[Q] Transmission frequency,

[wei]

Hi,
Maybe my question sounds stupid,
However, since we know that frequency is a property in analog communication.
So,
Digital communication has frequency as well (I beleive the answer is yes) ?
If so, what is the frequency of transmission in LAN, WAN or internet in general?

Thanks,

[wei]

To make clear my previous question:
Frequency I mean here is both carrier frequency. We know the bandwidth depends on each type of technology.

Thanks.

[dangquangminh]

wei,

Signal refers to a desired electrical voltage, light pattern, or modulated electromagnetic wave. All of these can carry networking data.

One type of signal is analog.

The two important characteristics of a sine wave are its amplitude (A) - its height and depth - and its period (T) - length of time to complete 1 cycle. You can calculate the frequency (f) - wiggleyness - of the wave with the formula f = 1/T.

Another type of signal is digital. A digital signal has the following characteristics:

- has discrete, or jumpy, voltage-versus-time graphs
is typical of technology, rather than nature

Digital signals have a fixed amplitude but their pulsewidth and frequency can be changed. Digital signals from modern sources can be approximated by a square wave, which has seemingly instantaneous transitions from low to high voltage states, with no wiggles.

Fourier synthesis:

A square wave, or a square pulse, can be built by using the right combination of sine waves. The main graphic shows how the square wave (digital signal) can be built with sine waves (analog signals). This is important to remember as you examine what happens to a digital pulse as it travels along networking media

For more information, check out the CCNA curriculum, chapter 4, semester I.

Cheers,
Minh