PTSN and ISDN 2025 shutdown

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BT is forging ahead with plans to shut its traditional telephone network in the UK, with the intention of moving all customers over to IP telephony services by 2025.

The closure of the public switched telephone network (PSTN) and Integrated Services Digital Network (ISDN) is part of plans by BT for Internet based voice calls via the fibre network.

What is PSTN?

The Public Switched Telephone Network (PSTN) are landline telephony systems that you have in your home and some businesses. With calls made via PSTN, analogue voice data travels over copper phone lines that are owned and operated by BT. This is dated technology, built upon the original systems used for the first public phone networks.

Asymmetric Digital Subscriber Line (ADSL) and Fibre to The Cabinet (FTTC) are both types of Broadband that run on copper lines. BT have not stated that they will be stopping Broadband traversing these lines, it will just be the case that they will just be ceasing analogue voice data communication.

What is ISDN?

Integrated Services Digital Network (ISDN) was introduced thirty years ago which allowed digital transmission of voice, video and other services simultaneously. ISDN uses the traditional PSTN network to perform this, however it differs in that it offers both voice and data services delivered simultaneously.

What’s the reason for them being switching off?

PSTN and ISDN are dated technology, they are no longer the most productive options and hinder Internet connectivity. Maintaining legacy networks is also extremely costly.

Internet Protocol (IP) lines can cover all services (voice, data, video, and broadcasting), this means BT only have to maintain one network. The recent investment and nationwide roll out of Superfast Fibre and new Ethernet products provide a considerable improvement over PSTN and ISDN networks.

What will they be replaced with?

SIP Trunks

Session Initiation Protocol (SIP) trunking will replace ISDN lines by default. With SIP trunking businesses require an Internet connection and a phone system.


Voice over Internet Protocol (VoIP) allows you to make and receive phone calls through your Internet connection. SIP trunks can carry all forms of media including voice, data, and video.

Cloud Hosted Telephony

Cloud telephony is a managed service we offer that enables your business flexibility, your phone system is hosted and managed in the Cloud. Meaning less equipment and initial outlay, reduced maintenance costs, mobility, more features and built in Disaster Recovery.

Hosted VoIP has many advantages over PSTN and ISDN

– Much quicker to have a new line

– Less physical lines required, resulting in a reduction of line rental costs

– Flexibility and scalability

– Have a number for any region or country

– Use your phone number anywhere you have an Internet connection

What is the biggest difference?

The biggest difference between ISDN and SIP networks for organisations is the cost. Communications between SIP users can be completely free, regardless of the location. VoIP starts with a fixed cost for a phone number and extensions on a provider’s network (SIP trunk). Unlike traditional phone systems where you are paying multiple times to be connected, you only pay for call termination charges with VoIP.

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