Network Evolution
In the past, networks tended to be designed specifically to carry voice, video, or data signals.
The design of voice, video, or data networks differed because of fundamental differences between voice, video, and data signals.
eg., voice is analog, data is digital in nature
The telephone network was the first and is by far the largest network supporting wired telephones, fax machines, cellular phones, cordless phones, answering machines, and modems (for data transmission over the phone network).