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100BaseT. A 100-Mbps local area network that maintains
backward compatibility with 10BaseT networks running at 10 Mbps.
10BaseT. A 10-Mpbs Ethernet local area
network that runs over twisted pair wiring. This network interface was originally designed to run over ordinary twisted pair (phone wiring) but is predominantly used with Category 3 or 5 cabling.
access rate. The
transmission speed of the physical access circuit between the end user location and the local network. This is generally measured in bits per second. Also called "access speed."
adapter card. Circuit board or
other hardware that provides the physical interface to a communications network; an electronics board installed in a computer that provides network communication capabilities to and from that computer; a card that
connects the DTE to the network. Also called a "network interface card" (NIC). See also data terminal equipment and network interface card.
ADSL Forum. The organization that
develops and defines xDSL standards, including those affecting ADSL, SDSL, HDSL, and VDSL. On the Internet, visit at http://www.adsl.com/.
asynchronous transmission. Data transmission of one character at a time to the receiving device, with intervals of varying lengths between transmittals, and with start bits at the
beginning and stop bits at the end of each character, to control the transmission. In xDSL and in most dial-up modem communications, asynchronous communications are often found in Internet access and remote office
applications. See also synchronous transmission.
ATM. Asynchronous Transfer Mode. A protocol
that packs digital information into 53-byte cells (5-byte header and 48-byte payload) that are switched throughout a network over virtual circuits. Standardized by the ITU-T in 1988 to create a Broadband Integrated
Services Digital Network (B-ISDN). Its ability to accommodate multiple types of media (voice, video, data) makes it a likely player for full service networks based on ADSL and VDSL.
ATM Forum. The organization tasked
with developing and defining ATM standards. On the Internet, visit at http://www.atmforum.com for more info.
bandwidth.
This is a reflection of the size or the capacity of a given transmission channel. In digital transmission, bandwidth is normally described in bits per second.
broadband. A type of
transmission that shares the bandwidth of a medium--such as copper or fiber optic cable--to carry more than one signal. Broadband facilities have a bandwidth (capacity) greater than a voice grade line of 3 kHz. Such
a broadband facility--typically coaxial cable--may carry numerous voice, video and data channels simultaneously. Each "channel" will take up a different frequency on the cable. "Guardbands"
(empty spaces) exist between the channels to make sure that each channel does not interfere with its neighbor. A coaxial CATV cable is the "classic" broadband channel. Simultaneously it carries many TV
channels. Broadband cables are used in some office LANs. But more common are the baseband variety, which have the capacity for one channel only. Everything on that cable to be transmitted or received must use that
one channel. That one channel is very fast, so each device needs only to use that high speed channel for only a little of the time. (The problem is getting on the channel.) See also baseband.
central office (CO).
A circuit switch that terminates all the local access lines in a particular geographic serving area; a physical building where the local switching equipment is found. xDSL lines running from a subscriber's home
connect at their serving central office.
channel. A generic term for a
communications path on a given medium; multiplexing techniques allow providers to put multiple channels over a single medium. See also multiplexer.
customer. Covad™ uses the
term "customer" when referring to the employees and subscribers of Covad's partners. Covad uses the term "partner" when referring to corporations and Internet Service Providers (ISPs) that have
contracted with Covad for service.
partner. Covad uses the term
"partner" when referring to corporations and Internet Service Providers (ISPs) that have contracted with Covad for service. Covad uses the term "customer" when referring to the employees and subscribers of these partners.
dedicated line.
A transmission circuit that is reserved by the provider for the full-time use of the subscriber. Also called a "private line."
dial up. The process of
initiating a switched connection through the network; when used as an adjective, this is a type of communication that is established by a switched-circuit connection.
digital subscriber line access multiplexer (DSLAM).
