WHAT IS HDSL, SHDSL?

HDSL (HIGH BIT RATE DIGITAL SUBSCRIBER LINE)

The ITU G.991.1 standard was the first DSL technology to utilize the high frequency domain on copper twisted pair cables. In the US, high-speed synchronous circuits were born as a technology working mainly on T1 carriers to carry local telephone carrier lines, as well as converged data lines and voice channels. The first T1 carrier lines used AMI (alternate Mark Inversion) line coding, which was changed to B8ZS coding because of distance problems, but the need for repeaters at 1-1.2 mile intervals and the energy problems for this continued.

It was in the US that the first Dhdsl_spectrum-2SL technology was used to solve the problems. The 2B1Q line coding technique was used, which allowed a data transmission rate of 784 Kbps over a twisted pair of cables. Over 2 twisted cable pairs, a bandwidth of 1.544 Mbps was achieved. Although this technology immediately attracted the attention of the industry, it took some time for widespread use in the world due to the difference between E1 and T1 lines. New standards were set by the ITU and standardized as G.991.1 technology under the name HDSL. With these standards, a maximum bandwidth of 2.0 Mbps was achieved using CAP (Carrierless Amplitude Pulse Modulation) over two twisted cable pairs.

HDSL made it possible to reach much greater distances than T1 without the use of repeaters (also called T1 without repeaters). With 24 gauge cable, it could provide service up to 12k feet without a repeater and 60k feet with a repeater. In the first case, POTS service could not be provided, but with the new generation of HDSL standards, it is possible. HDSL can be used at both T1 and E1 speeds. And it can be channelized in multiples of 64k, making it suitable for lower bandwidths.

HDSL was the basis for HDSL2 and SDSL and then SHDSL.

HDSL2

It is the 2nd Generation HDSL standard with a 6dB noise limit. It offers the same bandwidth as HDSL. The difference is that it works over a single twisted pair cable and is more resistant to distance and cable thinness and poor quality.

SDSL (SYMETRİC DIGITAL SUBCRİBER LINE – SYMETRİC DIGITAL SUBSCRIBER LINE)

It is a type of DSL that works with E1-T1 carriers. Service can be provided up to 3km over a single twisted pair of cables. It uses the entire bandwidth of the same cable, which cannot be used in conjunction with conventional voice service.

SDSL is a proprietary technology, not explicitly standardized. Therefore it usually only works between devices from the same manufacturer. It is the predecessor of G.SHDSL (G.991.2), standardized by ITU-T in February 2001. In Europe, G.SHDSL is standardized as “SDSL” by ETSI.

SHDSL-G.SHDSL-G.SHDSL.BİS

Also known as G.SHDSL. It was published by the ITU in February 2001 as the ITU-T G.991.2 standard. In December 2003, it was published again by the ITU as the enhanced G.991.2 and this enhanced G991.2 standard is also known as G.SHDSL.bis or simply SHDSL.bis.

It can operate at data transfer rates from 192 Kbps to 2,304 Kbps symmetrically with one twisted pair cable and from 384 Kbps to 4,608 Kbps with two twisted pairs. Enhanced SHDSL Mode can offer symmetrical bandwidth up to 5696 Kbps over a single twisted pair cable. SHDSL is suitable for PBX, VPN and web hosting services for companies. T1 or E1, Multiple ISDN BRA (Basic Access Rate), ATM trunks or Ethernet packets can be carried over SHDSL and SHDSL bandwidth can be shared to 2 of them in multi-carrier mode.

DIFFERENCES OF G.SHDSL.BS FROM G.SHDSL

Support up to 4 twisted pair cables
Support for bandwidth up to 5696 kbps as defined in Appendix F.
Support for Dynamic Rate Repartitioning as defined in Appendix E.10.3, which allows SHDSL data rates to be changed flexibly without service interruption.
New data transport definitions including PTM (Ethernet Packet Transfer Mode) as defined in Appendix E.11.