What is vDSL?
VDSL (Very high speed Digital Subscriber Line) belongs to the xDSL family of technologies. It is mainly used for digital subscriber lines in which a very high transmission speed is required. In the solution based on VDSL a central system point is a dedicated commutative system receiving transmitted data from a source (e.g. from a fiber-optic cable), and then with the use of classic copper cabling transmitting data to a target user. The rule of functioning of the ADSL technology is based on using a wide frequency band of signals transmitted via copper cabling and four-ply intensifying of the used bands, in order to separate particular channels. A lower final frequency is 300 Hz (however, in practice 350 KHz is acceptable) in case of lack of a necessity of transmitting the analogue phone signals. An upper boundary depends on cabling segment’s length, and amounts to 30MHz for a cable which does not exceed 300 m to 100 MHz, with a five-hundred-meter cable.
These technical solutions allow to gain very high bandwidths, but on relatively short cabling segments:
- 56 Mb/s on segment up to 300 meters (in practice segments that do not exceed 200 meters are used).
- 25 Mb/s on a distance of 300 – 900 meters.
- 10 Mb/s on a distance up to 1500 meters.
After exceeding 1500 meters the bandwidth offered by VDSL becomes lower than in case of using the ADSL technology, thus the solutions based on VDSL are not used on higher distances. The extension of VDSL is technology named VDSL2. Multiplexing with a division of signal frequency has been used in this technology. It has also been based on a full frequency band up to 30 MHz. The solution of this type allows enlarging a possible to obtain bandwidth. However, similarly to the case of the predecessor it happens on short distances:
- Up to 200 Mb/s, on a segment which does not exceed 300 meters (like in VDSL 200 meters are practically not exceeded).
- 100 Mb/s on a segment of 500 meters.
- 50 Mb/s on a segment up to 1000 meters.
Above 1500 meters a bandwidth possible to obtain is very close to the one using the ADSL technology, and remains on a similar level to a distance of 4 -5 kilometers. Therefore, it can be assumed that in future the VDSL2 will gradually drive the ADSL out of the market. However, the biggest disadvantage of the VDSL2 is a necessity of using high-quality cabling, of strictly defined physical parameters, especially on the shortest two hundred-meter segments. These requirements clearly raise total costs of installing the VDSL2, and in rather small areas of using, their economic sense becomes disputable.