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Fibre-to-the-home provides not only the bandwidth for broadband but also the economy to compete with copper.
By Mark Telford
Although optical fibre is deployed in long-haul, wide-area and metro-area networks, most residential communities still rely on copper-based technologies such as twisted pair, HFC and xDSL for broadband access to the Internet. However, as emerging applications require greater bandwidth, these are causing a "last-mile" access bottleneck.
In the past, a fibre-to-the-home (FTTH) solution was too expensive, as well as being incompatible with analogue TV. But deployment of LAN networks, such as Ethernet over fibre, now offers data speeds up to hundreds of Mbit/s for voice, video and data signals, as well as a longer life-span. At the same time, technology developments have led to cost reductions in support equipment. For example, rather than one fibre per home, resource sharing circuits in Passive Optical Network-based FTTH now allow multiple (N-way) distribution to many homes (see panel).
Ericsson's approach to FTTH
Rather than FTTx architectures - which use VDSL for the final connection - Ericsson Network Technologies' "true" FTTH solution uses entirely Ethernet-over-fibre technology, says fibre access Product Manager Peter Lo-Curzio.
With the focus on getting the business case right, it uses the least expensive optical elements: two fibre pairs for each home, 95% of it multimode (for links up to 1km in length) with single-mode only where necessary, such as in rural areas. Enhanced multi-mode fibre enables future upgrade from 100Mbit/s to Gbit/s for each apartment by changing end-user and active node electronics.
Currently, there is "no reason to use Gigabit data rates", says Lo-Curzio, since 100Mbit/s is sufficient for more than 20 TV channels simultaneously. But, he adds, optoelectronic component development is such that "in perhaps five years there will be no cost difference between 100Mbit/s and Gbit/s rates" when adoption will depend just on the services and content available.
The main service initially is fixed, symmetrical high-speed Internet access for home entertainment, small businesses and home-based working. Ericsson is starting to implement systems for emerging services such as digital CATV, voice-over-IP and telemetry, for individual users to monitor and reduce consumption of utilities. IP TV, described as the "most important application", will be available soon.
Ericsson's first FTTH installation was begun in January 1999 on an estate of 824 flats in 22 multi-storey buildings in Hasta, Hudiksvall, Sweden as a joint venture with construction company Hudiksvalls-bostäder AB (see following section). Though initially a trial network, Ericsson now operates it on a commercial basis, incorporating connections to 2000 apartments.
Whereas the Hudiksvall installation used 850nm transponders, subsequent installations in Sweden employ 1300nm transponders to increase the length of the link from central office to end-user. This reduces the number of active connection nodes and hence cuts expensive maintenance costs.
A second installation, begun in 2000 in the town of Sundsvall for the company Norrporten, features 800 connections. Future expansion is expected throughout Norrporten's customer base.
A third, in Vallingby, Stockholm, started in January 2002 and due for completion in November for Svenska Bostader AB, incorporates 5000 connections (4500 apartments & 500 businesses).
Kurt Hamrin, Ericsson Network Technologies' Manager Access Networks, says that demand for such installations is driven by the Swedish government's ITC-Commission (www.itkommissionen.se) which has made a recommendation for transparent networks. Thus, a communications operator acts as a neutral broker in buying services from operators, which are therefore required to compete, pushing prices down.
While Ericsson is currently building the passive optical network, the active elements are being installed by communications operator Birka Energi, a Swedish power company, which will also manage maintenance and billing of the network.
Hamrin adds that Ericsson is also involved in FTTH projects in other countries, including Denmark (involving several municipalities and property owners), Holland and Italy.
According to Karin Nygard-Skalman, Solution Marketing manager at Ericsson Network Technologies, the barriers to demand are the need to develop video and TV distribution technology, and the lack of services. However, while she acknowledges that copper-based ADSL is a "good technology for Internet access" and that incumbent telecoms carriers want to further utilise their existing networks, the availability of high-bandwidth services should drive up demand for FTTH. In particular, Ericsson is targeting greenfield developments by property owners and power companies which do not have existing networks.
PON-based FTTH network installation
The Hudiksvall network is based on an active double-star topology (Fig. 2) radiating from a central area node which is directly connected to the metropolitan area network. The network connects buildings by single-mode fibre ribbon cables terminated in active house nodes in the basement. Radial architecture provides direct connections from each apartment to the house node (by 2x50/125mm Gigabit-grade multi-mode fibre), eliminating costly horizontal cross connection.
A pre-requisite was that the initial cost of passive parts should be close to that of a traditional CAT5 copper network. This can be achieved via a combination of:
- Blowing fibre ribbons with factory-fitted connectors from each apartment through a microduct system to a central splice cabinet in the house node (Fig. 3).
- Using factory-tested fibre ribbon cable spliced to pre-terminated patch-cords from the access node to the splice cabinet, where mass fusion splicing is carried out. This eliminates splicing or field termination/polishing of connectors in each apartment, saving about 20 minutes of installation time per apartment. Since neither patch cords nor panels are used, materials cost (the passive fibre network in the building) is cut by at least 30%.
Bundles of microducts containing 7 or 12 units are mainly installed in existing power cable risers, pulled to each floor level, and fanned out to flats. Suppressing costs while ensuring durability precludes the use of optic wall outlets, so connectors are mounted in a small protective subscriber terminal box and attached directly to a medium converter.
Compared to cable pulling, blowing fibre has several advantages:
- Fibre cables are sensitive to sharp bends and tensile loads and difficult to splice, but microducts are not affected during installation. When the duct system is in place, blowing takes a few minutes. The fibre is relaxed in the duct and not affected by any harsh treatment during installation. As blowing fibre is a point-to-point connection, no intermediate fibre spicing is required.
- Splicing is faster for microducts than for cables, so installation is up to 30% faster than for pulling cables.
- Fibre ribbon is more rugged than separate fibres and identical to that in standard ribbon cables (but wrapped in aramide yarn, which increases the cross-sectional area exposed to the driving air and reduces friction against the duct).
Also feasible is an incremental deployment, whereby empty tubes are installed and fibres only blown in to subscribing apartments.
Fibres can be replaced quickly by blowing them out, allowing flexible installation such as the simultaneous replacement of multi-mode fibre and deployment of single-mode fibre.
The Hudiksvall project shows that - compared to copper cabling - in a multi-storey residential area large FTTH installations are feasible and cost effective.
FTTH is deployed in two main architectures:
- Point-to-point, which needs one optical transceiver per subscriber at the central office (CO) and is generally deployed to businesses in metro areas.
- Passive optical network (PON), which allows a fibre from a single transceiver in the CO/head-end to be split 32 ways. With the only other active electronics at the customer premises endpoints and only passive components in between, PON is more cost-effective for small-to-medium-sized businesses and residences.