2 Digital subscriber line VDSL2
2.3 Layer model of terminal equipment at VDSL2 connections

Functions and features of terminal equipment at VDSL2 connections can be described similarly as for other xDSL, through a layer model. The device model includes two basic parts. The first part is independent on the data transmissions, because it contains the functions and blocks that are all end devices associated with the same and adapting the physical data transmission medium. There are blocks of PMD (Physical Media Dependent) and PMS-TC (Physical Media Specific - Transmission Convergence). The second part, block TPS-TC (Transport Protocol Specific - Transmission Convergencer) respects the type of data transfer and the structure of subscriber data and it is depended on the data transmissions.

Layer model of terminal equipment at VDSL2 connections.

The basic function block PMD are linked to the actual transmission of signal transmission environment. There are mainly generating and recovery cycle, modulation and demodulation, echo cancellation, compensation of the negative line parameters and initialize the connection.

Block PMS-TC is specific depending on the transmission environment and perform functions associated with creating frames, frame synchronization, data security realized by FEC (Forward Error Correction), interleaving, scrambling and descrambling. There are also in this block the additional subscriber service information added into a bit stream (header of data frames) and implements the service communication between devices.

Parameters of TPS-TC block depends on the desired functionality of the terminal device or the type of carried data traffic (type of requested services). Block TPS-TC serves as an adaptation block the transport protocol (format of user data), and other lower blocks of VDSL2 connections. It is responsible for multiplexing, demultiplexing and synchronization of the individual subscriber data that flows according to the required quality of service parameters (flow prioritization of certain services).

Reference points labeled as S/T are interfaces in the direction to user terminals. The description of the parameters of VDSL2 connections will proceed just a block from the TPS-TC towards the block and PMD interface U.