Which SIP is best for long-term investments

ISDN telephone systems - shutdown & alternatives

According to estimates by the Federal Network Agency, around 11.63 million ISDN basic connections and 19.67 million analogue telephone systems were still in use in 2010, but the number of analogue and ISDN telecommunications systems has now decreased significantly. The number of analog and ISDN telephone connections did not even reach 1 million in 2019. As a result, a central change in telecommunications is also reflected in Germany: the switch to All-IP. Many companies still rely on ISDN-based telephony, especially in the business environment - at the same time, the switch-off of ISDN in the context of the switch to IP telephony is in full swing. So now is the time to act and investing in a future-proof form of telephony forms the basis for efficient corporate communication. Find out now about all the necessary facts about disconnecting ISDN, practical interim solutions and long-term alternatives to an ISDN telephone system using VoIP telephony.

Switching off ISDN - is an ISDN telephone system still worthwhile?

The answer to the question of whether it is still worth installing a new ISDN telephone system is clearly “no”. The switch to virtual all-IP technologies began in 2018, which means that more and more providers are reducing their range of ISDN PBXs and from now on rely on modern types of telephony, such as VoIP or cloud telephony. The schedule for the shutdown of ISDN varies depending on the provider, but it can generally be stated that it is There will be no more ISDN connections by 2022 at the latest. The orientation towards All-IP is directional and future-oriented, which means that expensive investments in outdated ISDN telephony are not advisable.

Advantages of the ISDN PBX

  • Excellent voice quality
  • High data security
  • Two voice channels so that parallel conversations can be held
  • Large number of phone numbers

Disadvantages of the ISDN PBX

  • ISDN is being phased out: ISDN will be switched off by 2022 at the latest
  • Costly purchase + technician required for installation
  • Service and maintenance effort: difficult procurement of spare parts after shutdown
  • Service and maintenance costs ➞ for rather less suitable
  • Finite number of phone numbers (99) ➞ makes expansion of the ISDN system difficult

Switching off ISDN - what does the switch to All-IP mean?

ISDN PBXs have long been considered the operational standard for telecommunications. With the increasing importance of digital data transmission over the Internet, the requirements for telephone systems also changed, as a result of which the number of analog and ISDN-based telephone connections began to decline. Currently, providers such as Telekom or Vodafone are gradually switching off their ISDN connections and replacing them with virtual telephone systems.

The change towards Internet telephony is also generally summarized under the term “All-IP”. “IP” stands for Internet Protocol and describes the digital form of data transmission over the Internet, which enables technologies such as Voice over IP telephony. All-IP is the conversion of the transmission technology to the Internet Protocol (IP).

Where previously different ways of transmitting data were used with mobile communications or cable television, All-IP describes the combined transmission of all data over the Internet. The future of telecommunications thus lies in Next Generation Network (), which represents a comprehensive infrastructure for the transmission of data over the Internet.

The great advantage here is that only a network or an Internet connection is required to use services such as telephony, mobile communications, Internet or fax. All-IP has replaced analog and ISDN-based telephony and combines previously differently transmitted data streams in one network - the NGN. Since only a single Internet connection is required, there is no need to use a separate ISDN connection.

This is how the transition works successfully: 5 tips for your company

  • Note contractual obligations: Check your current contracts and terminate them in good time - if you haven't already done so - in order to avoid double costs. These can be service or provider contracts, for example, that you no longer need after switching to All-IP. Do not terminate your Internet connection here, as this is central to the integration of a virtual telephone system. If necessary, a Increase in bandwidth Your internet connection make sense.
  • Internet connection: Since VoIP and cloud telephony run over the Internet, an Internet connection with sufficient bandwidth is essential. Since more and more services are being processed over the Internet in the sense of the Next Generation Network (NGN), it is worth investing in a stable and powerful Internet connection. A reliable internet connection is mandatory in corporate telecommunications. To guarantee this, the bandwidth of your Internet connection should be at least 64 kBit / s. It should be noted here that the bandwidth often determines the number of extensions available. So if you have a large company with several employees, it is worth investing in a high-quality Internet connection.
  • IP-capable router: As the name suggests, nothing is more important in IP telephony than an IP-capable router. If you are already using a modern, IP-capable router, this is suitable for all-IP telephony and you don't have to buy a new router. If you do not yet have an IP-enabled router, you have to retrofit it in order to be able to use VoIP or cloud telephony.
  • Take the phone number with you: If you want to take your phone number with you when you switch to virtual forms of telephony, you should apply to have it with you as soon as possible. By your current provider, you can release the phone numbers at the end of the contract in advance while you ask your new provider to port the old phone numbers.
  • Migration to VoIP or cloud telephony: As a company, you have to remain available at all times and be able to rely on your telecommunications infrastructure. So that the Switching from ISDN to VoIP does not lead to a “hard cut” with technical difficulties, you should rely on the new VoIP telephone system. Talk to your IT service provider specifically, he will be able to present solutions for a smooth changeover.

