The A in ADSL means asymmetric DSL. This recognizes that for home use, since people tend to be more of a consumer of data than a producer, a slower upstream (upload) speed can traded off for a faster downstream (download) speed. In addition, the ADSL standard allows for regular phone service to be squeezed into the low end of the frequency spectrum. ADSL therefore needs a splitter to be placed during installation.

A cable modem is a box that uses the coax cable your cable company uses for TV signals, to transmit data. Since cable TV was designed as a broadcast system, the cable is shared amongst many people in a small area, and only recently have cable company equipment started offering data upload, many cable modems require you also have a good old modem for the path back to the internet...

DSL is the next generation of internet access technology. A house or business with DSL has a data socket, that looks like a phone socket. DSL is a direct connection to the internet, always on.

To connect, a "DSL modem" is needed (ATU-R); DSL modems are starting to be available on the open market, but they are normally supplied by the DSL provider you choose, since DSL standards are varied, and the modem must be compatible with the equipment favored by the provider. (When talking to your provider, you may ask if they allow you to source your own equipment, for example, second-hand).

DSL modems are of three basic types: external, internal or USB. For external modems, on the back is a socket, usually marked LAN. A cable (ethernet cable) connects this to your computer, which needs an ethernet card, (known as a Network Interface Card, or NIC), such cards are available from dozens of vendors at prices as low as $20, and for this purpose, they all work the same way and are all compatible.

Many current computers, such as the iMac, come with a NIC, and socket, built-in, simplifying things still further. Unlike advanced graphics boards or other specialized hardware, even the oldest computer can accept a NIC card, as long as it has a spare slot. For internal DSL modems, or USB modems, the equipment is plugged in, and some driver software must be loaded into your computer before it can be used.

Unlike ADSL and SDSL, High Bit Rate Digital Subscriber Line (HDSL) is a symmetric method of transmitting data at speed rates up to 1.5 Mbps in both directions. Because of the symmetric properties, the highest transmission rates can only be supported at lengths of 15,000 foot distances of two or more twisted pair lines. HDSL is an ideal service for campus environments and digital local loops, because of these distance requirements. High-Pass Filter (HPF) A signal filter which would be installed in a customer premises ADSL modem (ATU-R), which only allow higher frequency data to be delivered to the modem. See Low-Pass Filter. Hub The hub is a critical network element that connects everything to one centralized point. A hub is simply a box with multiple ports for network connections. Each device on the network is attached to the hub via an Ethernet cable.
source: aware.com

IDSL is DSL at 144 kbps. IDSL uses ISDN transmission coding, bundling together both ISDN channels and voice all on one circuit. IDSL does not use any kind of dial up nor involve per-call fees. For those that live too far for regular DSL, IDSL may be the only DSL option. IDSL tends to be priced at a rather higher rate per bit of speed, than any regular DSL. IDSL can still be a very satisfactory solution for data transmission compared to the alternatives (modem), coping very well with online gaming, and medium quality streaming audio/video.

ISDN is Integrated Services Digital Network - Gives a user up to 56 kbps of data bandwidth on a phone line that is also used for voice, or up to 128 kbps if the line is only used for data.

Abbreviated DSS, a network of satellites that broadcast digital data. An example of a DSS is DirecTV, which broadcasts digital television signals. DSS's are expected to become more important as the TV and computer converge into a single medium for information and entertainment.

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The S in SDSL stands for Single line DSL. SDSL needs just one twisted pair (line), whereas some other earlier DSL standards needed two, or even three pairs. In addition, it is useful to remember that this standard is symmetric, ie, the maximum data rate both upstream and downstream is the same. Compare this to ADSL (which also needs just one line!).

A T1 line is a dedicated phone connection supporting data rates of 1.544 Mbits per second. A T-1 line actually consists of 24 individual channels, each of these channels supports 64 Kbits per second. Each 64Kbit per second channel can be configured to carry data or voice transmissions. Many telephone companies will allow you to buy just some of these individual channels, known as fractional T-1 access. T-1 lines are a popular leased line option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone. The Internet backbone itself consists of faster T-3 line connections. A T1 line is also a great solution for business that have more than 20 employees using the internet or businesses that utilize significant voice and data applications.

T1 lines are sometimes referred to as DS1 lines.

T1 is a term for a digital carrier facility used to transmit DS-1 formatted digital signals at 1.544 Megabits per second. A fractional T1 would be any data transmission rate between 56/64 Kbps and 1.544 Mbps. Fractional T1 lines are less expensive but have a fraction of the 24-channel capacity of a regular T1 line. For companies whom a T1 line is not necessary, fractional T1's are available and at a lower cost. They simply use a fraction of the total channels available for a full high-speed internet T1line.

A T-3 is high-speed line, powered by DS3 Technology, capable of delivering 44.7 Mbps (44,700K) in both directions. For many years, the fastest, and unfortunately, the most expensive way to connect to the outside world was through a ds1 or T1 connection. DS stands for Digital Signal or Digital Service. Now more commonly used and not near as expensive as it used to be, DS3 or Data Service Level 3 is the connection of choice for many large companies and places that require a lot of bandwidth. DS3 technology is used for T3 lines and allows connections to the Internet to reach speeds of up to 44.736 megabits per second.

A large company needs something more than a T1 line and could probably use a T-3 line powered by DS3 technology. The following table shows some of the common line designations:

DS0 - 64 kilobits per second

ISDN - Two DS0 lines plus signaling (16 kilobits per second), or 128 kilobits per second

T1 - 1.544 megabits per second (24 DS0 lines)

T3 - 43.232 megabits per second (28 T1s)

OC3 - 155 megabits per second (84 T1s)

OC12 - 622 megabits per second (4 OC3s)

OC48 - 2.5 gigabits per seconds (4 OC12s)

OC192 - 9.6 gigabits per second (4 OC48s)

T-3 lines are used mainly by Internet Service Providers (ISPs) and large companies connecting to the Internet backbone and for the backbone itself.

A T3 connection is a point-to-point dedicated line that provides 672 64-Kbps voice or data channels or in other words 28 T1 lines. A T3 is used to transmit digital signals at 44.736 megabits per second and has enough bandwidth to transmit full-motion real-time video, and very large databases over a busy network. A T3 line would be installed as a major networking channel for a large corporation or university with high volume network traffic.

When you need more capacity, you often have to buy it in the next available increment, which may end up costing more than you want or can afford to spend. Worse yet, with current, "bursty" application requirements, the need for additional bandwidth can often be as temporary as it is critical. By providing flexible capacity, or "bandwidth on demand," service providers can help customers deal with variations in traffic, and with avoiding a high fixed monthly payment. True bandwidth-on-demand services should allow for a wide range in capacity.

Although anybody can purchase a burstable T3, this type of connection can be costly, even as costly as a full 45Mbps connections. Burstable lines can be found at their lowest cost at a colocation facility. At a colocation facility, or "colo", many users share a large OC3 or OC12 pipe. As a customer you will not have to pay for a the fixed cost of such a large pipe, but will have the benefit of being able to burst up to very high speeds if necessary. If you need the reliability of a large pipe fur busty traffic but don't have the capital consider a colo. If you have a steady volume and are consistent, you may consider keeping services in house and going with a T3 connection. Whether you're considering a colocation facility or a T3 to the door, make sure you use a broker to help guide you through the providers and plans available.

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