ISDN and PTSN are two of the oldest highly functional methods of voice data delivery. How do they differ?
PSTN is the older of the two and works by delivering voice data to the end user via copper wires (twisted), operating in both business and residential environments. Its core network is mostly analogue, though developments in recent years have upgraded it to be digital, almost entirely, though it still has the analogue system to the end user and from the exchange.
ISDN is the newer of the two and was developed as an improvement on the PSTN. It has the ability to deliver more than two connections over a single line simultaneously. It is completely digital, though a little outdated compared to the technology available today. Its digital nature allows it to transmit video, voice and fax data. Since it can host multiple connections over a single line, it is best suited for larger businesses.
Why would the two be compared?
The two are easily comparable because they seek to solve the same user problem, transmitting data from user to user. However, they use the same approach with their lines, the difference being that ISDN is fully digitized and supports transmission of multimedia data. It is also notable that ISDN makes calls faster than PSTN.
ISDN is definitely better than PSTN because it can host a larger number of lines and is easier to scale in addition to the fact that it is digitized fully, not just its core like PSTN. It can also transmit multimedia data, making it easily applicable today. However, like PSTN it is becoming outdated and may soon be obsolete, with users opting for options like hosted PBX and SIP trunking for organisational use in any scale.
Are PSTN phones still in use?
Yes they are. To this day, PSTN phones are still generally used as a form of standard communication. However, it would be important to remember that there has been a continuous and steady decline of the use of PSTN phones in the last decade, implying that they may soon be obsolete.