Symmetric Digital Subscriber Line

SDSL ( Symmetric Digital Subscriber Line ) is a broadband access technology at a public digital network, such as the telephone network via a telephone line. Unlike ADSL, data can be transmitted at the same speed in both directions. SDSL is mostly used by business customers as well as for connecting network components of the network operator.

Features and Functions

The SDSL technology is designed by network operators for high bit rate data transmission in the wireline local loop evolution of HDSL technology and was originally used primarily for connecting network components in the access network and the provision of primary multiplex connections of the ISDN. The difference HDSL is the advanced modulation technique of SDSL. So far, a SDSL variant is primarily used, which uses a pair of copper wires with a max. Bit rate of 2.36 Mbit / s and to the prevailing ADSL variants significantly higher range of up to 8 km. Variants for two pairs (bonding) are also available and achieve greater ranges. As an alternative to copper wires is a transmission via optical fiber ( 2 Mbit / s, 11 Mb / s) possible.

The term " symmetrical" refers to the direction of function of the data rate: unlike ADSL SDSL only supports modes that operate in both directions with the same data rate. Contrast, ADSL works with " asymmetric ", ie directionally different data rates between the user and the access point. The data rates of SDSL are integer in the devices used multiples of 64 kbit / s: 192 kbit / s up to 2.304 Mbit / s Note that by means of traffic shaping and SDSL connections can be provided with asymmetric data rate.

SDSL is with regard to crosstalk ( crosstalk ) compatible with services such as POTS, ISDN or other DSL technologies. Pairs, is transmitted through the SDSL can be routed in the same cable bundle, but not in the same star-quad, as these Verseilungsart is not suitable for SDSL. As a line code trellis Coded Pulse Amplitude Modulation used (TC- PAM).

SDSL does not support the splitter technology using ADSL. For ADSL POTS and ISDN service can ( the " Splitter" ) are coupled via a crossover, because ADSL is located only in the frequency range above the POTS and ISDN services. In contrast, SDSL uses the whole frequency range - even the ADSL reserved for telephone service low-loss, high-reach lower frequencies. Therefore, a conventional telephone service can be transmitted at SDSL on the same wire pair; So it is with SDSL is a pure data connection. However, the SDSL bandwidth used by a plurality of multiplexed channels simultaneously. This could be for example, several B- channels for ISDN connection. In addition to telephony SDSL connections can Generation Network architectures are provided via IP telephony and next.

SDSL was standardized not only by the European Telecommunications Standards Institute (ETSI ) under the standard TS101524, but also by the ITU under the standard G.991.2, but under the name SHDSL Single - Pair High - Speed ​​Digital Subscriber Line ( SHDSL ). Usually it is in the SDSL connections today installed in Germany by connections after this G.SHDSL standard.

A and S in the names have nothing to do with asynchronous or synchronous data transfer. ADSL and SDSL are each transmission standards for asynchronous transmission.

Device technology

SDSL lines can be established not only with SDSL NTs now, but there are also bridges and routers with SDSL interface. For long distances SDSL repeaters are available which do not only regenerate the signal in contrast to the usual repeater technology, but also control a number of monitoring functions.

For transmission over fiber optic lines corresponding media converter can be used, which convert about a local S2M ( PRI ) connection to an optical SDSL line.