Change of Times: Data over Voice to Voice over Data

Recently, I reflected a bit over how fixed and mobile networks have evolved in the past 30 years, i.e. since the mid-1980s. For the first time I realized then that during that time frame, networks have been totally turned inside out.

Here’s what I mean:

In the 1980’s people had a telephone line at home and the only service running over it was voice. The network and the service were the same. Voice calling was a circuit switched service which means that a physical end to end connection was established between two parties by using switching matrices in switching centers to transparently connect two parties during a call

In the 1990’s the same circuit switched technique was still used for voice services. Digitized in the back end, yes, but still circuit switched. However, by that time, data modems had become very popular to connect to Bulletin Board Systems (BBS) or to an Internet service provider. Data to and from the other end was exchanged over modulated tones over the speech channel. In other words, voice and data services used the same underlying network.

In the 2000s, DSL became popular and for the first time, voice and data services were not using the same underlying network infrastructure anymore. While voice telephony continued to use a circuit switched network, Internet connectivity over DSL was using a packet switched form of transmission on the copper cable to the customer in a different frequency band from the voice channel. This was the decade of separation.

And now in the 2010s it is becoming more and more common that the so far circuit switched voice service is transitioned to a voice over IP service, e.g. fixed line IMS. This means that the copper cable to the subscriber is now just used by DSL and the frequency band so far used for the voice service has now also been taken over by DSL.

Let’s think about this for a moment: Back then the voice channel was used to transmit IP packets. Today, IP packets are used to transport a voice channel. A total reversal of roles in telecommunication with a step of total separation in between to two.

In the mobile world pretty much the same thing has happened as well: At first there was only telephony (GSM), followed by voice + circuit switched data (GSM + HSCSD). After that came the split into circuit and packet radio channels with GSM+GPRS and UMTS that had a circuit switched and packet switched radio component. And today there is LTE with Voice over LTE (VoLTE).