Nortel Remote Gateway 9150 Installation And Administration Manual page 61

June 2005
Automatically switch from the IP network to the PSTN when the voice QoS
on the IP network falls below a predetermined threshold, and back to the IP
network when the QoS returns to normal.
Packetized voice
DSPs located in the Remote Gateway 9150 unit convert voice into digital data
packets and, if compression is used, compresses them. The data is constructed as
UDP/IP voice packets for transmission over the IP network.
When voice packets are compressed, they consume less bandwidth, leaving
more bandwidth for data or other voice or fax communications. The following
algorithms are supported:
G.711: Packets are transmitted at 64 Kbps (that is, they are not
compressed).
G.726: Packets are compressed and transmitted at 32 Kbps.
G.729A: Packets are compressed and transmitted at 8 Kbps.
G.729A is the default algorithm on both the RLC and the Remote Gateway 9150
unit.
In addition to voice compression, the Remote Gateway 9150 unit supports the
following additional packetized voice features:
A voice jitter attenuation buffer removes the variable delays from the voice
packets sent across the IP network, thus avoiding awkward-sounding
speech.
Packet loss handling techniques accommodate missing packets or packets
received too late to be processed.
Silence suppression prevents packet transmission during periods when
there is no voice data present. Comfort noise is inserted to assure the user
that the line is still active.
Silence is determined when the difference between the adaptable noise
floor and the detected signal is less than 9 dB. To prevent clipping, silence
must be present for a minimum of 250 milliseconds.
Remote Gateway 9150 Installation and Administration Guide
Remote Gateway 9150 description
33