DSL is a technique used for accessing Internet. ADSL is a type of DSL, which is widely used. This article talks about the differences between them.
Many of us may already know that there is not much difference between DSL and ADSL; the latter is a type of the former. To understand better, one should foremost construe the terms individually.
What is DSL?
DSL (Digital Subscriber Line), also referred as xDSL (x stands for the different techniques used), is a group of technologies that provide high-speed Internet access, by using the ordinary telephone lines. It converts the ordinary telephone line into a high-speed passage for digital audio, video, and data. It is widely used for business and personal purposes. The technology is simple as the setup required for networking already exists. It does not keep the telephone line busy as is the case in the Internet access used in the Dial-up connection. However, the speed depends on the distance between the Internet service provider and the user. More the distance, less will be the speed of the Internet access.
How does DSL work?
POTS (Plain Old Telephone Service) uses copper wired (twisted cable) network, for the exchange of voice information. It uses analog signal transmission and requires a very low bandwidth (0-3400Hz), thus a wide bandwidth remains unused. DSL uses this unused bandwidth to provide Internet service. In this technique, the unused high range of frequency is used for broadband Internet access and the low range is used for voice transmission. In this technique, there is no analog to digital and digital to analog conversion. Digital data is directly fed into the computer using a modem, thus allowing a wider range of bandwidth to be used. Splitters are used to split the low and high frequency signals into two bands. Filters are installed in phones to avoid interference between the range of frequencies used for DSL and telephonic conversion.
Difference between DSL and other Internet Services
| Internet Service | Upstream Speed | Downstream Speed |
| DSL | 128 Kbps to 384 Kbps | 3 Mbps to 6 Mbps |
| Dial Up | 56 Kbps | 56 Kbps |
| Cable | 768 Kbps to 1.5 Mbps | 8 Mbps to 16 Mbps |
| Satellite | 128 Kbps to 256 Kbps | 512 Kbps to 1.5 Mbps |
| Wireless | 128 Kbps to 768 Kbps | 384 Kbps to 2.0 Mbps |
Types of DSL Techniques
There are basically two types –
Asymmetric DSL: ADSL, RADSL, VDSL are types of Asymmetric DSL
Symmetric DSL: SDSL, HDSL, SHDSL are types of Symmetric DSL
In Asymmetric DSL, the bandwidth allotted for upstream and downstream is unequal, whereas in Symmetric DSL, it’s equal. Let us look into the concept of upstream and downstream to understand the broad uses of the technologies.
Downstream: Data transfer from the server to the user is called downstream. For e.g., downloading a song from any website.
Upstream: Data transfer from the user to the server is called upstream. For e.g., uploading an image to a website.
Difference between DSL Techniques
| Type | Upstream Speed | Downstream Speed | Distance Limit |
| ADSL – Asymmetric Digital Subscriber Line | 16 Kbps to 640 Kbps | 1.5 Mbps to 6.1 Mbps | 9,000 feet to 18,000 feet |
| VDSL – Very High Speed Digital Subscriber Line | 1.5 Mbps to 2.3 Mbps | 1.6 Mbps to 52.8 Mbps | 1000 feet to 4500 feet |
| HDSL – High Data Rate Digital Subscriber Line | 1.544 Mbps | 2.048 Mbps | 12,000 feet |
| SDSL – Symmetric Digital Subscriber Line | 1.544 Mbps to 2.048 Mbps | 1.544 Mbps to 2.048 Mbps | 12,000 feet |
| RADSL – Rate Adaptive Digital Subscriber Line | 272 Kbps to 1.088 Mbps | 640 Kbps to 202 Mbps | 9,000 feet to 18,000 feet |
What is ADSL?
ADSL allots more bandwidth for downstream than upstream. The downstream speed (1.5-9 Mbps) is higher than the upstream speed (1.5 Mbps). The downstream speed depends on the distance of the user from the service provider. The speed increases with decrease in the distance. 1.5 Mbps downstream speed can be achieved for 18,000 feet distance; while 9 Mbps speed is possible for distance of 9,000 feet. Most of the Internet users aim for a high downloading speed, as compared to uploading. ADSL is widely used for Internet connections at homes and small businesses. With its use, large unused bandwidth of the copper wired network can be utilized for high speed data transfer. With the help of ADSL, one can talk on the telephone and simultaneously access the Internet. Following are other types of Asymmetric Digital Subscriber Line:
RADSL: The speed of data transfer is adjusted automatically depending on the quality of telephone line and distance from the service provider. The downstream speed is adjusted higher than the upstream speed. RADSL provides a faster speed for premises close to the service provider.
VDSL: It provides a high speed of data transfer for short distance, by connecting to ONU (Optical Network Unit), which is a combination of fiber optic and copper wire networks.
The most important advantage of Digital Subscriber Line technology, is that it uses existing telephonic network for high speed Internet access, without keeping the phone line busy.