What Are the Different Types of DSL Technology?

All DLS Technology Is Either Asymmetric or Symmetric

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DSL (Digital Subscriber Line) high-speed internet service for homes and businesses competes in many areas of the country with cable and other types of broadband internet services. DSL delivers a broadband network using a copper phone line. Most types of DSL service are asymmetric. All types of DSL internet service can be categorized as either asymmetric or symmetric. The service that is best for you depends on whether you do a lot of streaming or require support for simultaneous voice and video communications.

Asymmetric DSL

Asymmetric types of DSL connections provide more network bandwidth for downloading from the internet service provider to the subscriber's computer than for uploading in the other direction. By reducing the amount of bandwidth available upstream, service providers are able to offer relatively more bandwidth downstream, which reflects the typical subscriber's needs.

Asymmetric DSL technology is popular residential DSL service where home internet users predominately use downstream bandwidth. 

Common forms of asymmetric DSL include the following:

  • ADSL (Asymmetrical Digital Subscriber Line) has a downstream rate of up to 8 Mbps and an upstream rate of 384 Kbps. It supports telephone service and data transmission at the same time.
  • ADSL 2+ is a newer version of ADSL that delivers download speeds of up to 20 Mbps and upload speeds of up to 850 Kbps.
  • ADSL Lite or G.Lite is a version of ADSL that offers slower speeds of up to 1 Mbps downstream speed and 512 Kbps upload speed.
  • R-ADSL (Rate-Adaptive Digital Subscriber Line) delivers the same transmission rates as ADSL, but the transmission speed can be adjusted by the modem.
  • VDSL (Very High Bit-Rate Digital Subscriber Line) is the fastest DSL service. It offers downstream rates of up to 52 Mbps and upstream rates of up to 2.3 Mbps over a single copper wire. 

Symmetric DSL

Symmetric types of DSL connections provide equal bandwidth for both uploads and downloads. Symmetric DSL technology is popular for business-class DSL services as companies often have greater needs for transferring data. It is also the technology of choice for simultaneous voice and video communications, which require a high speed in both directions for effective communications.

Forms of symmetric DSL include:

  • SDSL (Symmetric Digital Subscriber Line) offers equal upstream and downstream transmission speeds of up to 1.54 Mbps.
  • SHDSL (Symmetrical High-Speed Digital Subscriber Line) is the same technology as SDSL, but the two standards were approved separately. SHDSL was approved by the International Telecommunications Union, and SDSL was approved by the European Telecommunications Standards Institute.
  • HSDL (High Bit-Rate Digital Subscriber Line) was developed in the early 1990s, making it one of the oldest forms of symmetric DSL. HDSL offered data rates up to 2.048 Mbps but required multiple phone lines, which eventually made it obsolete.

Other Types of DSL

IDSL (ISDN Digital Subscriber Line) is hybrid DSL/ISDN technology. It was developed along with other types of DSL but is rarely used nowadays due to the relatively low speeds (144 Kbps maximum data rate) it supports. IDSL offers an always-on connection, unlike ISDN.