 |
This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2011) |
A DSL filter is an analog low-pass filter installed between analog devices (such as telephones or analog modems) and a plain old telephone service (POTS) telephone line, in order to prevent interference between such devices and a digital subscriber line (DSL) service operating on the same line. Without DSL filters, signals or echoes from analog devices at the top of their frequency range can result in reduced performance and connection problems with DSL service, while those from the DSL service at the bottom of its range can result in line noise and other issues for analog devices.
Typical installation for an existing home involves installing DSL filters on every telephone, fax machine, voice band modem, and other voiceband device in the home, leaving the DSL modem as the only unfiltered device. For wall mounted phones, the filter is in the form of a plate which hangs on the standard wall mount, and upon which the phone hangs in turn.
In cases where it is possible to run new cables, it can be advantageous to split the telephone line after it enters the home, installing a single DSL filter on one leg and running it to every jack in the home where an analog device will be in use, and dedicating the other (unfiltered) leg to the DSL modem. Some devices, such as monitored alarms and Telephone Devices for the Deaf, mainly certain older models using an acoustic coupler, may be hardwired and may not easily accept a DSL filter. Some of these devices can be successfully filtered with a DSL filter or splitter, especially if the hardwired connection is converted into a jacked connection.
Some DSL modems have filtering circuitry built-in, to which the telephones and fax machines can be connected.
Modulation techniques and specifications [link]
- ITU G.992.1 (G.DMT),
- ITU G.992.2 (G.Lite)
- ITU G.992.5 (G.DMT2+)
https://wn.com/DSL_filter
Asymmetric digital subscriber line
Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines rather than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL). Bandwidth (and bit rate) is greater toward the customer premises (known as downstream) than the reverse (known as upstream). This is why it is called asymmetric. Providers usually market ADSL as a service for consumers to receive Internet access in a relatively passive mode: able to use the higher speed direction for the download from the Internet but not needing to run servers that would require high speed in the other direction.
Overview
ADSL works by utilizing frequencies that are not used by a voice telephone call. A splitter, or DSL filter, allows a single telephone connection to be used for both ADSL service and voice calls at the same time. ADSL can generally only be distributed over short distances from the telephone exchange (the last mile), typically less than 4 kilometres (2 mi), but has been known to exceed 8 kilometres (5 mi) if the originally laid wire gauge allows for further distribution.
Adenylosuccinate lyase
Adenylosuccinate lyase (or adenylosuccinase) is an enzyme that in humans is encoded by the ADSL gene.
Adenylosuccinate lyase converts adenylosuccinate to AMP and fumarate as part of the purine nucleotide cycle. ASL catalyzes two reactions in the purine biosynthetic pathway that makes AMP; ASL cleaves adenylosuccinate into AMP and fumarate, and cleaves SAICAR into AICAR and fumarate.
Adenylosuccinate lyase is part of the β-elimination superfamily of enzymes and it proceeds through an E1cb reaction mechanism. The enzyme is a homotetramer with three domains in each monomer and four active sites per homotetramer.
Point mutations in adenylosuccinate that cause lowered enzymatic activity cause clinical symptoms that mark the condition adenylosuccinate lyase deficiency.
This protein may use the morpheein model of allosteric regulation.
Function
Adenylosuccinate lyase (ASL) is an enzyme that catalyzes two reactions in the de novo purine biosynthetic pathway. In both reactions it uses an E1cb elimination reaction mechanism to cleave fumarate off of the substrate. In the first reaction, ASL converts 5-aminoimidazole- (N-succinylocarboxamide) ribotide (SAICAR) to 5-aminoimidazole-4-carboxamide ribotide (AICAR) and fumarate. AICAR proceeds through three more reactions before it becomes adenylosuccinate (also called succinyladenosine monophosphate or SAMP), which ASL then splits into adenosine monophosphate (AMP) and fumarate. ASL is important to cells not only because of its involvement in creating purines needed for cellular replication, but also because it helps regulate metabolic processes by controlling the levels of AMP and fumarate in the cell.
G.992.3
ITU G.992.3 is an ITU (International Telecommunication Union) standard, also referred to as ADSL2 or G.dmt.bis. It optionally extends the capability of basic ADSL in data rates to 12 Mbit/s downstream and, depending on Annex version, up to 3.5 Mbit/s upstream (with a mandatory capability of ADSL2 transceivers of 8 Mbit/s downstream and 800 kbit/s upstream). ADSL2 uses the same bandwidth as ADSL but achieves higher throughput via improved modulation techniques. Actual speeds may reduce depending on line quality; usually the most significant factor in line quality is the distance from the DSLAM to the customer's equipment.
Annex versions
ADSL2 has multiple modes for DSL providers to offer services for different needs. Below is a list of available features based on ADSL2 specs from the ITU standards.
