2N VoiceBlue Lite - Manual v2.6 - Manual (Page 44)

• G.711 – this codec us used in digital telephone networks. The
Pulse Code Modulation (PCM) is used for speech signal
coding. The sampled signal is coded by 12 bits and then
compressed to resultant 8 bits using a transformation
characteristic. The A-law compression is used in Europe, and
μ-law compression in North America and Japan. The resultant
data flow is 64 kbps.
• G.726 – this codec uses the Adaptive Differential Pulse Code
Modulation (ADPCM). This algorithm provides compression
of 8-bit samples of codec G.711 into 2, 3, 4 and 5-bit samples
with the resultant transmission rate of 16, 24, 32 and 40 kbps.
• G.729 – this codec uses the Conjugate-Structure Algebraic-
Code-Excited Linear-Prediction (CS-ACELP) with the
resultant transmission rate of 8 kbps. The speech signal is split
up into blocks of 10 ms each. The parameters of these blocks
are then entered into frames of the size of 10 bytes. 2 byte
frames are generated for noise transmission.
• G.723.1 – this codec uses the Multipulse Maximum Likelihood
Quantisation (MP-MLQ). The voice signal is split up into 30
ms blocks and coded into 24 byte frames with the resultant data
flow of 6.3 kbps. Another coding algorithm is the Algebraic
Code-Excited Linear Prediction (ACELP), which provides
coding of 30 ms blocks of speech into 20 byte frames with the
resultant transmission rate of 5.3 kbps. 4 byte frames are used
for noise transmission.
During call establishing, a codec is selected automatically for
voice transmission. 2N - VoiceBlue Lite is ready to use any of the
codecs included in Tab. 3.
The type of coding depends on your
VoIP network (terminals) and VoiceBlue Lite GSM gateway
configuration. The primary purpose of 2N - VoiceBlue Lite is to
provide connection to corporate VoIP networks and it tries to meet
the opposite side's codec requirements. If a codec incompatible
with VoiceBlue Lite is required, the call is rejected.
The IETF SIP and ITU-T H.323 protocols are mostly used for
making, maintaining and terminating connections. The
2N - VoiceBlue Lite gateway uses the SIP (Session Initiation
Protocol).
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