Difference Between ADSL and SDSL (With Table)

Both ADSL and SDSL (also known as asymmetrical digital subscriber lines) are technologies that allow internet access by using your existing phone line. SDSL is faster and more reliable, but ADSL is cheaper to set up, and the maximum download speed on ADSL is often higher.

ADSL works by sending data down the telephone line in chunks of 128 kilobits per second (kbps). SDSL sends data in a series of pulses that are much shorter than those used by ADSL.


The main difference between ADSL and SDSL is that ADSL uses two lines to provide a DSL and a telephone connection. However, SDSL does not include a phone line. ADSL stands for Asymmetric Digital Subscriber Line. On the other hand, SDSL is an abbreviation for Symmetric Subscriber Digital Subscriber Line.

Difference Between ADSL and SDSL

The benefits of getting an ADSSL connection include increased online activity and the ability to download movies faster than ever before. Accessing more bandwidth quickly means smoother online games, videos and music downloads without lagging or buffering. ADSL allows a user to download data at up to 24 Mbps and upload it at 1 Mbps. This is enough speed for users to stream videos online or watch high definition movies.

SDSL is a newer form of DSL developed to give users more bandwidth and higher speeds than standard DSL service. Up to 300 Mbit/s (megabits per second) are available. SDSL service delivers faster download speeds and allows multiple users to share a single DSL line. This makes it an attractive choice for companies with large amounts of data to transmit.

Comparison Table Between ADSL and SDSL

Parameters of Comparison ADSL SDSL 
The type of linkThe Asymmetric Digital Subscriber Line (ADSL) is asymmetric.SDSL is symmetric.
Set of telephonesA telephone unit can be connected to an ADSL line.A telephone device cannot be connected to an SDSL line.
Type of technology ADSL (Asymmetric Digital Subscriber Line) is a standardised technology.The SDSL language was never standardised.
CostADSL is a low-cost option.SDSL is an expensive service.
Possibility of useADSL It’s quite likely that you’ll use it.SDSL is unlikely to be used.
Form in its entiretyAsymmetric Digital Subscriber Line is the full name of ADSL.SDSL stands for Symmetric Subscriber Digital Subscriber Line in its full form.
Launched inAround the year 1998, ADSL was introduced.SDSL was first introduced in 2001.

What is ADSL?

ADSL is a technology that allows high-speed video and voice transmission to households over standard copper telephone lines. It works over the existing phone lines and can be used with either a fixed or mobile ADSL modem.

ADSL is available through your broadband provider, which probably means you pay an extra monthly charge for it, but it’s worth it. The benefits of ADSL are numerous:

· Faster speeds. By default, your computer downloads data at about 20 megabits per second (Mbps). But when you’re connected to the Internet via ADSL, you get a maximum of 40 Mbps. That’s roughly 1,000 times faster than dial-up Internet access.*

· Multiple devices on one line. You can connect multiple computers or modems to your router via an Ethernet cable, allowing you to share the connection among your other devices — such as your television, game system and laptop — without having to go through a separate Internet service provider (ISP).

· No setup headaches. Getting started with ADSL is very simple if you have an existing broadband connection.* There’s no additional software to download or configure; all of the work is done automatically in the background by your broadband provider.

What is SDSL?

SDSL is a digital subscriber line that transmits data over copper telephone lines. SDSL uses the same bandwidth as ADSL, but instead of sending the data in one direction, a device on the receiving end of an SDSL connection sends it in both directions. The primary benefit of SDSL is its ability to send larger data volumes than ADSL and its higher speed over copper telephone lines. 

SDSL offers many benefits over standard DSLs, such as:

Low latency: SDSL is designed with low latency in mind. Compared to traditional DSL, where the delay in transmitting data can be as much as 30ms, SDSL’s latency is only around 2ms. This means you will see less lag time when using your Internet connection and will be able to stream multimedia files or play online games without any interruptions.

High availability: The number of active connections on an SDSL network is limited compared with conventional DSL. On an ADSL2+ network, up to 25 connections are allowed, whereas, on an SDSL1 network, there is a limit of 16 connections. With this limitation, you’ll be able to access the Internet whilst sharing your connection with other users simultaneously.

High bandwidth: Depending on the type of modem used for your connection, SDSL provides very high bandwidth, which means it can provide most data that can be sent through an internet connection in a very quick given length of time.

Main Differences Between ADSL and SDSL 

  1. The upload and download speeds of an ADSL connection are not equal. On the other hand, SDSL offers the same download and upload speeds.
  2. SDSL is a costly service, whereas ADSL is a low-cost choice.
  3. You’re more than likely to utilise ADSL, but SDSL is unlikely to be used.
  4. ADSL was initially deployed in 1998, while SDSL was first provided in 2001.
  5. SDSL is symmetric, but ADSL is asymmetric.
  6. An ADSL line can be used to connect a telephone unit; however, an SDSL line cannot be used to connect a telephone device.
  7. The SDSL language was never standardised, but ADSL (Asymmetric Digital Subscriber Line) is a standardised technology.


The main difference between ADSL and SDSL is the frequency used by ADSL. ADSL is a technology that allows high-speed internet access to be sent through standard telephone lines. It has higher bandwidth than SDSL but is slower, meaning that it’s more expensive and requires more equipment.

On the other hand, SDSL is a faster version of ADSL that fibre-optic broadband providers often use because it’s faster and can be implemented using existing infrastructure.


  1. https://rupress.org/jcb/article-abstract/170/6/983/51960
  2. https://www.sciencedirect.com/science/article/pii/S0009898106003895