PSTN, which stands for Public Switched Telephone Network, is the traditional telephone network that first facilitated calls across the UK in 1875.
It’s connected across the UK by nearly 5,600 telephone exchanges.
The ISDN network was added to the PSTN by BT in 1986. Its purpose was to transmit data that the PSTN couldn’t facilitate previously, like video calls.
BT has not installed any new ISDN lines in central London since 2014. This fact alone goes to show that many businesses have already moved on.
Exactly 150 years after PSTN was introduced, BT Openreach decided that the equipment is too old to stay in use. The company has already begun work on upgrading the old copper wires that currently make up the PSTN.
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