What is DSL?
DSL, Digital Subscriber Line technology is a new way to utilize your existing copper telephone lines (like the ones in your house or business) and deliver very high speed connections. It works like your existing, slow dial-up modem but without the slow dial-up part. With DSL you are always connected directly to the Internet (or Corporate Intranet) with your own secure, dedicated line.

This is accomplished by multiplexing your telephone line into 3 separate bandwidths or frequencies. Currently your voice is carried over the lower frequencies (30hz to 4khz) leaving the higher frequencies or bandwidth unused. DSL technology has enabled us to utilize the higher frequencies for two way data transmission at very high speeds. This way we can use the 300khz to 700khz band for upstream transmission and 1000khz and above for wide frequency, very high speed downstream service. And since we are using the bandwidth your current phone doesn't, you can talk on your phone and surf the net at the same time With DSL you don't need to add an additional phone line! 

Also by separating your voice and data into discrete channels, we can transfer the data portion over new, optimized packet or cell switched connections. This is far superior and faster than using existing, congested "legacy" phone networks built 50 years ago for voice transmission (or telegraph) only. 

Your DSL service works by sending (via your new digital modem, also called a router) your requests to the local telephone facility or Central Office. At that point you are placed on our Fiber Optic Network (Frame Relay and ATM) and directed to our facility. 

We in turn, verify your access and pipe you into the Internet via our multiple and redundant OC24's and DS3's (very large pipes). Your web pages or Corporate documents are returned to you in the reverse order. Using a National Fiber Optic Network allows us to offer this service anywhere in North America that has DSL activation in the local Central Office. 

DSL Types
ADSL (Asymmetrical Digital Subscriber Line)
ADSL was originally designed by telephone companies to provide video-on-demand to compete with the cable industry. Turns out this asymmetrical approach is also perfect for surfing the web. ADSL is faster in the return (download) than send (upstream) direction. As a typical use on the net is to send a small request and receive a large file or download, this approach is excellent. Upstream speeds are usually 128kbps to 1.088Mbps while downstream speeds race up to 8.192Mps (over 5 times as fast as a T1 circuit). 
HDSL (High bit rate Digital Subscriber Line)

HDSL was developed as a faster cousin to ISDN (64-128kbps) technology. This enabled telephone companies to offer T1 (1.544Mbps) speeds over regular copper phone wire without the use of repeaters. HDSL is the oldest and most heavily deployed version of DSL. If you currently have a T1 circuit on two pairs of copper wires, you are probably already using DSL! 
RADSL (Rate Adaptive Asymmetrical Digital Subscriber Line)

RADSL is basically a rate adaptive version of ADSL. Rate adaptive technology allows a service provider to adjust the bandwidth for a particular application or compensate for line length or quality. This adjustment can be pre configured or self adjusting. A larger percentage of users near a Central Office can be served by RADSL's ability to lower data rates to extend the reach of the service. Like ADSL, it also operates on standard phone lines. 
SDSL (Symmetrical Digital Subscriber Line)

SDSL is the symmetrical cousin in the DSL family. It was designed for applications requiring high bandwidth in both directions. Typical current speeds are 144kbps to 1.1Mbps in both directions. This is well suited toward large file transfers toward and away from users or for Web Site Hosting services. 
VDSL (Very high bit Digital Subscriber Line)

VDSL is a shorter distance, higher speed derivative of the DSL family. It was intended for "the last mile", the costliest link from any service to any final destination. As this last segment is usually dedicated to a single customer, VDSL can be combined with fiber to offer cost effective, short distance runs at speeds of up to 52Mbps.
DSL vs. Cable
Cable modems are the cable companies answer to high speed data access. This technology was developed to provide video-on-demand or other high bandwidth services. The technology is sound but has quite a few inherent problems with the approach. 

1. Service: A local loop of fiber cable must be available near all residences (this is not for business users) to use this service. The problem is the very small percentage of currently wired users (usually newer buildings or developments). This dictates that the cable companies must run inordinate amounts of new fiber that is very expensive to install and very time consuming. The cost to rewire the US with fiber is estimated at $400 billion and would require about 30 years to implement.
2. Speed: The cable users are set up as a LAN or Local Area Network to share a single fiber connection among the hundreds (maybe even thousands) of subscribers. As more and more of your neighbors connect and surf the Web, your bandwidth or line speed diminishes proportionately.
3. Security: Being on a Local Area Network does not provide for a secure connection for electronic commerce. Your connected neighbors will be able to intercept your credit card or other sensitive, confidential company data at will.
So if availability of service, speed or security are not concerns of yours, this service may work well for you. If you prefer a widely available system (works on your existing phone line), Guaranteed, Direct, High Speed Access that is Secure, DSL is your answer. Compare for yourself below:

