2 Digital subscriber line VDSL2
2.4 Data transmission modes of subscriber terminal

Parameters of TPS-TC block in the layer model of terminal equipment are closest to the participant and meet their functionality requirements depending on the type of data transfer of the subscriber. In current VDSL2 connections supports block TPS-TC three modes of data transfer:

- STM (Synchronous Transfer Mode). In this mode, all end devices work in the part of access network synchronously depending on the DSLAM. Synchronicity means that data transmissions along the upstream and downstream are carried out on all terminals at the same point in the same time.

The advantage of this transmission mode is the significant reduction of near end crosstalk noise.

- ATM (Asynchronous Transfer Mode). This method of transmission ensures backward compatibility with existing ADSL connections (ie. dual VTU-R can work against ADSL DSLAM). For data transmission using the cell constant length of 53 bytes, which are transmitted according to the type of content and inserted with the relevant virtual path and channel identifiers VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier).
- PTM (Packet Transfer Mode) is designed for efficient transmission of streams in which the subscriber data are encapsulated into packets or frames. Typically, this is the Ethernet frame protocol frame Point-to-Point packets or MPLS (MultiProtocol Label Switching).

- PTM scheme is based on standards known as Ethernet in the First Mile (IEEE 802.3ah), namely solutions for metallic access network based on the 10-TS-PASS.

VDSL2 connection may above the physical layer to support multiple independent data channels includes more services which have a different quality of service requirements. Typically it can be a video transmissions which it is necessary to prioritize traffic in preference with normal data. The data of these services are transmitted via two independent pathways (differentiated by latency path) with independently adjustable parameters such as the depth of interleaving and therefore the delay (dual latency), etc.

Quality of service is a scale how to evaluate the subscriber satisfaction with the service that he pays for, and that it provided by the operator. Evaluation of services is a relatively complicated process. The different criteria are used for the evaluation. For example, starting from a completely objective technical criteria, such as achieving a transmission speed or delay of transferred data, and ending with a completely subjective criteria such as clarity bill or satisfaction with customer support.