Cisco WS-X4604-GWY - VoIP Gateway Especificaciones descargar pdf (Pagina 176)

Chapter 8 Quality of Service

Campus QoS Model

8-2

Cisco IP Telephony Network Design Guide

78-11103-03

Campus QoS really involves two separate areas of configuration, which are

discussed in the following sections:

• Traffic Classification

• Interface Queuing

Traffic Classification

Classifying or marking traffic as close to the edge of the network as possible has

always been an integral part of the Cisco network design architecture. Traffic

classification is an entrance criterion for access into the various queuing schemes

used within the campus switches and WAN interfaces. When connecting an IP

phone using a single cable model, the phone becomes the edge of the managed

network. As such, the IP phone can and should classify traffic flows. Table 8-1

lists the AVVID traffic classification guidelines.

Interface Queuing

To guarantee voice quality, it is a design requirement to enable QoS within the

campus infrastructure. By enabling QoS on campus switches, you can configure

all voice traffic to use separate queues, thus virtually eliminating the possibility

of dropped voice packets when an interface buffer fills instantaneously.

Although network management tools may show that the campus network is not

congested, QoS tools are still required to guarantee voice quality. Today’s

network management tools show only the average congestion over a sample time

span. While useful, this average does not show the congestion peaks on a campus

interface. Transmit interface buffers within a campus tend to congest absolutely

Table 8-1 Traffic Classification Guidelines for AVVID Networks

Traffic Type

Layer 2 Class of

Service (CoS)

Layer 3

IP Precedence Layer 3 DSCP

Voice RTP55EF

Voice Control 3 3 AF31

Video44AF41

Data 0-2 0-2 0-AF23

1 2 ... 171 172 173 174 175 176 177 178 179 180 181 ... 261 262

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Cisco WS-X4604-GWY - VoIP Gateway Especificaciones Pagina 176