ADSL: Asymmetric DSL including both CAP and DMT.
CAP: CAP is a variation of quadrature amplitude modulation (QAM). With CAP, the plain-old telephone service (POTS) and upstream and downstream channels are supported by splitting the frequency spectrum. Many CAP products are based on Globespan chipsets.
DMT: DMT is the modulation technique specified in the American National Standards Institute (ANSI) T1E1.4 standard. DMT uses a large number, typically 256, of equally spaced sub-channels, each of which can be individually modulated by QAM with a variable number of levels. With DMT, the number of bits per carrier is assigned based on channel capacity. Chipset providers include TI, Motorola, ADI, and Alcatel.
G.lite (G.992.2): The ITU standard for splitterless ADSL modems. The technology is based on DMT and allows for client product to be implemented without a POTS splitter.
SDSL 2B1Q: It is based on high-speed DSL (HDSL) but only uses one twisted pair. It offers symmetrical speeds of over 192Kb.
IDSL 2B1Q: ISDN over an xDSL. It offers symmetrical speeds up to 128Kbps.
VDSL: A modem for twisted-pair access operating at data rates from 12.9 to 52.8 Mbps, with a corresponding maximum reach ranging from 1,000 to 4,500 feet of 24-gauge twisted pair.
HDSL (High Bit Rate Digital Subscriber Line) and HDSL2: HDSL enables full duplex
transmission at up to 2 Mbps over ordinary copper twisted pairs in unshielded cable. HDSL
products can use one, two or three twisted copper pairs for transmission. Some products
using this technology also offer 10 to 12 POTS connections over a single copper pair
instead of a T1/E1 interface and these systems are also included in this segment.
CPE/modem products: This is the unit that sits at the home, business, or end-user location that is receiving xDSL service.
Internal xDSL modem: This is a modem that would be placed inside of a PC. It is not a PCMCIA card.
External xDSL modem: This modem does not go inside of a PC. It has its own casing and is connected to the PC via a cable.
CPE xDSL router: This router is similar to an external xDSL modem but also includes routing functions.
DSL Access Multiplexer (DSLAM): This product is a chassis that contains xDSL line cards. The chassis can be located in a CO and sits outside of the CO switch.
CO switch line cards: xDSL-enabling line cards that are designed to reside within a CO switch
Digital Loop Carrier (DLC): The number of DSL ports shipped in Next Generation DLCs (NGDLC). DLCs extend the reach of a central office switch within the local loop. NGDLCs are advanced systems that support broadband services like DSL.
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