Most service providers recognize that fibre architectures are the end-game to effectively deliver IPTV to mass markets. However, mass deployment of fibre requires a significant investment – both in terms of time and money. Hence, for many service providers, DSL (when available) remains the most cost-effective and expedient way to deploy IPTV and other high-speed broadband services – through maximum re-use of the existing copper infrastructure, in combination with a gradual migration to fibre. Especially in challenging economic times, this is a valid business proposition.

Due to the physical nature of copper, however, delivering IPTV over digital subscriber lines (DSL) presents a number of obstacles – including line stability and quality of service issues, which might result in artifacts and service interruptions if not properly addressed.

Fortunately, continuous innovations allow service providers to significantly increase the capability of their copper networks to deal with very high-speed data and IPTV quality of service requirements.

BT’s Broadband Accelerator

BT’s Broadband Accelerator, otherwise known as the iPlate, is a nice, practical example of how noise can be reduced to improve the end-user’s service experience. However, while BT claims that the Broadband Accelerator may boost speeds by up to 1.5Mbps on its lines, unfortunately it cannot be leveraged anywhere else in the world – as it solves an issue that is unique to the BT network.

UK phone sockets have a unique configuration, including a third wire which was historically used by pulse dialling telephones. Even though this third wire is no longer used by touch tone telephones that are in common use today, it does pick up and emit electro-magnetic pulses – generating noise and leading to lower bitrates. Basically, BT’s Broadband Accelerator addresses this issue by using a metal plate that isolates the third wire in the socket. A clean and simple solution – but only for a single, very specific source of noise. Unfortunately, there are other sources of noise that can impact DSL performance, cross-talk from neighbouring lines being a key example. Ultimately, the Broadband Accelerator does not solve the crosstalk issue at large.

Smart DSL: an alternative approach

Increasing the signal-to-noise ratio (i.e. using a higher noise margin) is the traditional approach to stabilising lines that are impacted by crosstalk – but this results in a loss of bitrate, something that is not well suited in today’s triple-play world.

Smart DSL, an alternative technology developed by Alcatel-Lucent, targets operators deploying higher-speed services over asymmetric DSL (ADSL) and very high-speed DSL (VDSL) lines.

Basically, Smart DSL uses Artificial Noise (on ADSL) or Virtual Noise (on VDSL) to mask noise and results in increased bandwidths for high bitrate service delivery. Its ultimate goal is to ensure that the copper network can deliver the quality of service and quality of experience promised to (and expected by) end-users.

Smart DSL seeks to achieve optimal line stability with minimal bandwidth loss, allowing operators to expand coverage of their copper networks for the deployment of IPTV and other premium bitrate services.

The technology has also demonstrated improvements in another issue that is typical of copper networks: energy consumption, claiming to enable a significant reduction (-25 per cent) of the modems’ power consumption across a service provider’s subscriber base without causing any line stability issues.

Nightmare or opportunity?

All in all, thanks to a number of recent innovations, DSL networks are perfectly capable to support end-users’ need for high-speed broadband services, for a number of years to come.

In Belgium for instance, the “Broadway Project” of incumbent operator Belgacom builds on a state-of-the-art, fibre-to-the-node (FTTN) VDSL2 access architecture that fully leverages Belgacom’s existing assets. The service provider has thus been able to cover (in less than 2 years time) more than 60 per cent of Belgian households with a sustained, video-grade throughput of 20Mbps, providing its customers with a full array of triple play services – including multiple IPTV streams, faster internet connectivity and HDTV.

Stefaan Vanhastel is DSL product marketing manager at Alcatel-Lucent