VoIP: Voice over Internet Protocol ◾ 303
Coding Delay
e first requirement for transmitting voice as packets is coding. e function is to
convert analog voice to digital data (coding), and the device or software used to do
this is called the coder. e coder also performs voice compression. Traditionally, if
voice is sampled at 8 kHz, and each bit is represented by 8 bits, then the bandwidth
of the channel to carry the sampled speech without compression must be 64 kilo-
bits per second. Hence, one voice channel has capacity:
where f
s
is the sampling frequency and must be at least twice the highest frequency
content of voice (taken to be about 3.4 kHz), and Q is the quantization bits (num-
ber of bits per sample). Transmitting voice at