London, April 2005

Fibre to the Home: Thoughts from Japan

The bourgeoning Fibre to the Home market in Japan could be the model for future developments in Europe

Typical FTTH deployment over a PON network

Japan is leading the way with fibre to the home where 50% of new fibre deployed is used for FTTH and a customer base of 2 million subscribers grows at 90,000 per month. Tough competition fuels this market. When customers sign for FTTH services, it’s difficult for competitors to regain the customer so the race is on for the initial signatures. Japanese incumbent provider (NTT) faces competition from USEN, Yahoo BB and KDDI as well as the utility companies Tokyo electric and Kansai electric (K-OPT). So the motivation to deploy infrastructure exists whilst peer-to-peer file sharing, on-line gaming and voice over IP fuels demand.

The European situation could go the same way. The national incumbent providers currently face less imminent competition allowing longer-term viewpoints, but there are many cities across Europe with insufficient broadband deployment that need to address business requirements for the local economy. So competition could grow from utility companies keen to capitalise on these opportunities, which in turn could pressurise the incumbents.

Competing technologies

FTTH is not the only broadband solution. Alcoa Fujikura in the USA combine Power Line Communications (PLC) with PON networks, but RF emissions could prevent wide scale European deployment. XDSL cannot deliver high-speed services far from local exchanges and bandwidth limitations clearly limit its longer term potential. Wireless suffers from planning restrictions, latency and licensing problems, limiting its use to rural areas. Every broadband solution has problem, but FTTH ticks every box and offers better bandwidth than any of the alternatives. It’s the only future-proof option.

PON or Point to point

Passive Optical Networks (PON) provides multiple user connections from a single shared fibre, split using passive components. Point-to-point systems use separate fibres for each connection. Figure 1 shows a typical FTTH deployment over a PON Network.
Point-to-point systems are well established in Europe, but in Japan there’s a 50:50 share between PON and point-to-point. Fujikura has supplied 30,000 connections using their FNP EPON systems, and 30,000 point to point connections with their FNT 24 port Media converters.
The choice of PON or Point-to-point is partly influenced by historical familiarity with existing technology (the media converter solution is very well known in Europe), but Japans experience shows that deployment and maintenance costs can be reduced with PON networks. It’s not just deployment costs that are saved; PON allows lower maintenance costs, and takes up less central office space allowing fewer exchanges to cover a wider area.

Connecting and splitting

Japan minimise PON deployment costs by using mechanical splices and field installable connectors. Fujikura’s FMS-025 mechanical splice offers typical insertion losses of 0.1dB and is utilised at the final customer drop where cost savings are greatest and system performance is not compromised.

Passive splitters are a key feature of passive optical networks and two technologies exist; fused couplers and Planer Lightwave circuits, (PLC) Figure 2. At low split ratio’s (1X2, 1X4) Fujikura recommend fused couplers providing low insertion loss at low cost. At higher ratios it’s possible to concatenate fused couplers, but you have to account for component tolerances and additional splices, so when you are operating at distances close to the limit of the PON loss budget the transmission distance is unnecessarily compromised. PLC splitters eliminate this uncertainty. It is a myth that PLC technology is unreliable. Early manufacturing methods used inappropriate curing techniques allowing susceptibility to humidity, but this problem has been greatly reduced and PLC splitters are now widely deployed in Japan. The size of these splitters has also been reduced to 4X4X40mm, (the same as mechanical splices) so they are easily accommodated into splitter trays.

Fault identification

It is essential to carry out fault identification quickly in any network to minimise service costs. The diagnostics solution for PON networks isn’t as problematic as perceived. Fujikura has a completely automated diagnostics system for PON networks widely deployed in Asia. In fact, this system takes advantage of the PON architecture to combine a single OTDR test trace with the OLT output via an automated optical switch.

This is a very compact solution, because the OTDR test signal is combined with the OLT output, and since each OLT covers 32 users these lines can all be monitored by a singe trace. 2000 users can be monitored from a single 19” rack and when this is combined with mapping software fault location is no more difficult than in a point-to-point network. In fact you would need 32 times as many switches to perform the same level of diagnostics on a Point to point system.

EPON Vs BPON Vs GPON

There are several competing PON standards. The ITU promotes BPON & GPON whilst the IEEE backs EPON, which is most commonly used in Japan. The main deference being that B/GPON supports TDM with fixed packet lengths enabling greater Quality of service. Conversely, the IEEE’s EPON standard is an extension of the ubiquitous Ethernet protocol, utilising variable packet lengths for greater bandwidth efficiency.
Japans philosophy is that data demands far outpace Voice, and since the incumbent provider NTT is investing in a core IP network infrastructure, there is good compatibility with EPON solutions. Fujikura’s transceiver division (Sigma Links) concentrates on EPON transceivers including the option to overlay video transmission at 1550nm.

Conclusion

The EPON Vs BPON debate looks set to continue, but as far as the physical infrastructure of PON systems is concerned, all of the elements from simple splices to automated system diagnostics are commonplace in Japan. The demand for broadband in Europe looks set to rise and competition will increase. PON networks could continue to gain ground as a viable broadband option in Europe mirroring the Japanese model.