Zyxel GS2200-24 Руководство пользователя онлайн [240/332] 810932

GS2200-8/24 User’s Guide 240

CHAPTER 31

Differentiated Services

31.1 Overview

This chapter shows you how to configure Differentiated Services (DiffServ) on the Switch.

Quality of Service (QoS) is used to prioritize source-to-destination traffic flows. All packets in the

flow are given the same priority. You can use CoS (class of service) to give different priorities to

different packet types.

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.

31.1.1 What You Can Do

•Use the DiffServ screen (Section 31.2 on page 241) to activate DiffServ to apply marking rules

or IEEE 802.1p priority mapping on the Switch.

•Use the DSCP screen (Section 31.3.1 on page 242) to change the DSCP-IEEE 802.1p mapping.

31.1.2 What You Need to Know

Read on for concepts on Differentiated Services that can help you configure the screens in this

chapter.

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 6-bit DSCP field which can define up to 64 service levels and

the remaining 2 bits are defined as currently unused (CU). The following figure illustrates the DS

field.

Figure 153 DiffServ: Differentiated Service 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.

DSCP (6 bits) CU (2 bits)