Glossary, Device, Downstream, Firmware, Dmt

Glossary

ADSL

Short for Asymmetric Digital Subscriber Line, a technology that allows more data to be sent over existing copper telephone lines (POTS). ADSL support data rates of fromm 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).

ATM

Short for Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.

Device

Any machine or component that attaches to a computer. Examples of devices include disk drives, printers, mice, and modems.

DHCP

Short for Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. Many ISP's use dynamic IP addressing for dial-up users.

Downstream

The direction of a downstream signal is from the ISP/service provider to the user's computer (downloading).

DSL

Short for Digital Subscriber Line, which is a data communications technology that transmits information over the existing copper telephone lines (POTS). DSL takes existing voice cables that connect customer premises (CPE) to the phone company's central office (CO) and turns them into a high-speed digital linke. There are many types of DSL and ADSL is one of them.

DSLAM

Short for Digital Subscriber Line Access Multiplexer, a mechanism at a phone company's central location that links many customer DSL connections to a single high-speed ATM line.

When the phone company receives a DSL signal, an ADSL modem with a POTS splitter detects voice calls and data. Voice calls are sent to the PSTN, and data re sent to the DSLAM, where it passes through the ATM to the Internet, then baack through the DSLAM and ADSL modem before returning to the customer's PC.

Firmware

Software (programs or data) that has been written onto read-only memory (ROM). Firmware is a combination of software and hardware.

G.dmt

A kind of asymmetric DSL technology, based on DMT modulation, that offers up to 8 megabits per second downstream bandwidth, 1.544 Megabits per second upstream bandwidth. "G.dmt" is actually a nickname for the standard officially known as ITU-T Recommendation G.992.1.

EN/LZT 108 6429 R1

45 (47)

May 2003