What Is DSL (Digital Subscriber Line) In The Physical Layer ?

In the previous posts , we have seen various wired transmission medium used in the physical layer for data transmission (twisted pair , coaxial cable, and optical fiber). Now we shall proceed further and explore the next important networking device standard used in this layer i.e the DSL technology .

DSL basically stands for the digital subscriber line and it has been developed in order to provide high-speed access to Internet. It allows any user a very high-speed digital communication over the existing local loops. 

Digital subscriber line (DSL) technology is used for high-speed internet communication. DSL technology is further classified as follows :

• ADSL
• VDSL
• HDSL
• SDSL

Thus DSL technology is actually a set of technologies that is referred to ‘ xDSL ‘ where x can be A, V, H or S . The traditional MODEMs cannot provide very high data rates. 

After the traditional modems that have reached their peak data rate, the telephone companies then developed yet another technology, i.e. the DSL  to provide very higher-speed access to the Internet to the users.

What is DSL (DSL Meaning) ? DSL vs Cable

Digital subscriber line (DSL) technology is undoubtedly one of the most promising (technology) for supporting the high-speed digital communication over the existing local loops for the respective users.

DSL technology is a set of technologies, and each differing in their first letter (ADSL, VDSL, HDSL, and SDSL). We will explore each of these in detail in the subsequent posts. 

Now let us see each in brief here :

1. ADSL (Asymmetric DSL ) : Asymmetric digital subscriber line basically provides higher speed in the downstream direction . It implements the FDM technique and uses the 1 MHz capacity of the twisted pair into 3 bands .  

2. VDSL (Very high bit rate DSL) : VDSL is a technique that is used to provide a scheme similar to that of the ADSL  but at a much higher data rate by mainly sacrificing the distance.  It uses the discrete multitone modulation (DMT) technique with a bit rate of 50 to 55 Mbps downstream and 1.5 to 2.5 Mbps upstream . 

3. HDSL (High bit rate DSL) : HDSL was designed as an alternative to the T – 1 line (1.544 Mbps). The T – 1 line basically uses AMI encoding, which is very much susceptible to the attenuation at high frequencies .

It uses full duplex transmission, using echo cancellation with each pair carrying 784 kb/s. The lower bit rate further allows for a lower frequency range of operation that also reduces channel loss and near-end crosstalk. 

4. SDSL (Symmetric DSL) : SDSL is the single twisted pair version of HDSL. It mainly provides symmetric communication. Echo cancellation technique is a signal processing method that normally allows transmission of signals in both directions on a single line simultaneously.

SDSL is generally used by home users and small sized business’ that have an equal need to download and upload data over the Internet. 

Thus, in a nutshell, we can summarize DSL technology as the technology developed by the telephone companies, in order to provide higher-speed access to the Internet. DSL technology is mainly the implementation of various other technologies, each differing in the first letter (ADSL, VDSL, HDSL, and SDSL ).

ADSL further provides a higher speed in the downstream direction than the upstream direction. The high bit rate digital subscriber line (HDSL) has been designed as an alternative to the T-l line (1.544 Mbps).

The symmetric digital subscriber line (SDSL) is one twisted-pair version of HDSL. The very high-bit-rate digital subscriber line (VDSL) is an alternative approach that is very much similar to ADSL .

In the subsequent posts , we will further explore each of the types of DSL in detail . So stay tuned..