> For the complete documentation index, see [llms.txt](https://prosbcdocs.telcobridges.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prosbcdocs.telcobridges.com/telecom-references/isdn-and-cas/pstn.md).

# PSTN

The Public-Switched Telephone Network, or PSTN, refers to the traditional phone network before the advent of IP-based telephony. It is based on [TDM](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/transmission/tdm/README.md) technology, uses [SS7](https://telcobridges.com/media-gateways/solutions/signaling/migrating-ss7-sigtran/), [ISDN](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/isdn/README.md) or [CAS](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/cas/README.md) for signaling and [PCM](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/pcm/README.md) for voice encoding.

### TelcoBridges and the PSTN

TelcoBridges' entire product line supports the PSTN. [Tmedia](https://telcobridges.com/media-gateways/products/tmedia-gateways/) and [Tdev](https://telcobridges.com/products/development-platforms-tdev/) devices can perform tandem-switching, signaling conversion (between SS7, ISDN, and CAS), [call routing](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/concepts/call-routing/README.md), [trunking](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/sip-voip/trunking/README.md) and more. They can also intermediate between the PSTN and IP telephony devices, performing activities typical of a media gateway, such as [transcoding](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/voice-media/transcoding/README.md) and switching.

### References

* [Wikipedia article](http://en.wikipedia.org/wiki/Public_switched_telephone_network)


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