What is DSL?

DSL is a technology for bringing high-bandwidth information to homes and small businesses over ordinary telephone lines. There are numerous different variations of DSL, such as ADSL, HDSL, IDSL, VDSL and RADSL.


DSL stands for Digital Subscriber Line. Digital Subscriber Line technology allows for the transmission of information (voice, video and data), over existing copper telephone lines at incredible speeds. DSL uses your ordinary phone line and you are always connected and for you that means no more waiting for someone in the household to get off the phone. DSL offers users a choice of speeds ranging from 144 Kbps to 1.5Mbps. This is 2.5x to 25x times faster than a standard 56Kbps dial-up modem. DSL technology uses existing 2-wire copper telephone wiring to deliver high-speed data services to homes and businesses. It must be noted that there is a higher SLA (service level agreement) for T1 service or SDSL service which is considered business class service versus ADSL which is considered to be residential class service.

Over any given line, the maximum DSL speed is determined by the distance between the customer site and the Central Office (CO). Most ISP's offer Symmetric DSL (SDSL) data services at speeds that vary from 144 Kbps to 1.54 Mbps, and now even faster up to 6.0 Mbps--so customers can choose the rate that meets their specific needs. At the customer premises, a DSL router or modem connects the DSL line to a local-area network (LAN) or an individual computer. Once installed, the DSL router provides the customer site with continuous connection to the Internet and use of the telephone at the same time.

 

 DSL definitions made easy.
ADSL (Asymmetric Digital Subscriber Line) is quickly becoming the most popular form of xDSL. ADSL supports up to 8 Mbps bandwidth for downloading and up to 1 Mbps for uploading. The asymmetrical nature of ADSL technology makes it ideal for Internet/Intranet surfing, video-on-demand, and remote local area network (LAN) access. Users of ADSL typically download more information than they send.

ADSL requires a voice/data splitter, commonly called a POTS Splitter (Plain Old Telephone Service) to be installed at the consumer's home or business location. The splitter separates voice from data transmissions. For simultaneous use of the telephone and data access, additional phone wires may need to be installed at your location. Full rate ADSL provides service up to a maximum range of 12,000 feet (about 2.0 miles) from the telecommunication provider company's central office to the end-user.

ADSL Lite technology often called Splitterless, G.lite or Universal ADSL and now also known as G.992.2 does not require a POTS splitter to be installed at the consumer's home or business. ADSL Lite provides bandwidth downstream up to 1.5 Mbps and upstream up to 512 kbps. ADSL Lite provides service up to a maximum range of 12,000 feet (about 2.0 miles) from the central office.
 

SDSL (Symmetrical Digital Subscriber Line) delivers high-speed data networking over a single-pair of copper phone lines, at the same speed in both the upstream and downstream directions. Speed ranges from 160 Kbps up to 1.544 Mbps at a maximum range of 15,000 feet (about 2.8 miles). SDSL is ideal for business applications that require identical downstream and upstream speeds such as video conferencing or collaborative computing as well as similar applications appropriate for ADSL technology. SDSL uses the same kind of line-modulation technique employed in ISDN, known as 2B1Q.
 

HDSL (High bit-rate Digital Subscriber Line) delivers high-speed data networking up to 1.544 Mbps over two copper pairs and up to 2.048 Mbps over three pairs at a maximum range of 20,000 feet (about 3.8 miles) from a central office. It is similar to SDSL and has symmetrical transmission capabilities. Most T1 lines installed today utilize this technology.


IDSL (ISDN Digital Subscriber Line) provides symmetric download and upload speeds from 64 to 144 Kbps on a single pair of copper wires. The maximum range of IDSL from a central office is 39,600 feet (about 7.5 miles), but this can be doubled with a mid-span "U" loop repeater. IDSL uses 2B1Q line coding, the same kind of line-modulation technique employed in SDSL, and ISDN.
 

VDSL (Very high bit-rate Digital Subscriber Line) is the fastest xDSL technology, delivering downloads up to 13-52 Mbps and uploads at 1.5 to 2.3 Mbps over a single pair of copper wires. However, VDSL is limited to a maximum range of 1,000 to 4,500 feet (about .2-.9 miles) or 1.6-7.2km from the central office, depending upon the speed.

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