Triple-Play Service Deployment

Chapter 9: Troubleshooting High Speed Data Service
VDSL
In the meantime, VDSL1 and VDSL2 have been certified as
standards by the ITU, using the same DMT concept as ADSL and
ADSL2+ with QAM line coding in the tones as before. VDSL and
VDSL2 use a much larger frequency spectrum making multiple
bands for upstream and downstream transmission possible. This
enables a greater degree of flexibility for higher data rates and
service configurations supporting symmetry between upstream
and downstream rates. VDSL2 uses up to 4,096 tones which are
spaced 4 kHz or, in some cases, 8 kHz apart.
A frequency spectrum of up to 30 MHz in VDSL2 (as opposed to
12 MHz with VDSL1) results in 100 Mbps symmetric data rates to
users within 1,000 feet of the central office. On the other hand,
once reach exceeds a mile, performance degrades to about 24
Mbps, approximately the same level as ADSL2+.
While this migration to VDSL1 and VDSL2 is occurring, packetbased
transport over VDSL is also replacing traditional ATM
technology in order to facilitate Ethernet service all the way to the
customer. Migration to an Ethernet-based architecture such as
VLAN per-service can greatly simplify the network architecture and
reduce network operating costs significantly.
While VDSL offers significant potential advantages such as the
capability to provide much greater bandwidth as well as
symmetric service configurations, new challenges also exist.
Early-stage technology does not guarantee interoperability
amongst differing modem and chip set designs. Further, since
VDSL2 uses a higher frequency spectrum (up to 30MHz), new
noise environments are present which must be understood and
managed. New noise sources, such as short wave radio stations,
and the requirement to not interfere with existing spectrum
usage, such as amateur radio transmitters, makes VDSL
deployment complex. Reach and rate performance not only
depends on the copper loop, but also on spectrum management.
There is still a considerable amount to be learned about VSDL
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