EU Researchers Propose Cheap Fibre Rings For 10Gbps FTTH

Tom Jowitt is a leading British tech freelance and long standing contributor to TechWeek Europe

The EU Sardana project proposes a cheap route10Gbps broadband – if you have fibre

Researchers backed by the European Commission have said that premises in rural area could have cheap 10 Gbps access, if operators switch their ibre-to-the-home (FTTH) networks to a structure based on rings.

The dramatic claim comes from a consortium of universities, research institutes, equipment vendors and a single telecom operator, who have banded together under the ‘scalable advanced ring-based passive dense access network architecture’ or Sardana project, backed by European Commission funding to the tune of 2.6 euros (£2.1m).

Network Architecture

Essentially the Sardana project is seeking to develop new ways and techniques to dramatically improve the scalability and robustness of fibre-to-home networks in all locations, including rural areas (providing of course they have a fibre network connection).

The research group claims to have demonstrated connection speeds of up to 10Gbps (Gigabits per second), and boasted that such speeds could be achieved at relatively little extra cost using existing fibre infrastructure and off-the-shelf components.

The group is using an experimental fully optical network architecture. If the technology was deployed commercially, it would mark a giant leap forward in fibre network performance, and could satisfy the ever increasing demand for more bandwidth, the group says.

This is quite a claim, but the Sardana researchers genuinely believe they have found a viable alternative to European network operators having to invest billions in upgrading their network infrastructure.

“We are proposing a new access network architecture using fibre to the home that provides new functionalities and extended performance,” Professor Josep Prat was quoted as saying. Prat is a researcher in the Optical Communications Group (GCO) at the Universitat Politècnica de Catalunya (UPC) in Spain and the scientific coordinator of the Sardana project.

Tree Structure

At the moment, conventional fibre-to-the-home networks, also known as Passive Optical Networks (PONs), have a tree-like structure with the telephone exchange acting as the central point. This model means that from the telephone exchange, cables spread out into smaller branches to homes and businesses.

Now conventional tree PONs use Time Division Multiplexing (TDM). This is a multiplexing method where signals are transferred apparently simultaneously as sub-channels in one communication channel, but are actually physically taking turns on the channel.

What this means in the real world is that while a central location could enjoy a 5Gbps connection, by the time it branches out and reaches a house or building, it can be a 30Mbps downstream connection.

Multiple Trees

The Sardana researchers are proposing a different and totally new approach.

Instead of the usual single big tree, they propose multiple smaller trees branching out to end users from a main ring. The ring transmits signals bidirectionally from the central location using Wave Division Multiplexing(WDM).

WDM differs from TDM is that it enables different signals to be carried simultaneously on the same optical fibre by using different wavelengths of laser light.

This bidirectional ring approach improves network robustness because if the cable is broken at any location on the WDM ring the signal will still reach end users from the other direction. It also apparently results in huge increases in connection speed.

“Using WDM on the ring means we can multiply bandwidth by 40 wavelengths so individual users can enjoy 1Gbps: not just in one direction, but in both directions, both upstream and downstream,” said Professor Prat. “This could open the door to entirely new applications that are simply not possible today, such as high definition video conferencing.”

Cheap Upgrade

What makes this research credible is the laboratory tests by Finnish equipment vendor Tellabs, coupled with a field trial near France Telecom-Orange’s facilities in Brittany, France. A  demonstration was also conducted at the Fibre to the Home Council (FTTH) in Milan.

The tests showed that the network is able to serve between 1,000 and 4,000 users within 20 kilometres of the main ring, with symmetric internet connections at speeds of around 300Mbps. Separately, the researchers also demonstrated that the technology could be used to transmit optical signals up to 100 kilometres from the central location in order to provide up to 250 homes with asymmetrical 10Gbps downstream and 2.5Gbps upstream connections.

And crucially the researchers say that such improvements can be achieved at little extra cost.

“Our approach uses existing infrastructure or involves changing components that can be cheaply upgraded,” said Prof. Prat. “The architecture is completely passive – it can be buried entirely underground and doesn’t require any maintenance. Much of the infrastructure is already there: rings exist in metropolitan areas and trees are widely used, though they currently work with very different transmission technology.”

The project partners are continuing to experiment with the technology, but it has already elicited interest from operators in Europe, the United States and China.

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