What Are the Different Types of DSL Technology?

Black Lan cable with rj45 plug isolated
Chad Baker/Getty Images

Question: What Are the Different Types of DSL Technology?

All types of DSL Internet service can be categorized as either asymmetric or symmetric.


Asymmetric DSL

Asymmetric types of DSL connections provide more network bandwidth for downloading (from the Internet service provider down 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.

Asymmetric DSL technology is popular in residential DSL services as home Internet users predominately use downstream bandwidth. Typical asymmetric DSL services support 5 Mbps for downloads and 1 Mbps for uploads.

Common forms of asymmetric DSL include:

  • ADSL (and G.Lite)
  • VDSL

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. Typical symmetric DSL connections support 1.5 Mbps for downloads and uploads.

Common forms of symmetric DSL include:

  • SDSL (and G.Lite)
  • HSDL -┬ádeveloped in the early 1990s, making it one of the oldest forms of DSL. HDSL offered data rates up to 2,048 Kbps but required multiple phone lines, making it eventually obsolete.

Other Types of DSL

IDSL is a hybrid DSL / ISDN technology developed along with other types of DSL but rarely used nowadays due to the relatively low speeds (128 Kbps maximum data rate) it supports.