From VDSL2 to supervectoring (or is that super-vectoring?) and on to NG-PON2, telecom service providers are these days confronted with a bewildering array of technology options for upgrading their broadband networks.
With new standards allowing operators to squeeze ever more juice out of those last-mile copper connections, the need to splash out on a costly fiber deployment has receded, in the view of many telecom executives. Yet the choice between one copper-based standard and another is far from straightforward. The topography of a market may be ill-suited to certain technologies, for one thing. And standards that seem a good bet today might soon lose their appeal.
Those operators taking the fiber plunge are being forced to make similar trade-offs, however. Ronan Kelly, the chief technology officer of broadband equipment vendor Adtran Inc. (Nasdaq: ADTN), reckons existing PON systems will start to come under pressure in the next five to eight years. That means service providers should already be thinking about what comes next. But the equipment needed for NG-PON2 -- which many expect to become the preferred PON standard of the future -- is still prohibitively expensive, according to Kelly. Adtran is now promoting a new technology called XGS-PON as a more cost-effective alternative that could meet needs over the next five to ten years.
Given all the concern and confusion, Light Reading has prepared a two-part guide to the main standards and technology options, whether these are in commercial deployment, trials or at a much earlier stage of development.
This first part examines the technologies that can be use to improve the performance of old-fashioned copper wiring. ADSL and first-generation VDSL have not been covered -- as these are already very mature technologies that are even becoming obsolete -- which makes VDSL2 the first on the list.
Table 1: Summary of Copper-Based Standards
|Standard||Typical architecture||Max theoretical speed||Details|
|VDSL2||FTTC||100 Mbit/s||Extends frequency range to a maximum of 30MHz to provide higher-speed uplink and dowlink connections than older VDSL and ADSL systems|
|VDSL2 vectoring||FTTC||100 Mbit/s on very short loops||Cuts out interference between lines in a telephony cable to improve VDSL2 performance but loses effectiveness over long distances|
|G.fast||FTTdp, FTTC||1 Gbit/s on very short loops||Uses very high frequencies (106MHz in the first version and 212MHz in the second) to support ultra-fast broadband connections|
|VDSL2 profile 35b||FTTC||300Mbit/s at up to 250m (Alcatel-Lucent)||Billed by different suppliers as supervectoring and Vplus, it increases the frequency range of older VDSL2 systems to 35MHz, using the same 'tone spacing' as the widely deployed 17a standard|
So on this and the following pages in this report, we will look at the capabilities, market potential and pitfalls of the technologies cited in teh table above, starting with VDSL2.
Now widely deployed in many European markets, VDSL2 (the VDSL standing for very high bit rate digital subscriber line) is typically used in conjunction with a fiber-to-the-cabinet (FTTC) deployment, with fiber rolled out to the street cabinet and copper wiring used for the final connection to the premise. It comes in a number of different flavors, with successive iterations extending the range of frequencies over which the broadband signals travel and boosting connection speeds for customers accordingly.
Bandwidth claims for VDSL2 vary dramatically, but few vendors trumpet headline speeds of more than 100 Mbit/s on either the downlink or uplink. Even with the latest 30a profile (ratified by the International Telecommunication Union (ITU) as far back as 2006), which uses up to 30MHz of spectrum, service providers are unlikely to be able to support 100Mbit/s connections because of 'crosstalk' -- interference between copper lines in a telephony cable -- and attenuation, which causes signals to lose their intensity over longer distances.
According to Zhone Technologies Inc. (Nasdaq: ZHNE), a small equipment company based in California, the lower-frequency VDSL2 profiles (from 8a to 12b) perform much better over longer loops, even if they fall short of the higher-frequency versions on connection speeds. The 17a and 30a profiles, by contrast, have been used in instances where fiber has been deployed much closer to the customer premise.
VDSL has proven controversial from a regulatory perspective in some European markets. In the ADSL era, asset-light service providers were able to install equipment in an incumbent's local exchange and take control of last-mile connections (so-called local loop unbundling). With VDSL, this unbundling needs to happen at a point that is much closer to the customer premise. Yet sub-loop unbundling -- as it is known -- has not taken off, largely because the economics of deploying equipment in a bigger number of facilities, each catering to a smaller area than an exchange, have been unfavorable. That has driven alternative operators back towards bitstream-based wholesale products, making service differentiation more difficult. (See Europe's Broadband Hangover.)
Next page: VDSL vectoring