Cloud Telephony or ISDN Replacement: What Fits?

ISDN is history in Germany: the major network operators have switched classic ISDN technology nationwide to IP-based telephony ("All-IP"). Anyone still running a business on old ISDN lines, or taking over an existing phone system, isn't facing the question of "whether" anymore, but of how to make a clean switch - and what's easy to overlook along the way.

What's changed technically

All-IP means all communication - telephony included - runs over the internet protocol instead of dedicated, separate phone lines. For end users, plain calling often changes little: numbers stay portable, and extensions and hunt groups keep working. What matters, though, is that the underlying technology places entirely different requirements on network, end devices, and connected auxiliary systems than a classic ISDN setup did.

The underestimated auxiliary systems

The real effort in ISDN replacement rarely lies in the main phone line, but in devices that quietly ran alongside the old phone system:

• Fax machines connected via analog ports on the phone system, which stop working without adjustment.
• Alarm and fire detection systems that automatically report faults to a control center over a phone line.
• Elevator emergency call systems, which are legally required to maintain a working voice connection to an emergency center.
• Older card payment terminals with their own phone connection.
• Door intercom systems wired through the phone system.

Each of these systems needs either an IP-capable adapter, a manufacturer software update, or in some cases a device replacement. If this gets overlooked during migration, it usually only becomes apparent when the system fails to work in an actual emergency.

Planning the migration cleanly

Before the actual switch, it's worth doing a complete inventory of every device currently connected to the phone system - not just the obvious phones. For each device, it should be clarified whether the manufacturer offers an IP-capable alternative, whether an adapter is sufficient, or whether a replacement is needed. Only then can the migration be planned so that no auxiliary system fails unnoticed.

Why the switch pairs well with a cloud phone system

Anyone who has to migrate anyway usually checks in practice whether a cloud phone system makes more sense than a plain one-to-one replacement of the existing technology. The effort for planning and migrating the auxiliary systems is similar either way - moving to a cloud solution then additionally brings more flexibility for extensions, call forwarding, and location-independent work, without requiring a second migration step later.

Checklist

• Have you compiled a complete list of every device connected to the phone system (not just phones)?
• Have you checked IP-capable alternatives for fax, alarm system, elevator emergency call, card terminal, and door intercom?
• Have legal requirements (e.g. elevator emergency call) been accounted for in the new system?
• Has number portability and hunt group setup been planned for the switch?
• Have you checked whether the switch can be combined directly with a cloud phone system?

Conclusion

The real work in ISDN replacement is rarely the main line - it's the forgotten auxiliary systems. With our Cloud Phone System we handle the planning and execution of your switch, including an inventory of every connected device. Get in touch via our contact page if you're unsure which of your systems still depend on ISDN.