Symmetric Digital Subscriber Line
SDSL ( Symmetric Digital Subscriber Line ) is a DSL access technology to a public digital network such as the telephone network via a telephone line . In contrast to ADSL , data can be transmitted in both directions at the same speed. SDSL is mostly used by business customers and to connect network components of network operators .
Features and functions
The SDSL technology is one of network operators for the high bit-rate wired data transmission in the local loop designed development of HDSL technique and originally served primarily the connection of network components in the access network and the provision of primary rate interfaces of ISDN . The difference to HDSL lies in the advanced modulation technology of SDSL. So far, an SDSL variant has been mainly used, which uses a copper pair with a max. Bit rate of 2.36 Mbit / s and a significantly higher range of up to 8 km compared to the predominant ADSL variants . Variants for two pairs of wires ( bonding ) are also available and achieve greater ranges. As an alternative to copper wires, transmission via glass fiber (2 Mbit / s, 11 Mbit / s) is also possible.
The term "symmetrical" refers to the directional dependency of the data rate : in contrast to ADSL , SDSL only supports operating modes that work in both directions with the same data rate. ADSL, on the other hand, works with "asymmetrical", that is, data rates in different directions between user and access point. The data rates of SDSL in the currently available devices are integer multiples of 64 kbit / s: from 192 kbit / s up to 2.304 Mbit / s. It should be noted that SDSL connections with asymmetrical data rates can also be provided using traffic shaping .
SDSL is respect crosstalk ( crosstalk ) compatible with services such as POTS , ISDN or other DSL technologies. Twisted wires over which SDSL is transmitted can be routed in the same cable bundle, but not in the same star quad , as this type of stranding is not suitable for SDSL. As a line code is Trellis Coded Pulse Amplitude Modulation (TC-PAM) used.
SDSL does not support the splitter technology that ADSL uses. With ADSL, POTS and ISDN services can be decoupled via a crossover (the " DSL splitter "), since ADSL is only located in the frequency range above the POTS and ISDN services . In contrast, SDSL requires the entire frequency range - including the low-attenuation , high-range lower frequencies reserved for ADSL for telephone service . Therefore, with SDSL, no conventional telephone service can be transmitted on the same wire pair ; SDSL is therefore a pure data connection . However, the SDSL bandwidth can be used by several multiplexed channels at the same time. For example, this can be several B channels for an ISDN connection. Telephony can also be provided on SDSL connections using IP telephony and Next Generation Network architectures.
SDSL has not only been standardized by the European Telecommunications Standards Institute (ETSI) under the TS101524 standard, but also by the ITU under the G.991.2 standard, but under the name SHDSL: Single-Pair High-Speed Digital Subscriber Line (SHDSL) . As a rule, the SDSL connections installed in Germany today are connections according to this G.SHDSL standard.
A and S in the naming scheme have nothing to do with asynchronous or synchronous data transmission. ADSL and SDSL are transmission standards for asynchronous transmission.
Device technology
SDSL lines can now not only be set up with SDSL NTs , but there are also bridges and routers with SDSL interfaces. For long distances, SDSL repeaters are available which, in contrast to the usual repeater technology, not only regenerate the signal, but also master a number of monitoring functions.
Appropriate media converters can be used for transmission over fiber optic lines, which convert a local S2M (primary rate) connection to an optical SDSL line.