2 Digital subscriber line VDSL2
2.7 Variants of VDSL2 connections

Subsequent chapters deal with the parameters of the block PMD, through which the terminal is connected to the physical transmission medium - symmetric pair.

VDSL2 connection occurs in several different versions so as to be able to perform tasks at various transmission conditions. The annexes to the basic ITU-T G.993.2 is an international standards organization identified three basic types of VDSL2 connections. There is specified in recommendation:

- Annex A - VDSL2 connection to the access network in the North America,
- Annex B - VDSL2 connection to the access network in the Europe,
- Annex C - VDSL2 connection to the access network in the Japan.

Common to all three types of connections is a block arrangement of the internal circuits and principles of these circuits. Thus, for example method of securing data flow of subscriber before its transmission in the access network (circuits for synchronization scrambler, convolution encoder, modulator, etc.).

Multicarrier modulation DMT (Discrete Multi-Tone) is exclusively used for the realization of data transmission for all three types of connections.

The principle of this modulation is used by the division of the entire frequency band into a series of independent subchannels (sometimes also referred to as tones or carriers). Width subchannel may either be the same as the older ADSL therefore 4,3125 kHz or 8,625 kHz twice but only for the 30 MHz band. In each sub-sub-channel data of the subscriber are modulated by QAM modulation. The number of states of modulation at VDSL2 connections from 4 up to 32768, which corresponds to 2 or to transfer 15 bits of one modulation state. The modulation rate is 4,3125 kHz subchannel width set at 4 kBd and 8,625 kHz subchannel width is fixed at 8 kBd. Method FDD (Frequency Division Duplex) can be only used for creation of a bidirectional transmission.

Different profiles, broadcast schedules and frequency masks of PSD (Power Spectral Density) are set for VDSL2 connection in various annexes ITU-T G993.2 according to the typical parameters of access telecommunication networks of the specific region.