2.2.5.2. Sampling Time 
Voice needs to be digitized before it can be assembled into IP packets.
For telephony applications, voice is sampled every 125 μs at 8bits.
It would not make sense to package each individual 8 bit sample into
an IP packet. Instead, for G.711 encoding at least 240 8 bit samples
are combined into an IP packet.
It takes 30 ms to acquire 240 voice samples.
The Sampling Time is defined as the time it takes to sample a specified
number of voice samples that are sent out in one IP packet.
It is obvious that the longer the sampling time, the smaller the IP
overhead gets. Thus, in order to minimize bandwidth, the sampling time
will have to be increased.
However, increasing the sampling time will increase the overall delay!
IMPORTANT:
There is always a trade off between minimizing
the delay versus minimizing the required bandwidth.
For IP line gateways the sampling time can be set between 10 ms and
90 ms depending on codec type.