# What is the PSTN?

> The PSTN (Public Switched Telephone Network) is the traditional circuit-switched telephone network of landlines, exchanges, and interconnects that predates VoIP. Programmable voice and SIP trunking reach it through PSTN termination and origination, so a call placed by an API can ring any ordinary phone number and inbound calls from landlines can reach an application. Much of the PSTN core is now IP, but the numbering plan and reach it represents remain central to voice. See /answers/voice-api-sip-trunking, /answers/what-is-did, and /products/voice.

- Canonical URL: https://www.broadnet.me/answers/what-is-pstn
- Language: en
- Last reviewed: 2026-07-22
- Publisher: BroadNet (https://www.broadnet.me)

## Related

- [All answers](https://www.broadnet.me/answers)
- [Glossary](https://www.broadnet.me/answers)
- [How does a voice API and SIP trunking work?](https://www.broadnet.me/answers/voice-api-sip-trunking)
- [What is a DID (Direct Inward Dialing) number?](https://www.broadnet.me/answers/what-is-did)
- [What is SIP (Session Initiation Protocol)?](https://www.broadnet.me/answers/what-is-sip)
- [How does programmable voice work?](https://www.broadnet.me/answers/programmable-voice)
- [Voice](https://www.broadnet.me/products/voice)