Data transfer at certain frequencies
Channel Capacity or maximum data rate is the maximum rate at which data can be transmitted over a given communication link, or channel.

In general, information is conveyed by change in values of the signal in time. So more the frequency of a signal, more is the achievable data rate.

For a communication channel,

Δf⋅Δt≈1

To transmit one signal, a pulse of length Δt (in time) is required. If one signal represents one bit, then the data rate is about 1/Δt. So the maximum data rate in bit/second is about the same as the band width Δf in Hertz. 

But this is an incredible underestimate of the information capacity of a transmission system. It assumes that you are sending rectangular shaped pulses.
Using different encoding schemes, more than one bit can be represented by one cycle of signal.

The channel capacity of a channel increases proportionally with the bandwidth. But in practice, we cannot keep increasing the signal bandwidth infinitely. Apart from this, there are other standard transmission constraints in the form of different channel noise sources that strictly limit the signal bandwidth to be used. According to Shannon Hartley equation, the only limit to data rate in a given bandwidth is, the Signal to Noise Ratio.

Using Shannon formula we can obtain an absolute limit of the maximum data transmission rate.

$C = B + log_2(1 + S/N)$

C - Channel capacity
B - Bandwidth
S - Average received signal power over the bandwidth
N - Average noise over the bandwidth