DIGITAL SUBSCRIBER LINE -- DSL

A technology that increases the digital capacity of ordinary telephone lines (the local loops) into the home or office for Internet and TV service. Depending on the DSL version, speed is based on the distance between the customer and telco central office or telephone junction box.

DSL provides "always-on" operation. At the central office, DSL traffic is aggregated in a unit called the DSL Access Multiplexor (DSLAM) and forwarded to the appropriate ISP or data network. DSL arrived in the late 1990s with more version alphabet soup than most any other new transmission technology.

Asymmetric: Fast Down - Slow Up

ADSL - (Asymmetric DSL)

ADSL shares ordinary telephone lines by using higher frequencies than human speech. To eliminate interference, the first DSL deployments required a technician from the phone company to install a splitter that divided the line into separate DSL and phone lines. Subsequent splitterless versions (known as G.Lite, Universal ADSL and ADSL Lite) eliminated the support visit but require the user to plug filters

into every phone outlet.

ADSL is available in two modulation schemes: Discrete Multitone (DMT) or Carrierless Amplitude Phase (CAP).

ADSL Transmission

The higher frequencies of DSL have to be filtered out for regular telephones, answering and fax machines.

The Filter

Low-pass DSL filters split the line between phone and DSL modem. When DSL is installed, every telephone and answering machine must plug into the filter.

RADSL (Rate Adaptive DSL)
RADSL is a version of ADSL that adjusts speeds based on signal quality. Many ADSL technologies are actually RADSL.


VDSL/VHDSL (Very High Bit Rate DSL)
VDSL 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 their existing copper wires without having to replace them with optical fibers. Like ADSL, VDSL can share the line with the telephone.

Whereas VDSL achieves 50 Mbps transmission speed at 1,000 feet, VDSL2 extended the length of the path to 3,300 feet and delivers 100 Mbps at 1,600 feet. See G.fast.

Symmetric - Same Speed Both Ways

HDSL (High Bit Rate DSL)
HDSL provides T1 transmission over copper wires without the additional provisioning required for setting up T1 circuits, such as bridged tap removal and repeater installation. HDSL requires two cable pairs up to 12,000 feet, while HDSL-2 requires only one cable pair and spans 18,000 feet. HDSL does not allow line sharing with analog phones.


SDSL (Symmetric DSL)
SDSL is an HDSL variation that is rate adaptive, uses one cable pair and is offered in speeds from 144 Kbps to 1.5 Mbps. Like HDSL, SDSL does not share lines with analog phones.


IDSL (ISDN DSL)
IDSL is a slightly faster basic BRI ISDN service. It uses the 16 Kbps "D" channel for data rather than call setup to achieve 144 Kbps instead of 128 Kbps. 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 existing BRI terminal adapters and routers. See ISDN.

Quad-Band- 850/900/1800/1900 GSM/GPRS/EDGE

High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing 3G mobile telecommunication networks utilizing the WCDMA protocols.
 
GSM

Global System for Mobile Communication.

GSM is the dominant 2G digital mobile phone standard for most of the world. It determines the way in which mobile phones communicate with the land-based network of towers.

GSM is one of two major mobile phone technologies in the U.S. The other is CDMA. Cingular and T-Mobile use GSM. Sprint and Verizon use CDMA. GSM is more prevalent in most other parts of the world, and especially in Europe.

Although GSM and CDMA provide similar basic features and services to end-users, (such as voice calling, text messaging, and data services,) they operate very differently at many technical levels. This makes GSM phones completely incompatible with CDMA networks, and vice-versa.

The most visible feature of GSM are SIM cards. SIM cards are removable, thumbnail-sized smart cards which identify the user on the network, and can also store information such as phone book entries. SIM cards allows users to switch phones by simply moving their SIM card from one phone to the other.

GPRS

General Packet Radio Service.

A packet-switched technology that enables data communications.

GPRS is used for various data applications on phones, including wireless Internet (WAP), MMS, and software that connects to the Internet. Basically, any network connection that is not voice or text messaging uses a data connection like GPRS.

GPRS offers a tenfold increase in data speed over previous (circuit-switched) technologies, up to 115kbit/s (in theory). Typical real-world speeds are around 30-40 Kbps.

Newer technologies like EDGE and 3G are much faster.

See: EDGE

Using a packet switching, subscribers are always connected and always on-line, so services will be easy and quick to access.

GPRS is considered a "2.5G" technology, meaning it is more advanced than standard 2G digital technology, but does not meet the requirements of a full-feldged 3G technology.

EDGE

Enhanced Data for Global Evolution.

An upgrade for GSM/GPRS networks that triples data rates (speed) over standard GPRS.

EDGE is used automatically when both the phone and network support it. EDGE phones will automatically revert to the slower GPRS standard when EDGE service is not available.

Although many EDGE phones and devices are theoretically capable of up to 236 Kbps, most EDGE networks are only configured to allow up to 135 Kbps, to conserve spectrum resources. Real-world data rates are usually lower than the maximum.

Because it is based on existing GSM technology, EDGE is a smooth upgrade for GSM network operators. It also works within existing spectrum, making it ideal for countries without dedicated 3G spectrum, such as the US.

Although EDGE works at a low level within the GSM standard that includes voice, the main benefit is to increase GPRS data rates. GPRS operating over EDGE is called EGPRS.

Quad-Band

Designates a GSM phone that supports all four major GSM frequency bands, making it compatible with all major GSM networks worldwide.

The four bands include the 850 and 1900 MHz bands - used in the Americas - and 900 / 1800, used in most other parts of the world.

Compared to a tri-band phone supporting the 900 / 1800 / 1900 bands, a quad-band phone adds support for GSM 850 for full coverage in the Americas.

Compared to a tri-band phone supporting the 850 / 1800 / 1900 bands, a quad-band phone adds support for GSM 900 for full coverage in Europe and Asia.