ISDN - 6 : Development
This playlist provides an overview of #ISDN (Integrated Services Digital Network) development and operation.
• 35 : ISDN - Fundamentals of Communications
To discuss the history and development of ISDN, we must first go back a little bit and explore the history of the telephone.
Originally, telephones were connected using analog signaling, but this became too inefficient as the number of phones grew. Eventually digital communication techniques were used to connect the main phone switches and offices. This was much more efficient and also offered a cleaner communication channel between switches. However, though the main phone switches and offices used digital connections, the place where the calls terminated, for example, your home, was still an analog connection. This means the final connection, often called "the last mile," was analog.
These kind of phone connections, which are both analog and digital, require your call to undergo several conversions between analog and digital as it travels from one end of the call to the other. Analog is used between the phone and the local switch. Then analog is converted to digital to travel between phone company switches, then, finally, converted back to analog when it's sent to the receiving phone.
It's even more complicated when a computer is used. The computer communicates to the modem digitally, the modem communicates to the first switch using analog, then the switch uses digital communication, then it's back to analog to the modem and finally back to digital to the computer.
ISDN was designed to improve this process. Using ISDN, you replace the analog local loop (or connection) with a digital ISDN connection. This way, all communication - whether it is voice, video, or data - stays digital from end-to-end.
Digital communication is easier to multiplex, easier to repeat, and easier to keep clean, meaning it has much less signal noise, so using digital is favored over analog.