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Quality of Service 191

IP Telephony Configuration Guide

Business Communications Manager router QoS support

With a Business Communications Manager system, the VoIP gateway and the router are in the

same box. The Business Communications Manager router performs QoS and priority queuing to

support VoIP traffic. The router supports VoIP in the following two ways:

• In a DiffServ network, the Business Communications Manager system acts as a DiffServ edge

device and performs packet classification, prioritization, and marking. The router performs

admission control for H.323 flows based on the WAN link bandwidth and utilization. When

received, the WAN link marks the H.323 flows as Premium traffic and places the flows in the

high priority queue.

• In a non-DiffServ or a legacy network, the router manages the WAN link to make sure

Premium VoIP packets have high priority in both directions when crossing a slow WAN link.

Network Quality of Service

This section discusses the quality of service aspects of networking.

• “Network monitoring” on page 192

• “Quality of Service parameters” on page 192

• “Fallback to PSTN” on page 193

Business Communications Manager VoIP Gateway uses a method like the ITU-T

Recommendation G.107, the E-Model, to determine the voice quality. This model evaluates the

end-to-end network transmission performance and outputs a scalar rating “R” for the network

transmission quality. The packet loss and latency of the end-to-end network determine “R”. The

model correlates the network objective measure “R”, with the subjective QoS metric for voice

quality, MOS or the Mean Opinion Score.

This model provides an effective traffic building process by activating the Fallback to

Circuit-Switched Voice Facilities feature at call set up to avoid quality of service degradation.

New calls fall back when the configured MOS values for all codecs are below the threshold.

The model is the reason for compression characteristics of the codecs. Each codec delivers a

different MOS for the same network quality.

Note: Differentiated Service (DiffServ) is a QoS framework standardized by the Internet

Engineering Task Force (IETF).

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Avaya IP Telephony Guía de configuración Pagina 191