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5 9
with
Ian Millner
transmitting and receives the signal from
adjacent pairs as noise.
So here’s the clever thing with vectored
VDSL. Engineers know howmuch noise is
being broadcast by adjacent pairs, so they
can cancel it at the receiving end. This works
because most of the noise when transmitting
vectored VDSL comes from adjacent pairs
that are also carrying vectored VDSL signals.
The problem is when noise received by the
modem comes from an external unknown
source. Figure 3 shows noise from an external
source being induced into one pair. This type
of noise will have an adverse effect on the
speed of the broadband service.
This is the challenge in a building with
two sources of broadband – FTTN and FTTB.
Figure 5 shows two digital subscriber line
access multiplexers (DSLAMs). One is installed
as a node connected to a pillar, and one is in
the building connected directly to the MDF.
The building has a DSLAM, which is
shown as supplying three broadband
services to different apartments. The noise
generated by Provider A’s services cannot be
cancelled by Provider B’s equipment, as it is
‘external noise’, and vice versa.
Consequently the services can be
substantially degraded, leading to loss of the
vectored technology’s benefits.
Communications Alliance is working
on this to minimise the degradation, but
it is generally accepted that two providers
sharing a cable binder will result in lower
data rates.
Should the owners corporation give a
provider permission to install FTTB, as this
may affect overall performance? It’s a tough
one. Getting high-speed FTTB now rather
than FTTN at some future stage could seem
very attractive.
The questions to the FTTB service
provider are:
>
What range of retail service providers
(RSPs) will be available to occupants via
your network?
>
What guarantee can they give the owners
corporation as to service levels when
FTTN is rolled out?
Note that FTTN and FTTB network
providers are limited to providing the
infrastructure. Occupants then need to
contact the RSP to get broadband or other
services installed.
Figure 5.
Top: Figure 3. Bottom: Figure 4.
Node DSLAM
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
External noise
Node DSLAM
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Typical copper cable containing many‘twisted pairs’.
MDF
Node DSLAM
NETWORK PROVIDER A
DSLAM installed next to
and connected to a pillar
Building DSLAM
NETWORK PROVIDER B
DSLAM installed next
to MDF
Vectored VDSL
modems installed in
the apartments
Typical riser cable
containing many
‘twisted pairs’
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem
Vectored DSL Modem