[LINK] 500-Mbits/s over copper
pbrooks-link at layer10.com.au
Thu Mar 19 13:33:15 EST 2009
Tom Koltai wrote:
> The problem for Australia is that each Residence has two pairs only, and
> the average home is further than 500 metres from the exchange.
> There are four ISP's utilising this technology in Australia, however
> only one so far has offered phone combined (EFTEL) - which would be
> necessary to take advantage of the pair bonding Ericsson implementation.
I think you are confusing bonded VDSL2 with bonded SHDSL Tom.
Several ISPs are using bonded SHDSL (one vendor Hatteras, others are
available) to achieve relatively high bandwidth symmetric links over
distances of a kilometre or two. SHDSL (whether bonded or not) uses the
low frequency spectrum and prevents a simultaneous baseband telephone
service from operating. If EFTel are providing a combined phone service,
its probably using VoIP within the broadband channel, which the others
could presumably also do - and it has nothing to do with pair-bonding.
None of this has anything to do with the Ericsson announcement, which is
pair-bonded *VDSL2*, and more importantly is a demonstration of
vectorisation, which is a fancy word for interference cancellation
similar to the MIMO techniques used in modern radio networks. This has
the potential to vastly improve even single-pair VDSL2 services (and
even ADSL services as well).
Today's ADSL/VDSL technology works through interference avoidance -
active interference cancellation aka vectorisation has been a hot
research topic for a few years, and its good to see it start to emerge
from the labs.
> The result at 12-15mhz would be between 10 and 20 mbits per subscriber
> (using bonded pairs = 4 copper wires) at no more than 1.5 kilometres
> from the exchange. Therefore the NBN cabinet rollout would be an
> imperitive if we want the majority of Australians to have over 50 mbit
> to the home.
Not really. Even with an NBN cabinet rollout, your very first sentence
still applies - most residences have only one or two pairs from the
piller into the residence. The Ericsson demonstration used six pairs
bonded together - for this 500Mbps speed to be available for widespread
residential use, you would still have to run more physical copper
drop-cables to each house so that every one of them had many pairs to
bond together - and if you're going to do that, you'd be better off
making at least one of those pairs of glass rather than copper.
Yes, this demonstration indicates that the two pairs into each house
might be bonded together to form a double-bandwidth VDSL2 service - but
then, line bonding was built into the ADSL2 and 2+ spec as well, and we
don't see any bonded-ADSL2+ services in the commercial marketplace today
- three-pair-bonded-ADSL2+ could achieve 50 Mbps+ today if the software
in the DSLAM and a suitable CPE supported it.
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