In May 2025, the process of closing the 661 remaining active exchanges began, with no possibility of extending these services, putting a definitive end to the service and saying goodbye to the copper voice and data technology that has been with us for the last 101 years.
Practically 94% of ADSL lines have been migrated to fibre optic technology (FTTH), and the remaining 6% to other technologies such as radio access (via the 3G/4G/5G mobile network) or satellite access. Most voice-only lines have been migrated to radio technology.
What has been the history of ADSL?
Although this article deals with ADSL connections, I think it is worth mentioning their predecessors, which also played an important role in the expansion of internet use in our country from the mid-1990s to the present day:
PSTN connections
These connections were colloquially known as ‘56 kbps modems’. Their maximum technical speed was indeed 56 kbps, which usually remained at around 48 kbps. These connections ran over the Switched Telephone Network, blocking the basic telephone service, i.e. you either had internet or you had a telephone.
However, few people may remember this, but Telefónica developed a system to solve this problem. You had to download software onto your PC and if you were connected to the internet and someone called your landline, the software offered you two options:
- Answer the call from your PC using the installed software (using VoIP)
- Answer the call from your landline. To do this, the system notified the caller with a message asking them not to hang up, and in the meantime, the software disconnected the modem to switch the telephone line from data to voice. It was quite ingenious for the time.
It was the most popular connection until ADSL came along. At first, it was marketed at a price per minute, until flat rates appeared.
ISDN
This service consisted of digital access channels, each offering 64 kbps of bandwidth that could be used for voice and data simultaneously through multiplexing.
Although it was also offered to individuals, this service was most successful in the business segment due to its high cost at the time.
And now we come to ADSL. In the 1990s, Telefónica was immersed in studying other technologies that could provide more capacity to PSTN or ISDN connections. Among these, they considered HFC through their Plan Fotón (a network proposed in the 1990s for TV services), but it was finally discarded after the emergence of ADSL.
Unlike other technologies that competed at the time, such as HFC (now considered legacy compared to others such as FTTH), ADSL was a point-to-point connection. In other words, the cable was private from the exchange to your home and was not ‘shared’ with other users, ensuring bandwidth in the subscriber loop.
What technical modalities did we have?
ADSL, although it has always been seen as a single technology, has had several versions, which we will detail below:
ADSL (G.DMT)
This was the longest-lived standard and the one with which the service began to be marketed. Initially, three options were offered for domestic connections: 256 kbps, 512 kbps and 2 Mbps, although this technology had a theoretical maximum of 8 Mbps. The initial installations were carried out by replacing the PTR (Network Termination Point, which separated the external telephone network from the telephone network in our home) with a splitter. The splitter created two telephone subnetworks in the home, one to which the ADSL router would be connected and the other to which all landline telephones would be connected. This allowed us to have an internet connection and a landline at the same time, unlike with PSTN connections. This installation was carried out with a static public IP address.
Later, to reduce costs, USB ADSL kits were marketed.
These modems were self-installable and single-user (unlike ADSL routers, which were multi-user and required a technician for installation), and instead of the splitter (which also had to be installed by a technician), a microfilter was placed on each landline telephone. The public IP was dynamic in this case
ADSL 2+ (G.992.5)
With the emergence of Imagenio (now Movistar Plus+) and connected devices, the network had to be upgraded. With this technology, speeds of up to 20 Mbps could be achieved, although 3, 6 and 10 megabytes were commercially available. With this technology, ADSL kits are no longer sold, and ADSL modems with WiFi, dynamic IP and microfilters for telephones are now installed, leaving the splitter and static public IP as optional extras with an associated cost.
VDSL (G.993.1)
This modality appeared in the last years of the ADSL boom prior to the emergence of FTTH and was not available for all exchanges. It was a technology that was more sensitive to electromagnetic interference and therefore also required a shorter distance to the exchange. This is where Muxfin exchanges came in (exchanges connected to the backbone network via fibre, with the section from the exchange to the home being copper). Not all Muxfin exchanges were adapted to offer VDSL. The advantages were a faster connection to the network, higher speed and much lower latency compared to ADSL. For this installation, a VDSL-compatible router was required (the ADSL router was not suitable), and due to sensitivity, it was always installed with a splitter. Although the technology allowed a maximum speed of 55 Mbps, it was only marketed at 10 Mbps and 30 Mbps.
And what about the present and future?
For the time being, the outlook is to continue evolving the current FTTH (GPON) to other versions with greater capacity, such as XGPON or XGSPON, which offer greater network capabilities and higher speeds. There is also a greater focus on mobile network uses such as 5G+ and upcoming developments such as 6G, which are already in the pipeline.
