S0 bus

What is an S0 interface?
An S0 interface (sometimes also called an S interface or S0 bus) allows traditional telephone users to connect to the Integrated Services Digital Network (ISDN) and place calls over the Public-Switched Telephone Network (PSTN). It is is similar to a router or modem that allows users to connect to the Internet, except that it provides connectivity into the traditional telephone network instead. 

Note: Even though ISDN is digital, it does not make use of the internet.

Are S0 interfaces secure?

S0 interfaces and ISDN were developed in the 1980s, when voice and data security were not as critically important as they are today. Neither of these technologies uses data encryption, which creates potential security vulnerabilities and increases the risk of data breaches. The lack of security with SO interfaces and ISDN are in stark contrast to Voice-over-IP (VoIP) technology, which uses advanced encryption methods to protect voice calls routed over the internet.

Why might companies want to keep their S0 interfaces?

If you are ready to switch to VoIP but still want to keep your existing ISDN technology, you can use a router with an S0 interface built in. This may help you extend returns on legacy telephony investments, but there are some known issues to be aware of, including poor or unreliable functioning of fax machines.

Do S0 interfaces have a future?

No, not really. With the internet able to route voice calls worldwide, there is no longer any need for the PSTN or for ISDN technology that routes calls across it. As a result, ISDN is being decommissioned across Europe in favour of all-IP telephony solutions and standards and, when that happens, S0 interfaces will become redundant as well. 

The benefits of migrating from ISDN to all-IP include lower calling costs, simpler telephony services and reduced in-house hardware, software and support requirements. 

For more information about VoIP and telephony in the cloud, enabled by technology such as the NFON Cloud Telephony System, please refer to the articles below: 


Further information

Voice over Internet Protocol (VoIP)

What is VoIP?

The Voice over Internet Protocol, also called IP telephony, is a method of communication for making calls over a broadband Internet connection as an alternative to regular calls made…

Read more

Integrated Services Digital Network (ISDN)

In telecommunications technology, the abbreviation ISDN stands for the technical term "Integrated Services Digital Network" and refers to a digital standard for telephone networks. As the name…

Read more