DSL Modems Glossary

A thru H	Definition of Terms
Access Network	Portion of PSTN that connects access nodes to subscribers.  Predominantly twisted pair copper wiring.
Access Node	Points on edge of Access Network that concentrate individual access lines into a smaller number of feeder lines.
Access Router	Interfaces a LAN to a WAN.
ADSL	Asymmetric Digital Subscriber Line - one of a family of DSL technologies.  1.5-9Mbps downstream and 16-800kbps upstream, depending on distance.  A slower, less expensive version is known as ADSL Lite or G.lite.
ANSI	American National Standards Institute - U.S. telecom standards-setting organization.
ASSP	Application-Specific Standard Product - high-integration chip or chipset for a specific application.
ATM	Asynchronous Transfer Mode: cell-based transmission protocol.  Independent of the medium, it can be run over ADSL.  Can contain any type of information (voice, video, data).
ATU-C (ATU-R)	ADSL Transmission Unit, Central (or Remote).  Device directly connected to ADSL line.  The Central unit is typically housed with many others at the CO.  The Remote unit is at the customer, and can be a modem, NIC, or router.
Baseband	Using entire bandwidth of a medium to carry a single signal.
Broadband	Sharing the bandwidth of a medium to carry more than one signal; typically data rates above 1.5/2.0 Mbps.
CAP	Carrierless Amplitude/Phase modulation.  A two-dimensional passband line code derived from QAM.
CO	Central Office - telephone company equipment to terminate and interconnect customer lines.
Codec - Coder/Decoder	An assembly comprising an encoder and a decoder in the same unit.  A device that produces a coded output from an analog input, and vice versa.  In video, refers to compression and decompression.
Demodulation	Conversion of analog carrier signal to digital information.
DMT	Discrete Multi-Tone - modulation scheme in which available bandwidth is divided into sub-channels (256 for downstream), maximizing the use of the clearer channels.  Recently selected by ANSI and ETSI over CAP for ADSL standard.  DMT is a form of Frequency Division Multiplexing.
Downstream	Data recieved by the modem from the Internet.
DSL	Digital Subscriber Line.  Local digital network loop, typically sends high-speed data over standard phone lines.
DSLAM	DSL Access Multiplexer.  Takes many ADSL lines (ATU-C units) and concentrates them, typically to a single ATM line, typically at the CO.
Ethernet	10 Mbps LAN protocol.
ETSI	European Telecommunications Standards Institute - European telecom standards-setting organization.
FireWire	Standard high-speed serial bus.  Supports up to 400 Mbps today, going to 3200 Mbps, and plug-and-play.
G.lite	Lightweight version of ADSL limited to 1.5Mbps downstream but eliminating the need for a splitter.
HDSL	High data rate symmetric DSL - T1 or E1 speed achieve via multiple modems and short distances.
I thru P
IDSL	ISDN DSL (128kbps).
IEEE 1394	See FireWire.
ISDN	Integrated Services Digital Network - a digital network with circuit and packet switching for voice and data communications at data rates up to 2.048 Mbps.
LAN	Local Area Network - Small-area data communications network; typical protocols are Ethernet and Token Ring.
Loop	Twisted-pair copper telephone line.
MAC	Media Access Controller - The logic that controls access to the physical transmission medium (PHY) on a LAN.  Common MAC layer standards are the CSMA/CD architecture used in Ethernet and the token passing methods used in Token Ring, FDDI and MAP.
Modem	Modulator/demodulator converts digital data to/from analog signals for transmission over analog facilities.
NIC	Network Interface Card - Circuit board that interfaces between computer and the communications network.  In ADSL, commonly uses Ethernet to interface ADSL modem to the computer.
Packet	Sub-unit of a data stream; typically contains a header and user data, or payload.
Packet Switched Network	Network that does not establish a dedicated physical path, but transmits data in segments called packets.  Packets are sent over the best available network connection and then re-assembled at the endpoint.
PHY	Physical Layer Interface - Direct interface to the transmission medium.
PNA	Phone Networking Alliance - Home networking standard for 1-10 Mbps over phone wire.
POTS	Plain Old Telephone Service - analog phone service, takes the lowest 4KHz of bandwidth on loop.
PSTN	Public Switched Telephone Network.
Q thru Z
QAM	Quadrature Amplitude Modulation.  A method of encoding digital data in an analog signal in which each combination of phase and amplitude represent one of sixteen four-bit patterns.
RADSL	Rate-adaptive ADSL - ADSL version where modems test line at start up and adapt to fastest possible speed. All DSL modems based on DMT are inherently rate-adaptive.
Router	Connects multiple computer networks.
RS-232	Standard for serial transmission between a computer and peripherals for short distances.
SAR	Segmentation and Reassembly - Segmenting packets into payloads.
SDSL	Symmetric DSL - HDSL plus POTS over a single line.
Splitter	Filter to separate high-frequency ADSL and low-frequency POTS data.  Requires costly installation in home.  DSL G.Lite is splitterless, meaning it eliminates the need for an external splitter.
Universal ADSL	Another name for G.lite.  Also the name of the working group that developed it.
Upstream	Data transmitted from the modem to the Internet.
USB	Universal Serial Bus - Standard for serial transmission between a computer and peripherals.  Supports up to 12 Mbps and plug-and-play.
UTOPIA	Universal Test & Operations Interface for ATM - Refers to an electrical interface between the sublayers of the PHY layer.
VDSL	Very high data rate DSL - 12.9-52.8 Mbps at shorter distances.
WAN	Wide Area Network - Private network facilities usually offered by public telephone companies.
xDSL	Refers to all types of DSL.

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