From ISDN telephony to All-IP - this is how you master the transition!

The realignment of ISDN telephony in the sense of All-IP and the switch to VoIP and cloud telephony is inevitable. It is true that sooner or later it makes sense to completely switch communication in companies to Internet telephony, but there are also some devices that can guarantee a step-by-step change. Here there is with SIP trunks and VoIP gateways (also called VoIP adapters) are powerful interim solutions that allow a smooth migration towards All-IP can guarantee. One speaks of a smooth migration when the switch to IP telephony is not carried out in one step, but in stages. When switching from ISDN PBXs to VoIP telephony, for example, the landline connection can continue to be used for the time being. Incoming calls can continue to run over ISDN for a while, while outgoing calls are already being handled using Voice over IP.

Telecommunication solutions such as SIP trunks or VoIP gateways are also a central component of hybrid telephone systems. Hybrid telephone systems are ISDN-based telephone systems that are upgraded for Internet telephony by integrating SIP trunks or VoIP adapters.

There are some useful interim solutions, However, a timely discussion of the All-IP topic is inevitable. Virtual telephone systems are the future of telecommunications, with the use of VoIP or cloud telephony having some useful advantages. As a rule, the provider of your ISDN PBX should have already approached you with a contract change or new offers. If this is not the case, actively inquire about offers of telephone systems with Voice over IP.

SIP trunks enable smooth migration towards All-IP

If you have not yet found the right provider for your All-IP conversion or if you want one, SIP trunks, VoIP gateways or S0 buses offer optimal interim solutions. SIP trunks allow an ISDN telephone system to be connected to the Internet, which enables the use of VoIP and cloud telephony. This works with the help of a SIP trunk, which uses SIP (Session Initiation Protocol) to set up and clear communication connections on the Internet. Put simply: The SIP trunk ensures that calls in ISDN telephone systems can be sent over the Internet in individual data packets.

By integrating SIP trunks, ISDN PBXs are made Internet-enabled, whereby it is possible to conduct several parallel calls via a single Internet connection. The number of possible parallel voice connections depends largely on the bandwidth of the Internet connection and the settings of the telephone system. A larger bandwidth enables the use of several extensions, while a lower bandwidth is associated with a reduced number of extensions. SIP trunks are similar to the system connections in ISDN telephone systems, although they can be described as a modern, IP-based form of primary rate connection. One of the great advantages of using a SIP trunk is that you can continue to use the existing hardware of your ISDN PBX.

Our expert tip: SIP trunks as sustainable elements of telecommunications

“SIP trunks enable an ISDN PBX to be connected to the Internet. This makes them important core elements that ensure a gradual migration towards IP-based telephony. If you decide to switch completely to VoIP or cloud telephony in the future, SIP trunks can also be used in virtual telephone systems. Here they ensure the networking of the VoIP provider with a VoIP-enabled telephone system and thus ensure the transmission of telephone calls over the Internet. Entire blocks of telephone numbers as well as individual telephone numbers or extension numbers can be assigned to a SIP trunk. The advantage here is that only one account is required for all end devices and, if necessary, all end devices can be selected via this account. A SIP trunk also makes it easier to switch to a virtual PBX, which is particularly useful in view of the upcoming shutdown of the ISDN network. It should be taken into account here that after the ISDN is switched off, the service and maintenance offers for telephone systems with ISDN components will decrease drastically. The integration of a SIP trunk is therefore a perfect interim solution for one to virtual telephony, as it can be used without any problems in the event of a complete switch to All-IP. "

VoIP adapters and S0 buses as powerful interim solutions

Similar to SIP trunks, VoIP adapters also offer the option of continuing to use an ISDN telephone system after the ISDN network has been switched off. VoIP gateways are electronic devices that convert voice and data signals from traditional communication into VoIP data packets. Both analog and ISDN signals fall under the concept of classic communication. By integrating VoIP adapters in ISDN systems, the telephone systems are made IP-enabled, which is done by converting the protocol. It works as follows: The VoIP adapter converts signals from the ISDN PBX and converts them into digital data packets, which can then be transmitted over the Internet. This conversion of the data packets enables VoIP gateways to continue using ISDN telephone systems temporarily, even after the ISDN network has been switched off.

In addition to a VoIP adapter, an S0 connection (also known as an S0 bus) allows the continued operation of an ISDN system in the sense of the next generation network. All you need is an IP-capable router with an S0 connection, via which the router then connects your ISDN PBX with the traditional telephone network.

