Migration to Next Generation Networks

The Public Switched Telephony Network (PSTN), is the oldest and most widely used network in the world for the provision of legacy telecommunications services and it has been evolving ever since Alexander Graham Bell made the first voice transmission over wire in 1876. The ongoing digital evolution is transforming and disrupting the world of telecommunications and the demand for new services and increased capacity has rendered existing telecommunications technologies as obsolete in the shift to a ubiquitous IP world. The migration to IP-based networks is fundamentally changing how services are delivered and how they are consumed. The ECC is has been following developments in this area over the last 10 years. More recently, network operators in Europe have started the migration process and the ECC has therefore identified network migration as a key challenge in its strategic plan for the period 2015-2020.  


The PSTN was initially designed to provide a short distance connection between any two points or end-users (point-to-point) on a network. Over time the telephony network evolved to support more end-users and endpoints through a network of switches designed to facilitate ubiquitous network connectivity that enabled voice communication over long distances. By placing switching equipment in centralised locations, network engineers were able to interconnect networks and thereby connecting a large numbers of end-users via these switches to maximise network access. Thus, the concept of the circuit-switched network was born. For many decades the access network and the core network of the PSTN was analogue, which resulted in long distance calls with poor audio quality (i.e. calls with a low signal level and a high noise level). In order to implement much-needed improvements, network operators started to convert the core network from analogue to digital based on PCM-technology.

In the 1980s the telecommunications industry began to deploy network technology capable of supporting digital services. The industry made network deployment decisions based on the assumption that digital services would follow much the same pattern as voice services, and they conceived a vision of end-to-end circuit-switched services over a network which became known as the Integrated Services Digital Network (ISDN). The focus on ISDN was on transmission of voice signals and low–speed data signals. The PSTN was originally designed to offer fixed telephony services only. The increasing demand for Internet access in the 1990s and the requirement for greater bandwidth to provide IP-based services required a shift in focus. This, coupled with a prolific demand for mobile telephony services demonstrated the need for a network capable of supporting all these services simultaneously.

The shift to IP - Demand for additional services, higher speeds and better quality

The need for greater capacity and support for multiple services resulted in a shift towards IP-based networks. Circuit-switched networks (PSTN/ISDN) began to be migrated to a new architecture called Next Generation Networks (NGN) based on an all-IP platform (IP multimedia sub-system (IMS) with softswitches). The ongoing migration to NGN is a process in which whole or parts of the existing networks are replaced or upgraded to the corresponding NGN components providing additional services on a network capable of higher speeds and quality of service while attempting to maintain legacy services provided by the original network.

Drivers for migration – Operator perspective

Existing PSTN/ISDN voice networks are slowly reaching end of life. Apart from a reduction in demand for PSTN/ISDN services other factors are also leading operators to re-evaluate their network strategies. These include:

  • The exhaustion of stocks of spare parts;
  • A reduction or cessation of support for network equipment and software by the major vendors
  • A dearth of expertise and experience in maintaining these networks caused by the retirement of engineers with the requisite skills and experience to support legacy systems
  • Fewer customers has led to lower revenues which has simultaneously resulted in a higher maintenance cost per customer.
  • End-users want to have a wider choice of communications applications to choose from including e-mail, IM, video chat and social media. Therefore, from the operator’s perspective, the motivation for migration is to lower costs and exploit revenue generating opportunities.
  • NGN equipment is cheaper to purchase and to operate a common platform for multiple service offerings which are all IP-based.

While the operator’s core concerns are to reduce costs, increase revenue and remain competitive they must also take account of their regulatory obligations in their respective migration strategies such as maintaining access to emergency services, supporting number portability and ensuring a high QoE/QoS for users. 

In order to address this strategic challenge and provide guidance to European regulators, the ECC’s Working Group Numbering and Networks (WG NaN). through its Project Team on Technical Regulatory Issues (PT TRIS) prepared ECC Report 265 which examines the regulatory aspects of migration. The Report is essentially based on an exchange of experiences in the regulation of migration toward IP-based networks and services between different CEPT member states through their respective national administrations. The report is also informed by presentations made to PT TRIS by various operators throughout Europe who have already commenced or completed their migration projects.

ECC Report 265 does not aim to mandate specific regulatory measures or harmonised approaches but may be used to inform future policies with the objective of providing a better understanding of the technical and regulatory challenges of migration and some guidance on how this evolution will pave the way for the provision of multiple services on a fast and reliable IP platform.

ECC Report 265 on Migration from PSTN/ISDN to IP-based Networks was adopted at the 16th meeting of WG NaN in Helsinki on 31 May 2017.

For further information on the subject of migration to all-IP networks, please see the September 2017 edition of the ECC Newsletter which contains an article on migration.

Updated: 19 September 2017, 16:20