The technical description of the Hitchhiker system. Also called "service access multiplexer." The DSLAM uses digital subscriber line (xDSL) and asynchronous transfer mode (ATM) technologies to
deliver high speed data rates over the existing copper network. See also Hitchhiker, xDSL, and ATM. For an extensive description of the Hitchhiker system, refer to The Hitchhiker System manual from Diamond Lane Communications Corporation.
downstream/upstream
- downstream. In xDSL, the communications from the network
towards the customer premises.
- upstream. In xDSL, the communications
from the customer site up into the telecommunications network.
DSL. Digital Subscriber Line. A
general term for any local network loop that is digital in nature; technically, DSL equates to ISDN BRI, but this is decreasingly enforced terminology. DSL technology is available in several varieties. See also ADSL, HDSL, IDSL, RADSL, SDSL, VDSL, xDSL.
- ADSL. Asymmetric Digital Subscriber Line. A term for one-way
T1 transmission of signals to the home over the plain old, single twisted-pair wiring already going to homes. ADSL modems attach to twisted pair copper wiring. ADSL is often provisioned with greater downstream
than upstream rates (hence "asymmetric"). These rates are dependent on the distance a user is from the central office and may vary from as high as 9 Mbps to as low as 384 Kbps.
- HDSL. High bit-rate Digital Subscriber Line. The oldest of
the DSL technologies, HDSL continues to be used by telephone companies deploying T1 lines at 1.5 Mbps and requires two twisted pairs.
- IDSL. ISDN Digital Subscriber Line. IDSL provides up to 144-Kbps
transfer rates in each direction and can be provisioned on any ISDN capable phone line. Unlike ADSL and other DSL technologies, IDSL can be deployed regardless of the distance the user is from the central
office.
- RADSL. Rate Adaptive Digital Subscriber Line. Using modified
ADSL software, RADSL makes it possible for modems automatically and dynamically to adjust their transmission speeds. This often allows for good data rates for customers residing greater distances from the CO.
- SDSL. Single-line Digital Subscriber Line or Symmetric
Digital Subscriber Line. A modified HDSL software technology, SDSL is intended to provide 1.5 Mbps in both directions over a single twisted pair. However, the distance over which this can be achieved is less
than 8,000 feet.
- VDSL. Very high-rate Digital Subscriber Line. The newest of the DSL
technologies, VDSL can offer speeds up to 25 Mbps downstream and 3 Mbps upstream. Similar to SDSL, the gain in speed can be achieved only at short distances. These maximum speeds can be achieved only up to 1,000
feet. Sometimes also called broadband digital subscriber line (BDSL).
- xDSL. A generic term for the suite of
digital subscriber line (DSL) services, where the "x" can be replaced with any of a number of letters. See also DSL, ADSL, HDSL, IDSL, MDSL, RADSL, SDSL, VDSL.
DSU/CSU. Data Service Unit/Channel
Service Unit. The devices used to access digital data channels are called DSU/CSUs (Data Service Unit/Channel Service Units). At the customer's end of the telephone connection, these devices perform much the same
function for digital circuits that modems provide for analog connections. For example, DSU/CSUs take data from terminals and computers, encode it, and transmit it down the link. At the receive end, another DSU/CSU
equalizes the received signal, filters it, and decodes it for interpretation by the end-user.
DS1/DS3. Like T1 or T3 connections.
- T1. A digital transmission link with a capacity of
1.544 Mbps. T1 uses two pairs of normal twisted wires, the same as found in most residences. T1 normally handles 24 voice conversations, each one digitized at 64 Kbps. But, with more advanced digital voice
encoding techniques, it can handle more voice channels. T1 is a standard for digital transmission in the United States. T1 lines are used to connect networks across remote distances. Bridges and routers are used
to connect LANs over T1 networks. There are faster services available. T1 links can often be connected directly to new PBXs and many new forms of short haul transmission, such as short haul microwave systems.
- T3. A T3 line consists of 28 T1 lines or
44.736 million bits per second (commonly referred to as 45 Mbps). A T3 line can handle 672 voice conversations. T3 runs on fiber optic and is typically called FT3. See also T1.
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