By using the S0 bus, the signals from the ISDN telephone system are made digitally available and combined in a network. Thus, an S0 bus can be a good alternative to using a VoIP gateway. Providers such as Cisco (e.g. Cisco Spa 112), Gigaset (e.g. Gigaset DX800A) or Auerswald (e.g. Auerswald COMpact 3000 ISDN) offer numerous options for temporarily using your old ISDN connection even after ISDN has been switched off continue to use.

VoIP gateway and S0 bus as interim

ISDN PBXs can be used in a variety of ways even after ISDN has been switched off. However, you should be aware that you can only benefit to a limited extent from the advantages of a virtual telephone system. In addition, the use of temporary solutions such as VoIP adapters or S0 buses is problematic because they are difficult to expand. As your company grows, expanding a telephone system with media gateways is complicated. In particular, because when ISDN is switched off, technical support and maintenance options also end or are significantly reduced in many cases. If there are technical problems, it will be difficult to find the right service and the right spare parts for a repair after the ISDN shutdown in 2022. This is why options such as VoIP gateways or S0 buses are more of a temporary solution than a long-term alternative to VoIP PBXs. SIP trunks have a special position here: SIP trunks differ from VoIP adapters and S0 connections in that they can be easily integrated into VoIP telephone systems and can therefore still be used after the switch to All-IP .

Virtual telephone systems ensure efficient telecommunications

While switching off ISDN is seen as an annoyance in many places, the switch to All-IP also offers a unique opportunity. The orientation towards the next generation network ensures that the telecommunications networks are centralized. Where previously different ways of transmitting data streams were used, all data is transmitted over the Internet. The Next Generation Network thus provides a universal infrastructure in which various data streams are bundled and transmitted over the Internet. For virtual telephone systems - such as Voice over IP telephony or cloud telephony - the NGN is indispensable, as it forms the basis for the transmission of voice information in the form of digital data packets.

Cost savings

All-IP ensures internet-based telecommunication. This means that your company's existing internet connection can be used while There are no costs for an ISDN connection. The elimination of license and maintenance costs for ISDN PBXs as well as the low call costs in IP telephony ensure further cost savings.


VoIP PBXs allow unprecedented flexibility. As your business grows, extensions can be added here with one click. In addition, many settings - such as forwarding calls or call barring - can be conveniently set or edited online.

Location independence

IP telephony is location-independent. This means that users of virtual telephone systems are no longer tied to the location of the telephone, but can make calls from virtually anywhere. All you need to do is install the appropriate software on your smartphone, tablet or PC. The location-independence of IP telephony is particularly practical when you have several locations or in the home office.

Increased range of functions

Compared to ISDN PBX systems, virtual telephone systems score with an increased range of functions. In addition to classic functions such as holding, toggling or picking up, VoIP PBXs also offer features such as automatic call forwarding, the ability to make calls with particularly high voice quality, a central telephone book or the networking of several locations. Different solutions for failure safety are also widespread.

All-IP is the technology of the future, whereby telecommunications have already been permanently changed by techniques such as VoIP or cloud technologies. Digital innovations are practically the order of the day, which means that the concept of All-IP and the technology behind it are constantly being improved and supplemented. As a company, you have a duty to always be an accessible and reliable contact person for your customers. Especially with regard to the future and the shutdown of ISDN, only virtual telephone systems can guarantee the level of accessibility and reliability that service-oriented companies should present. For this reason, IP-based telephone systems are the only sustainable form of telephony.

Are you still unsure which telephone system is best for you? Fill out our form and let us advise you - free, secure and transparent.

Did you know? Effects of the switch to All-IP on alarm systems

At first glance, the switch to All-IP and alarm systems have relatively little to do with each other. However, when ISDN is switched off, the transmission path of your alarm system should be checked, as some alarm systems still forward signals to the emergency call center using ISDN or analog telephone networks. If the ISDN connection is now switched to Voice over IP in the sense of All-IP, there will be problems with the alarm forwarding, as this no longer works. As a result, the emergency call literally comes to nothing, which can have fatal consequences. If the alarm signal is still being transmitted via ISDN or analog telephone networks, the interface must be converted or renewed. The best thing to do here is to contact the provider of your alarm system, who should be familiar with the necessary technical innovations. Problems with the changeover to All-IP only affect alarm systems that use the ISDN network for alarming purposes. Many devices are already IP-capable here. However, it may be necessary to purchase new hardware under certain circumstances. If fire alarm systems are used in your company, the transmission routes of these should also be checked, since, depending on the model, BMAs are also connected to emergency call centers via ISDN.