Oliver Nuhn
21. November 2019 0

The marriage of telephone networks

As is often the case at work, I want to get started on something but two other jobs get in the way and by the time I’ve drunk my first cup of coffee, I’ve already lost track of my diary and upcoming commitments. And so it comes to be that while on the phone I remember – well, Outlook reminds me, if I’m honest – that I have a meeting in half an hour’s time. It’s not in the same building, but on the other side of town. I need to head to the car – and fast.

Trapped by a landline

But I’m attached to the good old office landline. The fact I really should have ended the conversation 15 minutes ago is irrelevant at this point. What should I do? Suddenly, every minute counts. For obvious reasons I don’t want to just cut off the person on the other end of the line – my boss or a potential customer, for example.

It’s quite absurd that in 2019 calls from landlines and calls from mobiles still take place in two different universes that couldn’t be further apart. As far as users are concerned, it’s the same functionality – yet behind the scenes lurk different protocols, architectures and so on. Landlines are still always based on a PSTN (public switched telephone network). Mobile networks, meanwhile, are based on UMTS/LTE (universal mobile telecommunication system / long term evolution). These two parallel universes appear to be locked in a sort of trench warfare, wanting nothing to do with each other, let alone a connection.

The dream of digitalization

And we’re always going on about digitalization! In the real world of digitalization, my current call would be merely a service and it would be completely independent of the end device being used. This would give me the option to simply transfer my call from the landline to, say, my cellphone and vice versa without the person on the other end noticing.  I would be able to stay on the phone without needing to hang up and still be free to quickly dash to the car and make it to my next meeting on time.

Notice all the “woulds” in there? Well, they should really be “wills”. Admittedly, conventional telecommunications systems are still miles away from fulfilling this dream. State-of-the-art unified collaboration systems can achieve it, albeit with a complex solution using a soft client or app on the relevant smart devices – and only if those have actually been installed and are being used. All the same, in today’s All-IP world, flitting between different devices is no longer an impossibility. This is down to the IP multimedia subsystem, known as the IMS layer for short, which uses IP as the communication standard and SIP (session initiation protocol) as the protocol. Until now, IMS has been predominantly used for mobile communication to connect “conventional” mobile networks such as GSM or UMTS with IP-based networks.  However, it also ensures providers can easily integrate those illustrious add-on services. For example, these can help you check whether it’s worthwhile picking up the phone in the first place by telling you whether the person you’re trying to reach is able to take your call (as long as they’re using the same add-on).

IMS makes connections possible

IMS is composed of three ‘layers’. The first is the connectivity layer, which connects different devices together and is where routers and switches are located, too. Secondly, there is the control layer, which manages the different sessions and is where users and their devices are authenticated. Last but not least, you have the service layer, where different services, in principal servers for content and applications, are implemented and connected.

From the 3GPP standardization committee’s point of view, IMS is a prime example of how a communication infrastructure should be and is now implemented in just about every All-IP network. Interestingly, a lot of providers recognize this standard, which in turn means that solutions such as IP Centrex can be connected to a mobile network via SIP trunking. It also means I can now deal with two people at once – my current caller and the person waiting for me on the other side of Frankfurt. It will only start to get tricky if I still haven’t finished my call by the time I reach my destination. Then I’ll need a Nuhn bot that can take over the call for me. But that’s another story…

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