Bandwidth Requirements in VoIP Effect of VAD
This topic describes the effect of voice activity detection (VAD) on total bandwidth.
On average, an aggregate of 24 calls or more may contain 35 percent silence. With traditional telephony voice networks, all voice calls use 64-kbps fixed-bandwidth links regardless of how much of the conversation is speech and how much is silence. With Cisco VoIP networks, all conversation and silence is packetized. VAD suppresses packets of silence. Instead of sending VoIP packets of silence, VoIP gateways interleave data traffic with VoIP conversations to more effectively use network bandwidth.
VAD provides a maximum of 35 percent bandwidth savings based on an average volume of more than 24 calls.
Note Bandwidth savings of 35 percent is an average figure and does not take into account loud background sounds, differences in languages, and other factors.
The savings are not realized on every individual voice call, or on any specific point measurement.
Note For the purposes of network design and bandwidth engineering, VAD should not be taken into account, especially on links that will carry fewer than 24 voice calls simultaneously.
Various features, such as music on hold (MOH) and fax, render VAD ineffective. When the network is engineered for the full voice call bandwidth, all savings provided by VAD are available to data applications.
VAD is enabled by default for all VoIP calls. VAD reduces the silence in VoIP conversations but it also provides comfort noise generation (CNG). Because you can mistake silence for a disconnected call, CNG provides locally generated white noise to make the call appear normally connected to both parties.
Continue reading here: Configuring Auxiliary VLANs
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