Key Voip Concepts - Nortel BCM50 Configuration Manual

LAN
A Local Area Network (LAN) is a communications network that serves users within a confined
geographical area. For BCM, a LAN is any IP network connected on the BCM system. Often, the
LAN can include a router that forms a connection to the Internet. A BCM can have up to two LAN
connections.

Key VoIP concepts

The following explains a few commonly used VoIP terms.
QoS
QoS (Quality of Service) is technology that determines the maximum acceptable amount of
latency, and balances that with the quality of the VoIP connection. BCM and network routers use
QoS to ensure that real time critical IP packets, such as voice packets, are given higher routing and
handling priority than other types of data packets.
Silence suppression
Silence suppression technology identifies the periods of silence in a conversation, and stops
sending IP speech packets during those periods. Telco studies show that in a typical telephone
conversation, only about 36% to 40% of a full-duplex conversation is active. When one party in
the conversation is quiet for more than a few hundredths of a second, voice packet transmission is
suppressed until the party starts talking again. This is half-duplex. There are important periods of
silence during speaker pauses between words and phrases. By applying silence suppression,
average bandwidth use is reduced by the same amount. This reduction in average bandwidth
requirements develops over a 20-to-30-second period as the conversation switches from one
direction to another. Refer to
Codecs
The algorithm used to compress and decompress voice over IP networks and VoIP trunks is
embedded in a software entity called a codec (COde-DECcode).
Refer to "Codec rates" on page 549
rates.
• The G.711 Codec samples the voice stream at a rate of 64 kbps (kilo bits per second), and is
the Codec to use for maximum voice quality. Choose the G.711 Codec with the companding
law (alaw or ulaw) that matches your system requirements.
• The G.729 Codec samples the voice stream at 8 kbps. The voice quality is slightly lower using
a G.729 but it reduces network traffic by approximately 80%.
• The G.723 Codec should be used only with third party devices that do not support G.729 or
G.711.
"Silence suppression" on page
for a listing of the supported codes and their transmission
Chapter 42 VoIP overview
529.
Networking Configuration Guide
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