Digital Subscriber Line is a networking technology that tenders high speed data transmission over the local loop of the telephone network. Local loop is nothing but a copper wire which is twisted, connecting office, home etc. to the central offices of the telephone company.  The demand for high speed data transfer increases with the escalation of the internet applications. There are various technologies that provide wider bandwidth for data transmission like DSL, Wireless technologies, satellite technologies, CATV etc. These technologies come under the class of residential broadband services. DSL confers telephone service as well as internet service over the same telephone line and facilitates their simultaneous working without any disturbance to the customer. DSL makes use of enhanced copper wire infrastructure to make available efficacious broadband services to customers. In this case wiring upgrade is not necessary but, the equipments at the user end and the company end need to be upgraded. DSL supports transmission of both long-established analog signals and multiple digital signals through the same telephone line. DSL modems use frequency division multiplexing to support analog voice channel, upstream channel and downstream channel. DSL involves point to point connections and are dedicated. No switching is needed. DSL modems are needed at both the user and carrier ends and compatibility between the user equipment and carrier equipment should exist.

DSL always takes advantage of the telephone line and in that, it splits up the frequency into two primary frequency bands such that one will have higher frequency and the other band will have lower frequency. ISP utilizes the high frequency band leaving lower frequency band for voice signals. DSL filter will be installed on each of the phone outlets to filter the high frequency signal and helps user to receive voice signals from the phone.

Sundry versions of DSL are present and in concert termed as xDSL. HDSL (High speed Digital Subscriber Line) is the widespread and primitive one. It transmits data symmetrically at the rate of 1.544 Mbps covering a distance of 3.6 km. It is not preferable for home users, as it requires two lines .HDSL is intended for internet servers, private networks and the telephone company’s own feeder lines. Symmetric DSL (SDSL) is similar to HDSL, here it uses twisted pair cables to provide bidirectional services. In Asymmetric DSL (ADSL) the upload speed is lower than the download speed and hence it is largely used by Internet users, as they prefer more downloads. The upstream speed ranges between 16 Kbps to 768 Kbps and the downstream rate ranges between 1.544 Mbps to 8.448 Mbps. Very high data rate Digital Subscriber Line (VDSL) is in essence an ADSL broadband having higher data rates. The upstream rate ranges from 1.5 Mbps to 2.3 Mbps and having downstream rate to the maximum of 25.82 Mbps. It supports high speed access to data with video, video streaming, data distribution within a building, video conferencing etc. Rate Adaptive DSL (RDSL) is like ADSL including the rate adaptive feature. It will adjust the transmission speed in accordance with the length and quality of the line. When the line is first created, a line polling scheme will be used to fix the connection speed. DSL lite is a technology for rapidly increasing the number of users. The data rate may be lower but it doesn’t require the involvement of Telephone Company to modify the lines. DSL lite equipments are on hand at cut-price.

You can use your phone to attend voice calls even when the internet connection is open. The speed of DSL modem is always more elevated than the regular modem. New wiring is not needed, since the telephone lines are used. Modem will be provided as a part of installation by the company offering DSL service. Some limitations are also present in DSL. The connection operates better, if you are nearer to the central office. The farer location may have weaker signals resulting in satisfactory access speed.