2022-06-16 0

What is xDSL Technology

Hello, everyone!

Today, I’d like to share with you some knowledge about xDSL technology.

xDSL is a general term for various types of digital subscriber line (DSL), including ADSL, RADSL, VDSL, SDSL, IDSL, and HDSL. xDSL is a new transmission technology. It uses high frequency and modulation technologies on existing copper telephone lines, that is, the signal processing technology that adds or obtains more digital data to analog lines can achieve a high transmission rate (theoretical value can reach 52 Mbit/s). The biggest difference between DSL technologies lies in the signal transmission rate and distance, and the symmetry of upstream and downstream channels.

  • Integrated Services Digital Network (ISDN) technology is the first-generation DSL technology. It has two interface rates: BRI and PRI, the BRI can reach 144 kbit/s, and the PR can reach 2.048 Mbit/s or 1.544 Mbit/s. ISDN is a communication network developed based on the digital telephone network IDN. ISDN supports multiple services, including telephone service and non-telephone service.
  • HDSL technology means High Bit Rate Digital Subscriber Line, which enables 2.048 Mbps or 1.544 Mbps transmission rate. HDSL is an early developed and widely used xDSL family and is a mature DSL technology. It features good interconnection, long transmission distance, low equipment price, excellent transmission quality, low bit error rate, and low interference to other line pairs. The line does not need to be reconstructed. It is easy to install, maintain, and manage.
  • Asymmetric Digital Subscriber Line (ADSL) is a technology that uses existing traditional telephone lines to transmit digital information at a high speed. The ADSL technology uses the existing pair of telephone copper lines to provide users with asymmetric transmission rates in the upstream and downstream directions. The asymmetry is mainly caused by the asymmetry of the upstream rate (up to 640 kbit/s) and downstream rate (up to 8 Mbps). The uplink (from the user to the network) is a low-speed transmission, which can reach 640 kbit/s. The downlink (from the network to the user) is a high-speed transmission, up to 8 Mbit/s, nearly 300 times that of the traditional 28.8 kbit/s analog modem, and 70 times that of the 128 kbit/s Integrated Service Data Network (ISDN).
  • Very-high-bit-rate Digital Subscriber loop (VDSL) is the fast version of ADSL. VDSL can run at symmetrical or asymmetrical rates, with the maximum symmetrical rate of 26 Mbit/s in each direction. Other typical VDSL rates are 13 Mbit/s symmetrical rates, 52 Mbit/s downstream rate, 6.4 Mbit/s upstream rate, and asymmetrical rate combinations.VDSL technology uses frequency division multiplexing technology. Data signals and telephone audio signals use different frequency bands and do not interfere with each other. Users can make or receive calls while accessing the Internet.
  • VDSL2 is a communication technology similar to ADSL and ADSL2+. It uses the DMT modulation mode, but the frequency range is increased to 30 MHz, providing a bandwidth of up to 100 Mbit/s
  • G.fast (also called Giga DSL) makes it possible to achieve the FTTH access rate using existing copper lines, bringing copper line access to the gigabit era.
  • DSLAM: Digital Subscriber Line Access Multiplexer. The DSLAM is a central office device of various DSL systems. It receives all DSL lines and aggregates traffic
  • In the xDSL access network, splitters are used at the CO and CPE to separate and combine low-frequency and high-frequency signals. The low-frequency voice signals are connected to the PSTN (public switched telephone network) switch or POTS (plain old telephone service) phone through the splitter to transmit common voice information. High-frequency digital signals are sent to the DSLAM or DSL modem.
  • With the increase of the spectrum width, the crosstalk between copper lines increases sharply and the transmission distance becomes shorter. Initially, the voice signals carried by copper lines are low-frequency signals with a frequency of 4 kHz. The transmission distance of the voice signals is up to 5 km. For G.fast access technology, the frequency is expanded to 106 MHz, the maximum rate can reach 1000 Mbit/s, and the typical distance is shortened to about 100 m.

I hope it will be helpful for you. Thank you!