Innovation of Modern Digital Telecommunication

The word digital comes from English word digit where real world information like sounds or image is converted into a continuous sequence of binary numeric (0 & 1 digits). Digital technology breaks your voice into a series of 0s and 1s and transfers it to the other end where another phone receives all the numbers and reassembles them into original signal or voice.

The beauty of digital technology is that it allows to cram lots of those 0s and 1s into same space an analog signal uses before. That means it permits transferring many phone calls over the same copper cable used by the plain old telephone service (POTS) previously. With the advent of digital technology PSTN can now carry many independent calls simultaneously over a single cable.

In digital data transmission, each of these 0s and 1s represent 1 bit where 1024 bits equal to 1 kilobits. Any phone call is carried over the PSTN at a fixed rate of 64 kilobits per second (Kbps) in each direction from a calling party to a called party (So the total transmission counts 64*2= 128 Kbps).

If we represent 128 Kilobits to a higher unit it becomes 16 kilobytes (KB), since there are 8 kilobits in 1 kilobyte (128/8=16). So, in a typical 5 minutes circuit switched based PSTN conversation a total of 4800 KB (16*60*5=4800) data is transferred through the network which is roughly equals to 5 megabytes (1024 KB = 1 Megabyte).

If you ever download anything from internet to your personal computer, you will know that 5 MB is a considerably large file size to download. Packet-switched network has intervened in this regard to reduce the size of transmitted data.