What are MSNs?
Multiple Subscriber Numbers (MSNs) relate to the Integrated Digital Services Network (ISDN). They allow users to allocate different phone numbers to different devices within the network. Like a landline, a complete MSN consists of a country and area code followed by the MSN number.


What is ISDN?

ISDN is the technology that brought digital functionality to the traditional phone network, otherwise known as the Public-Switched Telephone Network (PSTN). In particular, ISDN enables the simultaneous transmission of different types of data, such as voice and video, over the PSTN. 

In the near future, ISDN will be decommissioned across Europe in favour of voice-over-IP (VoIP) technology, which routes phone calls across the internet rather than the PSTN. In the UK, BT has already announced that ISDN will be decommissioned in the next few years, while the date set for decommissioning in Germany is 2018. VoIP technology is far more efficient and cost-effective than ISDN, which is one of the main reasons it is being decommissioned.

What are MSNs used for?

MSNs are used to ensure that every device on the network has a different phone number. Additionally, they allow users to make two voice calls simultaneously over a single ISDN connection. When a phone call enters the ISDN network, it is delivered to the specific MSN via the S0 bus.

NOTE: One device can have multiple MSN numbers allocated to it.

How does placing calls an MSN compare with VoIP?

[Translate to UK:]VoIP solutions such as the NFON Cloud Telephone System are much more flexible than MSNs. This is because MSNs are static numbers that are allocated to fixed points in the network, whereas VoIP connections allow users to log in from anywhere, using any device. 

This means that with MSNs, employees visiting different offices are not able to use their own phone numbers and can only communicate using local numbers at that office. With VoIP, they can simply log into the remote office network and use their own phone number to contact colleagues or customers.

For more information about MSNs and other telephone technologies, or to discover the benefits of the NFON Cloud Telephone System, please review the articles below: 


Further information


A telephone connection is a standard part of telecommunications. In the following, we will first take a closer look at the term.

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Voice over IP: The Art of Switching from PSTN to IP

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…

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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…

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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…

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