Broaderband? The future of high-speed access

In the three years since BT launched ADSL in the UK, the speeds on offer have remained the same but encouragingly the cost has declined by a third.

This may sound like a good deal for the consumer until you realise that in the same period PCs and other devices such as digital cameras, media players and printers have tripled in speed and more than halved in price.

But while the broadband services currently available remain essentially static, the technology is being continually enhanced by faster systems with longer reach, more flexibility and greater ease of management.

Two standards finalised this year are enhancements of ADSL -- ADSL 2 and ADSL 2+. These increase the maximum downstream speed to 12Mbps and 25Mbps respectively, and retain compatibility with the earlier ADSL standard. The increases in speeds come from improved modulation techniques and better signal processing, while ADSL 2+ combines those with an extra set of carrier frequencies; ADSL 2 also manages an extra 200 metres of range, while the extra speed of ADSL 2+ works up to over 1.5 kilometres.

ADSL2/2+ has a lot more diagnostic information, supports channelised voice -- so multiple virtual phone lines can be carried over one real copper pair -- and has various power-saving modes. It can also add an extra 256Kbps upstream by taking over the bandwidth previously reserved for the old telephone voice service, and can bond multiple phone lines to increase the total bandwidth.

One of the oldest contenders for next generation broadband is VDSL, which has been gently cooking in the laboratories for around a decade. By using much higher frequencies than DSL, it gets much higher speeds -- up to 52Mbps downstream and 16Mbps up -- but at a great cost in range, typically around 1000 metres maximum. This makes VDSL most attractive in situations where fibre can be brought close to a lot of users -- hence it has been most popular in the Far East where urban population densities are very high. However, it has suffered from a prolonged standards battle between backers of two forms of modulation, DMT and QAM, and problems with crosstalk and other interference when a VDSL line shares a bundle of cables with ADSL and other techniques. VDSL is settling down -- in a recent independent no-holds-barred test, DMT outperformed QAM, and this result has encouraged some vendors to choose the former.

The other major networking technology with the potential to usurp current broadband is wireless. Here, two initiatives -- 802.16 for fixed and 802.20 for mobile -- are going through accelerated approval. 802.16, also called Wimax, will be able to deliver up to 100Mbps and 802.20 around 1Mbps. 802.16 has a maximum range of around 30 miles, and is intended to complement wired broadband by being quick to deploy and easy to set up for places out of the range of DSL. As nobody's made any money out of previous varieties of wireless broadband, the jury's out on whether this is a sensible business model.

Higher speeds per se aren't interesting to the telcos, who have been very reluctant to sell the existing technology at anything like its full speed of 8Mbps. The higher speeds -- 6Mbps and 8Mbps -- are only available in the UK from companies such as Easynet and Bulldog who have bought unbundled lines from BT. Local Loop Unbundling (LLU) was expected to provide a boost to alternative, faster DSL services as it takes control of the telephone line away from BT: however, there's been little take-up. Nonetheless, this is probably the mechanism by which future very fast broadband services will be initially deployed.

One standard that is attempting to tie together many strands of next-generation broadband access is 802.3ah, Ethernet in the First Mile (EFM). Originally called Ethernet in the Last Mile -- the change was made for marketing reasons -- this IEEE group intends to make Ethernet the ubiquitous protocol for future broadband.

To that end, 802.3ah defines four areas of interest. Point-to-point copper, which is where ADSL currently operates, will have two speeds -- 10Mbps at up to 750 metres, and 2Mbps at up to 2700 metres. Point-to-point fibre will support 1Gbps or 100Mbps; point-to-multipoint fibre describes how to multiplex many connections onto a single fibre. Finally, 802.3ah includes explicit operation, administration and maintenance (OAM) standards for error testing and remote management.

The core technologies were approved in late July by the IEEE committee: most notably symmetric DSL -- G.SHDSL -- for the 2Mbps and VDSL-DMT for the 10Mbps. The idea is that by making the back end of broadband distribution systems pure Ethernet, the cost of provisioning goes down dramatically: however, the committee has seen more than adequate levels of dispute between various camps in both the carrier and the chip making areas.

Many of the aspects of the various standards have been designed to reduce cost of commissioning and deployment, not just to maximise speed. Also, new services that will need higher bandwidths than those currently deployed have been slow to suggest themselves: currently, hopes lie in multiple video stream services. Although there are many business benefits from faster, more efficient broadband communications, experience has shown that only the massive deployment of new technologies in the consumer market creates the environment where telcos feel able to offer them at reasonable prices to bigger customers.