Stephen Wilson of Informa Telecoms & Media writes:
VDSL-from-the-central-office (VDSL-FTCO) is becoming an important network strategy for both incumbents and alternative operators, with rollouts becoming commonplace (see fig. 1). Instead of rolling out fiber between the exchange and the subscriber’s home, operators continue to use the existing copper network. This is important, because it can save large amounts of money when compared with rolling out FTTH/B or even FTTC. And operators are increasingly seeing that it is proving difficult to make subscribers pay more for the superfast speeds that FTTH/B can offer. VDSL-FTCO could prove an attractive option for operators looking to boost their speeds, though not to the extent that FTTH/B rollouts would, without breaking the bank.
Fig. 1: Selected VDSL-from-the-central-office deployments
VDSL FTCO dependent on loop lengths
Copper-loop length is absolutely critical for an operator in deciding whether it is worth pursuing a VDSL-FTCO strategy. If the loop length is too long, performance will be little better with VDSL-FTCO than with ADSL2+. In such a scenario, operators may choose to shorten the copper loop by deploying fiber-to-the-cabinet.
Telekom Austria’s deployment of VDSL-FTCO demonstrates the importance of loop lengths.
The operator is deploying VDSL-FTCO to a maximum of 1,500m, and according to vendor Alcatel-Lucent, VDSL2 will provide no improvement in speeds over ADSL2+ from loop lengths of around 2,000m. In addition to loop lengths, cable gauge, or the thickness of the copper wire, will also be an important factor in determining at what point VDSL2 offers no performance benefit over ADSL2+. At shorter loop lengths there will also be questions about whether this technology is really worth investing in, as downstream bit rates will improve but will not be significantly greater than those offered via ADSL2+. Therefore, an operator such as NextGenTel in Norway offers VDSL-FTCO to a maximum copper-loop length of 800m. There is some variation here, with O2 Czech Republic offering VDSL within 1.3km of an exchange.
Whether an operator has already upgraded to ADSL2+ will be a factor in determining whether it is…< …more… >
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