Alpha Galileo – A consortium of universities, research institutes, equipment vendors and one telecom operator joined forces in the ‘Scalable advanced ring-based passive dense access network architecture’ Sardana project to develop pioneering techniques to dramatically improve the scalability and robustness of the fibre-to-home networks that already serve millions of European internet users. Supported by EUR 2.6 million in research funding from the European Commission, the project not only demonstrated connection speeds of up to 10 Gigabits per second (Gbps), around 2,000 times faster than most Internet users experience today, but the researchers showed that such speeds can be achieved at relatively little extra cost using existing fibre infrastructure and off-the-shelf components.
The approach uses existing infrastructure or involves changing components that can be cheaply upgraded to achieve 10 Gbps performance.
Though still in the experimental stages, the fully optical technology, if deployed commercially, would mark a giant leap forward in fibre network performance, directly addressing one of the biggest challenges currently facing service providers and consumers.
SARDANA researchers are proposing a new access network architecture using fibre to the home that provides new functionalities and extended performance.
Although SARDANA is at least 24 months from commercial rollout (as of Jan 2011), Tellabs and others are already talking about the applications it can enable or dramatically improve. HDTV, UHDV and 3D TV are some potential consumer beneficiaries, along with holographic telepresence and telemedicine in the business market.
The largest, most immediate market opportunity is mobile backhaul, which is struggling to keep up with about 130,000 TB of traffic per month, according to iGR, a research firm. By 2014, the monthly load will hit 990,000 TB.
SARDANA’s compatibility with existing GPON technology is one of its benefits. Others include:
• Fewer COs, reducing OpEx.
• 100 km (62 mile) signal range, more than triple the reach of today’s PONs.
• 32 times more bandwidth on a single-mode fiber than today’s best PONs provide. SARDANA uses WDM to drive up to 32 10 Gbps wavelengths down a fiber where only one currently goes.
This breakthrough delivers 128 times the bandwidth of G.984 GPON and will enable operators offer premium-priced, high-bandwidth packages to large commercial customers. For smaller businesses and residential customers, SARDANA provides higher split ratios: up to 1,024 subscribers per PON.
• Cheaper, simpler installations. Today’s optical network connections rely on a pair of laser transmitters for one specific frequency of light to and from the end-user’s location. SARDANA replaces these transmitters, which can cost as much as $1,000 each, with smaller, colorless ONTs.
Because they have no laser and need no tuning, these passive ONTs are much less expensive and can manage all 32 incoming wavelengths. That slashes inventory requirements.
• Greater network resiliency, thanks to a dual-ring architecture. This also gives PONs greater stability comparable to Ethernet and legacy SONET platforms.
• More bandwidth and network intelligence for smart mobile backhaul applications. Only optical networks can keep up with skyrocketing mobile data traffic
Conventional fibre-to-home networks, also known as Passive Optical Networks (PONs), have a tree-like structure with the telephone exchange central office at their root. ‘Passive’ refers to their use of optical splitters which do not require additional power. From there a thick main trunk of cables spreads out into smaller branches to homes and businesses. Conventional tree PONs use Time Division Multiplexing (TDM), a multiplexing method inwhich signals are transferred apparently simultaneously as sub-channelsin one communication channel, but are actually physically taking turns on the channel. In practice, this means that a 5 Gbps connection at the central office can turn into a 30 Mbps downstream connection by the timeit reaches someone’s home, with upstream bandwidth usually a mere fraction of that.
From trees to rings
The Sardana researchers are proposing a different and totally new approach, enabling not only much faster connections, but more capacity and robustness. Instead of a single big tree, they are proposing multiple smaller trees branching out to end users from a main ring. The ring transmits signals bidirectionally from the central office using Wave Division Multiplexing(WDM), a multiplexing technology that enables different signals to be carried simultaneously on the same optical fibre by using different wavelengths of laser light. At Remote Nodes along the ring, the signals split off onto single fibre trees to homes and businesses using TDM technology.
The 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 results in massive increases in connection speed.
‘Using WDM on the ring means we can multiply bandwidth by 40 wavelengths so individual users can enjoy 1 Gbps: not just in one direction, but in both directions, both upstream and downstream,’ Prof. Prat says. ‘This could open the door to entirely new applications that are simply not possible today, such as high definition video conferencing.’
Laboratory tests by Finnish equipment vendor Tellabs were followed by a field trial near France Telecom-Orange’s facilities in Brittany, France,and a demonstration at the Fibre to the Home Council (FTTH) in Milan. Using emulation technology combined with real-world infrastructure, 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 300 Mbps. Separately, the researchers also demonstrated that the technology could be used to transmit optical signals up to 100 kilometres from the central office in order to provide up to 250 homes with asymmetrical 10 Gbps downstream and 2.5 Gbps upstream connections. Crucially, from a commercial point of view, such improvements can be achieved at little extra cost and the technology maintains network transparency, supporting the use of the same infrastructure by multiple service providers.
n the trials, the Sardana team employed ONU chips developed by Alcatel-Thales, which do not require additional wavelengths to carry out the conversion and return an upstream signal – ensuring the entire network remains fully optical. Similarly, the Remote Node connections between the WDM ring and the TDM trees are also fully optical, drawing additional power from pump lasers at the central office.
‘The architecture is completely passive – it can be buried entirely underground and doesn’t require any maintenance,’ Prof. Prat emphasises.’Much of the infrastructure is already there: rings exist in metropolitan areas and trees are widely used, though they currently workwith very different transmission technology. Our approach turns this infrastructure into a fully optical passive solution.’
The project partners are continuing to develop the technology, which has already elicited interest from operators in Europe, the United States and China.