Just a follow on to all the excellent answers.
First of all analog Voice has a frequency range upto 3400Hz.
In order to convert the analog voice to a digital we use PCM (analog / digital
conversion). The voice signals will need to subjected by a process
known as sampling, quantisation and encoding (binary level).
As speech is 3400Hz the sampling rate is 8000Hz. The encoding generates
8 bits of information.
A TDM E1.0 system has 32 Time Slots. Time slot 16 is used for signalling (by
convention) and Time Slot 0 (zero) is used for synchronisation and Frame alignment.
From the mathematics:-
– 32 Time Slots * 8 (bit encoding) = 256bits
– 8000Hz * 256bits = 2.048MB/s.
This also explains why a E1.0 link is know as a 2M link / connection.