Avaya IP Telephony Guia de Configuração descarregar pdf (Página 128)

128 Quality of Service

P0937663 03.1

Other measurement considerations

The Ping statistics described above measure the intranet before IP telephony installation. The

measurement does not take into consideration the expected load provided by the IP telephony

users.

If the intranet capacity is tight and the IP telephony traffic important, the installer or administrator

must consider making intranet measurements under load. Apply load using traffic generator tools;

the amount of load must match the IP telephony offered traffic estimated in the Business

Communications Manager VoIP Gateway Bandwidth requirements.

Decision: does the intranet meet IP telephony QoS needs?

The end of the measurement and analysis is a good indicator of whether the corporate intranet can

deliver acceptable voice and fax services. The Expected QoS level column in Table 23 on page

127 indicates to the installer or administrator the QoS level for each site pair with the data.

To provide voice and fax services over the intranet, keep the network within a Good or Excellent

QoS level at the Mean+σ operating area. Fax services must not travel on routes that have Fair or

Poor QoS levels.

If QoS levels of some or all routes fall short of being Good, evaluate options and costs for

upgrading the intranet. The evaluation often requires a link upgrade, a topology change, or

implementation of QoS in the network.

To maintain costs, you can accept a Fair QoS level for the time for a selected route. A calculated

trade-off in quality requires the installer or administrator to monitor the QoS level, reset needs

with the end users, and respond to user feedback.

Implementing QoS in IP networks

Corporate intranets are developed to support data services. Accordingly, normal intranets are

designed to support a set of QoS objectives dictated by these data services.

When an intranet takes on a real-time service, users of that service set additional QoS objectives in

the intranet. Some of the targets can be less controlled compared with the targets set by current

services, while other targets are more controlled. For intranets not exposed to real-time services in

the past, but which but now need to deliver IP telephony traffic, QoS objectives for delay can set

an additional design restriction on the intranet.

One method is to subject all intranet traffic to additional QoS restrictions, and design the network

to the strictest QoS objectives. An exact plan for the design improves the quality of data services,

although most applications cannot identify a reduction of, say, 50 ms in delay. Improvement of the

network results in a network that is correctly planned for voice, but over planned for data services.

Another plan is to consider using QoS in the intranet. This provides a more cost-effective solution

to engineering the intranet for non-homogenous traffic types.

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Avaya IP Telephony Guia de Configuração Página 128