ZyXEL Communications P-660 series Guia do Utilizador descarregar pdf (Página 145)

P-660R-F1 Series User’s Guide 145

CHAPTER 11

Quality Of Service

11.1 Overview

Use the QoS screens to set up your ZyXEL Device to use QoS for traffic management.

Quality of Service (QoS) refers to both a network’s ability to deliver data with minimum delay, and

the networking methods used to control bandwidth. QoS allows the ZyXEL Device to group and

prioritize application traffic and fine-tune network performance.

Without QoS, all traffic data are equally likely to be dropped when the network is congested. This

can cause a reduction in network performance and make the network inadequate for time-critical

applications such as video-on-demand.

The ZyXEL Device assigns each packet a priority and then queues the packet accordingly. Packets

assigned with a high priority are processed more quickly than those with low priorities if there is

congestion, allowing time-sensitive applications to flow more smoothly. Time-sensitive applications

include both those that require a low level of latency (delay) and a low level of jitter (variations in

delay) such as Voice over IP (VoIP) or Internet gaming, and those for which jitter alone is a problem

such as Internet radio or streaming video.

11.1.1 What You Can Do in the QoS Screens

•Use the General screen to enable QoS on the ZyXEL Device, decide allowable bandwidth using

QoS and configure priority mapping settings for traffic that does not match a custom class.

•Use the Class Setup screen to set up classifiers to sort traffic into different flows and assign

priority and define actions to be performed for a classified traffic flow.

•Use the Monitor screen to view the ZyXEL Device’s QoS-related packet statistics.

11.1.2 What You Need to Know About QoS

QoS versus Cos

QoS is used to prioritize source-to-destination traffic flows. All packets in the same flow are given

the same priority. Class of Service (CoS) is a way of managing traffic in a network by grouping

similar types of traffic together and treating each type as a class. You can use CoS to give different

priorities to different packet types.

CoS technologies include IEEE 802.1p layer 2 tagging and Differentiated Services (DiffServ or DS).

IEEE 802.1p tagging makes use of three bits in the packet header, while DiffServ is a new protocol

and defines a new DS field, which replaces the eight-bit Type of Service (ToS) field in the IP header.

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ZyXEL Communications P-660 series Guia do Utilizador Página 145