The full form of VDSL is Very-high-bit-rate Digital Subscriber Line.

Very-high-bitrate digital subscriber line (VDSL) is a DSL technology that offers an upstream rate of 12 Mbps and a downstream rate of 52 Mbps. VDSL is considered to be the next-generation DSL that provides a complete package for home communication and entertainment.

very-high-bit-rate digital subscriber line”, “VDSL” or “VHDSL means a DSL standard that provides high speed Internet access, being an improved version of ADSL (asymmetric DSL) that typically offers download speeds of up to 52 Mbps and upload speeds up to 16 Mbps, and operates over a single flat untwisted or twisted pair of copper wires or on coaxial cable;

VDSL (Very High Bit-Rate Digital Subscriber Line)
Broadband has revolutionized the way we view and use the internet. The two
main types of broadband technology that have pervaded the market are
Asymmetric Digital Subscriber Line (ADSL) and cable modems. Both these
technologies are a huge leap from the days of the 56 Kbps dial-up connections,
with maximum speeds ranging between 8 to 10 Mbps. This makes one wonder,
what’s next?
Another form of DSL, known as VDSL or Very High Bit-Rate Digital Subscriber Line,
is widely regarded as the next step in Internet connectivity. This technology is
capable of providing incredible bandwidth with download speeds up to 52 Mbps
and upload speeds of up to 16 Mbps.
The architecture of VDSL can be based on two different technologies:
1. Quadrature Amplitude Modulation (QAM)
2. Discrete Multitone Modulation (DMT)
QAM and DMT are not compatible with each other, and DMT seems to be the
technology of choice with current equipment manufacturers. A VDSL connection
based on DMT architecture consists of 247 virtual channels populating the
available bandwidth. The integrity of each individual channel is constantly
monitored; if the signals from a particular channel degrade, the data is
transferred to an alternate channel. In this fashion, data is constantly shifted
across channels in a VDSL network, ensuring that the best route is chosen for the
transmission/receipt of data. VDSL can operate over the existing copper wires of a
phone line just like ADSL, with amazing speeds, but with a serious limitation – a
VDSL connection is viable over copper lines for only short distances, i.e., 4,000
feet or 1,200 m. But, this limitation is being inadvertently overcome by telecom companies who are replacing copper lines
with fiber optics.

Most companies are implementing FTTN – Fiber To The Neighborhood, which
installs a fiber optic line from the company’s end to the main junction box in a
particular neighborhood. Telecom companies plan to extend this further to FTTC –
Fiber To The Curb, which involves replacing copper wires with fiber optics right up
to the point where individual residential phone lines branch off.
If a certain part of the line between the telecom company and the customer is
replaced with fiber optic cable in the manner described above, the VDSL signals
are “lost in translation”; they are converted from analog signals that traverse the
copper lines to digital signals that run along the fiber optic cables, and then back
to analog again. Installing a VDSL gateway at the junction box will convert the
VDSL signals to pulses of light that can travel through the fiber optic cables. When
the telecom company end receives the light impulses via the fiber optics line, it
responds by sending data back to the junction box gateway. The gateway
converts the received data into analog format again and sends it to the
customer’s VDSL modem through a short copper line. This process eliminates the
distance barrier that arises in a copper line based VDSL connection and makes
long distance VDSL connectivity viable.