 |
|
 |
|
|
|
| Results found for: DSL |
|
| DSL |
|
(2) See domain-specific language.
(1) (Digital Subscriber Line) A technology that dramatically increases the digital capacity of ordinary telephone lines (the local loops) into the home or office. DSL speeds are tied to the distance between the customer and the telco central office. DSL is geared to two types of usage. Asymmetric DSL (ADSL) is for Internet access, where fast downstream is required, but slow upstream is acceptable. Symmetric DSL (SDSL, HDSL, etc.) is designed for short haul connections that require high speed in both directions.
Unlike ISDN, which is also digital but travels through the switched telephone network, DSL provides "always-on" operation. At the telco central office, DSL traffic is aggregated in a unit called the DSL Access Multiplexor (DSLAM) and forwarded to the appropriate ISP or data network.
Although DSL only arrived in the very late 1990s, there have been more versions and alphabet soup than most any other new transmission technology. The major DSL flavors are summarized here:
ADSL
Asymmetric DSL shares the same line as the telephone, because it uses higher frequencies than the voice band. However, a POTS splitter must be installed on the customer's premises to separate the line between voice and ADSL. A version of ADSL, known as G.lite, Universal ADSL, ADSL Lite and splitterless ADSL, is geared to the consumer. It eliminates the splitter and associated installation charge, but all phones on the line must plug into low-pass filters to isolate them from the higher ADSL frequencies. ADSL is available in two modulation schemes: Discrete Multitone (DMT) or Carrierless Amplitude Phase (CAP). See ATU-C and ATU-R.
RADSL
Rate Adaptive DSL is a version of ADSL that adjusts speeds based on signal quality. Many ADSL technologies are actually RADSL.
VDSL (also VHDSL)
Very High Bit Rate DSL is an asymmetric version of DSL that is used as the final drop from a fiber optic junction point to nearby customers. VDSL lets an apartment or office complex obtain high-bandwidth services using existing copper wires without having to replace the infrastructure with optical fiber. Like ADSL, VDSL can share the line with the telephone.
HDSL
High Bit Rate DSL is a symmetric technology, which provides the same transmission rate in both directions. HDSL is the most mature DSL, because it has been used to provide T1 transmission over existing twisted pair without requiring the additional provisioning required for setting up T1 circuits. HDSL requires two cable pairs and goes up to 12,000 feet, while HDSL-2 requires only one cable pair and supports distances up to 18,000 feet. HDSL does not allow line sharing with analog phones.
SDSL
Symmetric DSL is an HDSL variation that uses only one cable pair and is offered in a wide range of speeds from 144 Kbps to 1.5 Mbps. SDSL is a rate adaptive technology, and like HDSL, SDSL cannot share lines with analog telephones.
IDSL
ISDN DSL offers a rather low speed (144 Kbps) in both directions compared to other symmetric versions, but it does provide 16 Kbps more than standard ISDN, because the 16 Kbps "D" channel is used for data rather than call setup. It also offers the longest distance of 26,000 feet. Unlike standard ISDN, IDSL does not support analog phones, and signals are not switched through the telephone network. Since IDSL uses the same 2B1Q line coding as ISDN, ISDN customers can use their existing equipment (ISDN BRI terminal adapters and routers) when connecting to IDSL.
ADSL Transmission
Using different frequencies in the line, ADSL allows data to ride over the same wires as voice conversations. The signals are combined and split apart at both sides. At the customer's site, the splitting is done either with an external device that must be installed by the telephone company, or it is built into the DSL modem.
|
|
Entries before DSL
DS3
DS4
DSA
DSD
DSD AC-3
|
|
Entries after DSL
DSLAM
DSML
DSOM
DSP
DSR
|
|
|
|
|
|
|
|
|
.gif)
