Digital Subscriber Line (DSL) Broadband Technology is used to access the wired internet services. DSL internet uses the existing or old copper wire telephone line to provide Broadband connection. It is mainly divided into two categories.
1. Asymmetric Digital Subscriber Line
In this type of Broadband connection, Download Speed will be more than the upload speed. Almost all home users are provided the broadband connection on this technology.
2. Symmetric Digital Subscriber Line
In this type of Broadband connection, Download Speed is equal to upload speed.
How ADSL Technology works
As we already know that Broadband services can be accessed on same old copper wire telephone connection. Three different frequencies are used for Voice and data services. Low frequency (0 t0 4 kHz) is used for Voice service. Middle range frequency (25.875 kHz to 138 kHz) used for upstream Broadband/data connection and High (138 kHz to 1.1MHz) used for Downstream Broadband/data connection.
A splitter is used to separates the low-frequency voice signals and high-frequency data signals. Voice signals are sent to Telephone instruments, and data signals are sent to DSL Modem using different copper wires.
Modem uses two ways to separate high-speed downstream data with comparatively low-speed upstream data
- Frequency Division Multiplexing (EDM): In this technique, frequency bands are divided in Downstream and upstream frequencies. The downstream frequency band is further time multiplexed or separated in time to get higher speed in downstream.
- Echo Cancellation: Here upstream and downstream signals are separated by echo cancellation method. This technique is mostly used in conventional modems.
Modulation used in ADSL Modem
- Carrierless Amplitude Phase Modulation
- Discrete Multitone Modulation
DSL speed depends on upon following factors
- Its distance from Digital Subscriber Line Access multiplex or Telephone Exchange
- Number of Joints in Copper Wire throughout the length
- Quality and Thickness of Copper wire
More DSL Technologies
High Data Rate Digital Subscriber Line
It requires two pairs of copper wires one is for upstream and another for downstream. Speeds of upstream and downstream data are same. Maximum offered speed is 2Mbps and maximum distance from telephone exchange can be 4.57kms.
Symmetrical Digital Subscriber Line
It’s very much similar to High Data Rate Digital Subscriber Line but works on one pair of Copper wire. Maximum upstream and downstream speeds are 2Mbps.
Rate Adaptive (RADSL)
In this technology, modem senses the quality of copper wire with the help of software and accordingly it adjusts the upstream and downstream speed.
Very High Speed (VDSL)
This technology offers the highest bandwidth in downstream. Its range is 1.37kms with a downstream speed of 12.96Mbps. It can provide 51.96Mbps speed up to 0.3kms range. Upstream speed is 1.6 to 2.3Mbps.
Advantages of Asymmetric Digital Subscriber Line
High-speed internet connection
Always on internet connection
Video on Demand, Games on Demand, IPTV services can be provided
All above services along with internet facility can be accessed on the same old copper telephone wire.