DSL
Glossary
ADSL (Asymmetric Digital Subscriber Line)
This service transmits data faster in one direction (1.544Mbps downstream to the home or
office) than the other (384Kbps upstream to the telephone company's CO). It enables
Internet users to rapidly download large files and other resources from the Web.
ATM Backbone
The XO backbone uses technology based on transferring data in packets of a fixed size. By
packetizing traffic into 53-byte cells, XO is able to provide very fast switches, which
allows video, audio and computer data to be transmitted over the same network, and assures
that no single type of data saturates the line. The ATM backbone is the equipment that
provides high-speed connectivity for users and includes this powerful network
infrastructure.
Adapter Card
An electronics board installed in a PC, which provides a network interface to and from
that computer. Also called a network interface card (NIC).
Bandwidth
The amount of information or data that can be sent over the Internet in a given period of
time. Bandwidth is usually stated in bits per second (bps), kilobits per second (Kbps) or
megabits per second (Mbps).
CLEC (Competitive Local Exchange Carrier)
A competitor to Incumbent Local Exchange Carrier (your local phone company) offering
telecommunications service.
CO (Central Office)
A local telephone company switching station that covers a geographic area, such as a
section of a city or a town. DSL lines running from a subscriber's home connect at the
central office.
CPE (Customer Premise Equipment)
Communications equipment that resides on the customer's premises. The CPE for DSL services
is a DSL modem.
Dedicated Line
A transmission circuit that is reserved by the provider for the full-time use of the
subscriber.
HDSL (High-Speed Digital Subscriber Line)
This service runs at approximately 6Mbps and is used to provide T-1 digital service
(1.544Mbps) over standard copper telephone lines.
IDSL (ISDN Digital Subscriber Line)
IDSL is designed to accommodate users that have already invested in ISDN. This service
provides ISDN signaling at 144Kbps over a DSL circuit, and plugs into existing ISDN
equipment at the local carrier's CO.
Kbps
A measure of bandwidth capacity or transmission speed. It stands for a thousand bits per
second.
Latency
A term used when measuring the delay from the time data is sent from its origination until
the data is received at its destination.
Local Area Network (LAN)
A network covering a small area, usually within a building or floors within a building.
Local Loop
A generic term for the connection between the customer's location (home or office) and the
provider's central office.
Mbps
A measure of bandwidth capacity or transmission speed. It stands for a million bits per
second.
Packet
A grouping of information that includes a header (containing information such as
destination address) and, in most cases, user data.
Plain Old Telephone Service (POTS)
This term commonly refers to standard telephony, as in placing and receiving telephone
calls.
RJ-11
A phone jack commonly used in phones, modems and fax machines.
RJ-45
An 8 pin connector used to attach data transmission devices to standard telephone wiring.
Commonly used in 10BaseT connections.
SDSL (Symmetric Digital Subscriber Line)
Also called single line service, SDSL provides 144Kbps of bandwidth in both directions at
an affordable cost (less than half that of ADSL services).
T1
This is a Bell system term for a digital carrier facility used for transmission of data
through the telephone hierarchy at a transmission rate of 1.544 Mbps.
T3
This is a Bell system term for a digital carrier facility used for transmission of data
through the telephone hierarchy at a transmission rate of 45 Mbps.
Telco
The local telephone company operator in a given area. In the U.S., the major telcos are
the seven regional Bell operating companies and the leading independents, GTE, SNET, and
Sprint.
Twisted Pair
A common form of copper cabling used for telephony and data communications.
VDSL (Very High-Speed Digital Subscriber Line)
This is the next generation of DSL that will take advantage of sophisticated new modems to
blast video and data over existing telephone company network infrastructures at speeds of
8Mbps to 53Mbps. When VDSL arrives, the age of multimedia in our homes and businesses will
have arrived.
xDSL
This generic acronym is used to refer to any of the flavors of DSL. The "x" can
be replaced with a variety of letters, such as "a" for asymmetric DSL and
"s" for symmetric DSL.
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