Broadband Internet Technologies : Wired Broadband : Digital Subscriber Line: G.Lite, Radsl, Vdsl
2. G.Lite (also known as DSL Lite, splitterless ADSL, and Universal ADSL):
It is essentially a slower ADSL that doesn't require splitting of the line at the user end but manages to split it for the user remotely at the telephone company. This saves the cost of what the phone companies call "the truck roll." G.Lite, officially ITU-T standard G-992.2, provides a data rate from 1.544 Mbps to 6 Mpbs downstream and from 128 Kbps to 384 Kbps upstream. G.Lite is expected to become the most widely installed form of DSL.
ADSL Lite uses the Discrete Multi-Tone (DMT) modulation technique. The DMT line code uses a set of tones to send data over the line and allocates more data to those frequencies where there are less analog impairments. The data is then reassembled by the modem at the other end of the line. ADSL Lite modems also interleave the serial bit stream of data, thus facilitating error correction by providing protection against noise bursts at the cost of higher latency.
3. RADSL (Rate-Adaptive Asymmetric Digital Subscriber Line):
RADSL is an implementation of ADSL that automatically adjusts the connection speed to adjust for the quality of the telephone line. This feature allows RADSL service to function over longer distances than does ordinary ADSL, an important feature in suburban neighborhoods.
In RADSL, the broadband modem is configured at startup to test the phone line and adjust the data rate. RADSL typically operates at a lower date rate than regular ADSL. Like ADSL, RADSL provides relatively more bandwidth for downloads and less for uploads.
4. VDSL (Very-high-speed Digital Subscriber Line):Also known as VADSL and BDSL
It was developed to support exceptionally high-bandwidth applications such as High-Definition Television (HDTV). VDSL is not as widely deployed as other forms of DSL service. However, VDSL can achieve data rates up to approximately 51,840 Kbps, making it the fastest available form of DSL.
To perform at this speed, VDSL relies on fiber optic cabling. VDSL is designed to work more as a business service that uses ATM internetworking rather than as a consumer service that utilizes IP. VDSL supports both voice and data communication on the same line, like other forms of DSL.
Also like most DSL technology, the performance of VDSL depends significantly on the physical distance traversed by wires: Shorter distances mean faster networking. The technology was originally named VADSL ('A' for asymmetric), but VDSL has now been improved and can operate in either symmetric or asymmetric modes.
The key to VDSL is that the telephone companies are replacing many of their main feeds with fiber-optic cable. In fact, many phone companies are planning Fiber to the Curb (FTTC) , which means that they will replace all existing copper lines right up to the point where your phone line branches off at your house. At the least, most companies expect to implement Fiber to the Neighborhood (FTTN). Instead of installing fiber-optic cable along each street, FTTN has fiber going to the main junction box for a particular neighborhood.