PSTN stands for Public Switched Telephone Service.
In short, the PSTN is the copper infrastructure that has enabled telephony services across the UK since it was introduced in the 1800s. It is used by thousands of businesses and millions of homeowners to make and receive calls every single day. However, this aging infrastructure is becoming much more expensive and complicated to maintain. For this reason, all PSTN and ISDN services are currently in the process of being replaced by more futureproof, data-only alternatives. The switch off is due to reach completion in 2025, meaning all legacy solutions will need to be replaced by this date, if not before.
The deployment of an all-IP network means that traditional lines are due to become obsolete, and this extends to lift lines too.