toipWe live in a digital world. Entertainment, work, information, social relations… today everything is digital. The benefits are obvious. Digital information is much easier to store, transfer and handle than analog and is more powerful.  If we think about it we can find many fields where digitalization has had a remarkable impact. In this article, however, we will only consider the impact on telephone networks.

Regardless of whether the telephone was invented by Alexander Graham Bell or Antonio Meucci (or…), it is clear that it started out as analog, and it remained so for many years. Logically, improvements were made over the years but being inherently analog in operation until the mid-60s, deficiencies in the quality of transmitted voice were inevitable. This was especially the case over long distances that required signal regeneration at intermediate stages, leading to information loss and the introduction of noise. The digitalization of the telephone network was a breakthrough in this regard, since the digital signal is transmitted unchanged regardless of the distance and of the intermediate stages required between sender and receiver.

Integrated Services Digital Network (ISDN)

While the move to a digital network paved the way for its use with a range of other services in addition to voice, the final leg, the last mile, also needed to be digital. This step took place many years later with Integrated Services Digital Network, ISDN. As the name suggests, ISDN allows different services to be used over the telephone network on a single line, digital of course.

The advantages of ISDN are clear: firstly, the sound quality (which is why even today they are still widely used by the radio industry), secondly, the extra features (rapid call setup, support for multiple terminals on the same line or direct inward dialing and caller ID), and thirdly, the additional services such as data or video transmission.

ISDN was introduced by CCITT (ITU-T) in 1988 and had its golden moment during the 90s, being deployed with varying success in countries around the world such as Japan, Australia, India and the United States. The biggest impact was in Europe, however, in countries like Norway, Denmark, Switzerland and above all Germany, which had 25 million channels (29% penetration) and one in five lines installed worldwide.

In the late 90s and early twenty-first century two events mark the decline of ISDN; on the one hand, ISDN cannot keep up with market demands for greater speed, and on the other, the cost of Digital Signal Processors (DSP), which allow more advanced line modulations, lowers significantly. It is the beginning of ADSL and the decline of ISDN.

ISDN, the new paradigm in communications

During the first decade of the twenty-first century, ISDN gradually loses ground to ADSL and from 2010 all ISDN service carriers gradually announce its withdrawal. In 2010, for example, NTT announces its intention to migrate all ISDN phone lines in Japan to IP technologies, in 2013 Verizon decides not to install anymore ISDN lines in the USA and in 2015 BT announces its intention to discontinue the network in the UK. Curiously, however, Deutsche Telekom (DT) in Germany adopts the most aggressive stance. By far the world’s largest ISDN provider, it has already begun migration to ADSL/IP technologies having set an aggressive horizon of 2018 for cutting off ISDN completely.

All carriers with active ISDN networks will no doubt be following the transition of the German DT network very closely and it will likely mark the way forward. DT’s commitment is to network modernization and improving customer service while minimizing the impact on the customer. The proposal, therefore, is to offer data services and voice over IP on the same telephone line (ADSL/VDSL) but at the same time giving the customer the opportunity to keep their existing ISDN infrastructure, emulating the ISDN lines from the EDC to their current ISDN PBX.

The use of xDSL and IP services allowing the customer to maintain their internal ISDN infrastructure practically eliminates any impact on the customer, who controls the evolution of the network to an integrated and up-to-date service.

This is an ambitious project and key for Deutsche Telekom. For this reason, following a rigorous selection process, the company has forged close relationships with partners who have proven ability in providing the solvency, experience and agility needed. Within this framework, Teldat has been entrusted by Deutsche Telekom with the task of supplying the access devices.

Marcel Gil: SD-WAN Business Line Manager