Type High Speed? Secure?
Cable Maybe - depends on number of users online No - shared network
DSL Yes - up to 1.5megs Yes

Type Low Cost? Use an existing phone line?
Cable Yes No - requires new cable installation and expense
DSL Yes Yes

Type Time to download a 100meg file
Cable Varies depending on number of users
DSL 66 seconds

DSL is actually a higher speed version of ISDN which itself is an improved, higher speed version of older, analog dial-up modems. ISDN stands for Integrated Services Digital Network or the ability to combine voice and data on the same line. Unfortunately due to lack of any uniform standards or mass deployment to make it cost effective, ISDN never really caught fire. Between the additional phone lines and marginal gain in speed over a 56kbps modem, most users felt that it wasn't worth the hassle. ISDN offers dedicated, always on access but comes with an additional bill for minutes used. ISDN is secure for e-commerce transactions, but at 64k it is painfully slow.
DSL Glossary
10BASE-T The Institute of Electrical and Electronic Engineers (IEEE) specification for Ethernet over unshielded twisted pair cable. 

ADSL Asymmetric Digital Subscriber Line. High speed technology utilizing existing phone lines to transmit data. Typical speeds are from 144Kbps to over 8Mbps currently. See DSL Types for more info.

ATM Asynchronous Transfer Mode. High Bandwidth packet technology that uses 53 byte fixed sized cells to deliver data, voice and video. 

ATU ADSL Transceiver Unit. Equipment used for DSL technology. In the Central Office it is called ATU-C (central) and in the Customer locations it is called ATU-R (remote). See our home page for diagram.

Backbone A central very high speed fiber network that is used to connect smaller, independent networks. 

Bandwidth A term used to describe the number of bits that can move across a communications system in a given amount of time. 

BPS Bits per second. The number of bits passing a point every second. The rate of transmission for digital signals. 

Broadband Data transmissions of voice, data and video signals over a single medium at high speeds. 

Cable Modem Modem designed for use with coaxial cable circuit. 

Campus Network A local network between floors of a building or between buildings of close proximity. Usually runs are short distance and without public access. 

CAP Carrierless Amplitude Phase Modulation. A two dimensional line code used in ADSL. 

CLEC Competitive Local Exchange Carrier. The new competitors to the original Bells after deregulation. See also ILEC. 

CO Central Office. The building used by telephone companies to connect local users to their infrastructure. 

Concentrator Electronic device used to aggregate several channels or sources into one stream for transmission over one line or link. Opposite of Multiplexer. 

CPE Customer Premises Equipment. Terminating equipment supplied by carrier for use at customer site ie. modems, phones, routers.

DACS Digital Access & Cross-Connect System. A digital cross-connect device used to route lines to multiple ports. 

Dedicated Circuits Telecommunications lines reserved along predetermined routes for specific customers usually in a point to point configuration.

DNS Domain Name Services. Name (actually numbers) used by servers for identification in a local or global network 

Downstream The direction of data returned from the Central Office back toward the user. Usually used with transmission speed (ie. 1.5Mbps downstream)

DSL Digital Subscriber Line. Technology that combines two way voice and data transmissions at very high speeds over normal phone lines. See DSL Types for more info. 

DSLAM Digital Subscriber Line Access Multiplexer. Equipment used in the Central Office or Intranet to concentrate local users onto a fiber Backbone 

DSP Digital Service Provider. New breed of Internet Service Providers who specialize in direct, digital Internet connections like Flashcom

DSU Digital Service Unit. Digital device at customer premises to facilitate xDSL service. Also known as a Modem or Router. 

E1 The European equivalent of our T1 that operates at 2.048Mbps.

E-Commerce Electronic Commerce. Electronic transactions between business and customers via the Internet. These are typically private and secure. 

Ethernet Term used to describe a baseband LAN specification originally designed by Xerox. IEEE 802.3 describes the current standards for this protocol. 

Firewall A secure gateway or virtual wall between two different computer networks that will prevent unauthorized use or access. 

Fractional T1 A portion of a T1 circuit that has been divided into 24 separate 64Kbps channels. Actual size is a multiple of 64. 

Frame Relay A data communication technology based on packet switching of variable length frames that are protocol independent. 

FTP File Transfer Protocol. Method for accessing and transfer of files to or from an Internet Server or Workstation. 

