Difference Between ADSL and SDSL (With Table) 

A good internet connection is always necessary whenever we upload or download any software, movies, or applications. Internet speeds vary due to several reasons, and there may be vast differences between upload speed and download speeds. The majority of people require good download speeds over the upload speeds. But this is not the same for every person. ADSL and SDSL are two important terms when it comes to Broadband internet connections.


The main difference between ADSL and SDl is that ADSL is Asymmetric digital subscriber line, whereas SDSL stands for Symmetric digital subscriber line. The bandwidth is what primarily distinguishes these two terms from each other. As the name suggests, SDSL is symmetric in its work; it provides equal upload and download speeds. ADSL can also produce good download speed but at times fails to produce good upload speeds. Also, ADSL can have a telephone unit on the same line, while it is not possible in the case of SDSL.

An ADSL provides good download speeds on a broadband internet connection. But comparatively, the upload speeds remain significantly low. People who upload a lot of content may prefer SDSL over ADSL. However, the upload speed provided by ADSL may not be a headache to people uploading light content with less data consumption. A major plus point for ADSL is that it can have a telephone unit and DSL on the same two wires. It could be used simultaneously.

In the case of SDSL, the upload and download speeds are symmetric. It is used to transmit digital data with the help of copper wires. An SDSL generally utilizes the whole bandwidth. This keeps no room for a telephonic unit. It proves to be a drawback in the case of SDSL. The positive point lies here with equal speeds in upload and downloads, which vary in the case of ADSL. In general, equal bandwidth is given to both upload and downloads in the case of SDSL.

Comparison Table Between ADSL and SDSL

Internet speedsUpload and download speeds are differentUpload and download speeds are similar
 Telephone unitCan support a telephonic unit on the same lineDoes not support telephonic unit on the same line
Type of technology StandardizedProprietary 
AdaptationCurrent technology(used today)Legacy technology 

What is ADSL?

ADSL stands for Asymmetric digital subscriber line. In this type of internet broadband connection, the upload and download speeds vary. The download speeds are always at a higher place than the upload ones. 

It can have high transmission rates and can be used over normal copper telephone wires. This technology is called standardized technology and is used today, giving it a tag of the current technology. 

It is primarily utilized to obtain content from the internet, that is, by downloading them but serving content accessed by others on the internet. Generally, the ADSL systems are installed at a very short distance from telephone exchanges.ADSL provides continuous always available on broadband connections.

To get access to an ADSL system, a DSL modem is primarily installed where the customer wants it. In addition, the installed modem transfers digital data over the local loop of a telephone network. Then a network gets established between the installed modem and the source of the telephone company. 

It operates in a loop of telephone network that connects the telephone company office with the customer’s location. The telephone company uses a DSLAM system to provide its service to multiple ADSL users.ADSL networks are generally full-duplex.ADSL drives a lot of internet connections globally in today’s date.

What is SDSL?

SDSL stands for Symmetric digital subscriber line. As the name suggests, the connection in the case of SDSL is symmetric in working. This means that the upload and download speeds provided by SDSL connections will be equal. DSL transmits digital data through copper wires. 

In the case of SDSL, the bandwidth in the downstream direction from the network provider to a subscriber is equal or symmetric to the bandwidth in the upstream direction from a subscriber to the network.

SDSL is said to be a legacy technology as it was never developed so much. It was founded as a proprietary system, but the standardization procedure never actually took place properly. This brings about certain restrictions in the usage of the SDSL system.

Generally, SDSL is used in situations where data flow in both directions needs to be proper and fast. In situations where a lot of information is getting downloaded and uploaded simultaneously, here SDSL plays a vital role. Due to this, SDSL can improve the quality of VoIP calls better than ADSL connections. 

In the case of SDSL, also distance plays a role in maintaining network speeds properly. Yet, due to lack of standardization, this technology is used less than the ADSL technology in today’s world. It is still considered a proprietary technology that does not support a telephone unit over the same line.

The Main Difference Between ADSL and SDSL

  1. ADSL has asymmetric or unequal broadband speeds in uploading and downloading, whereas the speed remains equal in the case of SDSL.
  2. ADSL is a Standardized technology, whereas SDSL is Proprietary in nature.
  3. ADSL technology is used today, while the SDSL technology is considered as legacy and is in use much lesser than ADSL.
  4. ADSL systems can support a telephone unit on the same line, while it is not possible in the case of SDSL.
  5. The upload speed is comparatively lesser in the case of an ADSL than that of SDSL, yet it does the job.


The internet speeds may vary from place to place depending upon several factors. One must keep in mind where their priority lies. An ADSL can do the job if the uploading content isn’t that huge while the downloading speeds are perfect. It is essential for connecting and managing the telephone of customers from telephone offices. 

SDSL still needs standardization, without which it stays as the technology of legacy and proprietary. Selecting the proper broadband connection lies within your hands. Keeping in mind the drawbacks and advantages, choose the correct technology for yourself. In Broadband internet connections these are important factors to be considered. 


  1. https://journals.sagepub.com/doi/abs/10.1177/108471380500900402
  2. https://www.tandfonline.com/doi/abs/10.3109/14992027.2012.705903