2 Digital subscriber line VDSL2
2.1 Basic features of VDSL2 connection

Digital subscriber line VDSL2 is a second generation of VDSL connection. However, significant and proven innovation is not surprisingly taken from its original specification of VDSL, but it is taken from the second-generation connection ADSL2. This is particularly the grid encoding (known as Trellis Code) for the ability to repair the receiver single bit errors and the ability to correct error bursts caused by the impulse interference using a Reed-Solomon code and data interleaving. Like ADSL2 transmission speed can be changed during operation SRA (Seamless Rate Adaptation), controlling the transmission power to reduce crosstalks to neighboring pairs, and activate power saving mode (known as Sleep Mode).

The basic recommendation which standardizes the connection of the VDSL2 is ITU-T G.993.2.

Increasing the transmission rate to obtain an extension utilized frequency band up to 30 MHz. For comparison, ADSL2+ connection uses a frequency band only up to 2,208 MHz. Maximum transmission speeds ranging from tens to hundreds of Mbit/s. In the downstream direction, the maximum value of around 200 Mbit/s.

However, extending of utilized frequency band has one big disadvantage. The maximum length of the local loop, which can be operated on VDSL2 connection, is shorten in comparison with ADSL2+ connection. The attenuation of line in specified frequency band is growing with increasing frequency bandwidth.

The next figure shows the attenuation course of the twisted pair depending on the frequency (cable length 1 km, average live wires 0.4 mm, copper material). Symmetrical pair is located in a classic local quad cable in construction TCEPKPFLE.