapter 1 Getting to Know Your Switch...
Page 43: ...GS 4012F User s Guide 42 Chapter 2 Hardware Installation and Connection...
Page 49: ...GS 4012F User s Guide 48 Chapter 3 Hardware Overview...
Page 63: ...GS 4012F User s Guide 62 Chapter 5 Initial Setup Example...
Page 69: ...GS 4012F User s Guide 68 Chapter 6 System Status and Port Statistics...
Page 101: ...GS 4012F User s Guide 100 Chapter 11 Spanning Tree Protocol...
Page 113: ...GS 4012F User s Guide 112 Chapter 15 Link Aggregation...
Page 117: ...GS 4012F User s Guide 116 Chapter 16 Port Authentication...
Page 125: ...GS 4012F User s Guide 124 Chapter 18 Classifier Figure 53 Classifier Example...
Page 131: ...GS 4012F User s Guide 130 Chapter 19 Policy Rule Figure 56 Policy Example...
Page 135: ...GS 4012F User s Guide 134 Chapter 20 Queuing Method...
Page 141: ...GS 4012F User s Guide 140 Chapter 21 VLAN Stacking...
Page 183: ...GS 4012F User s Guide 182 Chapter 30 VRRP...
Page 203: ...GS 4012F User s Guide 202 Chapter 32 Access Control...
Page 205: ...GS 4012F User s Guide 204 Chapter 33 Diagnostic...
Page 219: ...GS 4012F User s Guide 218 Chapter 38 Routing Table...
Page 267: ...GS 4012F User s Guide 266 Chapter 40 Command Examples...
Page 277: ...GS 4012F User s Guide 276 Chapter 41 IEEE 802 1Q Tagged VLAN Commands...
Page 287: ...GS 4012F User s Guide 286 Chapter 42 Troubleshooting...
Page 291: ...GS 4012F User s Guide 290 Product Specifications...