Gbps Giga bits per second. 1,000,000,000 (one billion) bits per second, a measure of telecommunications speed. A thousand Megabits. 

HDSL High bit rate Digital Subscriber Line. See DSL Types for full definition. 

HTU HDSL Transceiver Unit. Electronic device used for the sending and receiving of HDSL transmissions. At the CO side it is called HTU-C (central office) and on the user side it is called HTU-R (remote). 

IDSL Integrated Digital Subscriber Line. An ISDN based version of DSL using 2BIQ line code. 

ILEC Incumbent Local Exchange Carrier. All the original Bells are called ILEC's after the Telecommunications Act deregulation. All new competitors are known as CLEC's 

Internet Global network of interconnected commercial, governmental and educational computers using TCP/IP as a communications protocol.

InterNIC Co-op between National Science Foundation and Network Solutions for registration and tracking of Internet domain names. 

Intranet A private network that uses Internet software and standards.

IP Internet Protocol. A software standard that controls the flow and routing of content between Internet devices or machines. 

ISDN Integrated Services Digital Network. Public circuit switched network that combines voice and data into a single medium. Usually runs at 64K or 128K, predecessor to DSL technology. 

ISP Internet Service Provider. Company that provides connection to the Internet typically via a dialup link (ie. AOL, Always Over Loaded) . See DSP for a better definition of service. 

IXC Inter Exchange Carrier. All telecommunications companies who provide long distance service, aka Common Carriers. 

Kbps Kilo Bits Per Second. A measure of time relating to telecommunications speeds. One kilobit is 1,000 bits of information, the higher the number the faster the transmission speed. 

LAN Local Area Network. A data communications networks of computers, printers, file servers, etc.. in a local environment. 

LEC Local Exchange Carrier. Provider of local telecommunications services. See also CLEC, ILEC 

Local Loop Also called the "last mile". The length of telephone wire from the local Central Office to it's final termination at customer premises. Usually about 1-3 miles or less. 

Mbps Mega Bits Per Second. Like Kbps a measure of transmission rates. One Megabit equals 1,000 kilobits. 1.5Mbps DSL is a heck of a lot faster than your current analog service. 

Modem An antique electronic device that was used to modulate or change your computers digital output to an analog form for transmission over separate, dedicated phone lines. The old school of data transmission.

Multiplexer An electronic device that allows one source to be split into multiple channels. The opposite of a concentrator. 

NAP Network Access Provider. Service or company that provides actual entry into the Internet backbone. Also called a DSP or Flashcom.

NIC Network Interface Card. The hardware that handles the protocol conversion between your computer and a connected network. Used in DSL service to talk to router. 

NSP Network Service Provider. Company who provides connection to networks or Internet. Also called ISP, DSP, ILEC, CLEC or Flashcom.

NTU Network Termination Unit. Equipment to facilitate DSL network access at customer premises. Also called a router. 

POP Point of Presence. Location at which to gain access to a public or private network. 

POTS Plain Old Telephone Service. As it sounds, your basic telephone service. 

Protocol A format or rules two or more computers must follow in order to communicate. 

RADSL Rate Adaptive DSL. See DSL Types for more info. 

RBOC Regional Bell Operating Companies. The five companies created after the breakup of AT?, Bell Atlantic, Bell South, Ameritech, Southwestern Bell and US West. 

Repeater Electronic device used to regenerate and enhance signal quality over long cable distances. 

Router Electronic device that transmits and receives data packets in a network. 

SDSL Symmetrical Digital Subscriber Line. See DSL Types for more info.

SMDS Switched Multimegabit Data Service. A public packet switching service used by telephone companies in major metropolitan areas.

SONET Synchronous Optical Network. A network standard that uses fiber optics to transmit data at gigabit level bandwidth. 

T1 Digital transmission at 1.544Mbps. T1 is the most common transmission technique used in North America. 

T3 Digital transmission at 45Mbps. Basically 30 T1 circuits. 

TCP/IP Transmission Control Protocol/Internet Protocol. Open communication protocol that allows computers with different operating systems to communicate with each other on the Internet. 

Twisted Pair Cable of two 18 to 24 gauge solid copper strands twisted around each other. The twisting helps protect against electromagnetism and Radio Frequency Interference (RFI). 

Upstream Refers to transmission speed from user to the Internet. Opposite of Downstream. 

VDSL Very high bit rate Digital Subscriber Line. See DSL Types for more info. 

VPN Virtual Private Network. A network service that is provided over a public network that is secure and works like a private network.

WAN Wide Area Network. A network with devices over a wide geographical area. 

xDSL Refers to all variations of the DSL family or technologies.