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Comparing DSL Types
Submitted by mechanicaljackass on Tue, 12/16/2008 - 02:57.
There are several variations on DSL technology. In fact, there are so many that you will often see the term xDSL, where x is a variable, when the discussion is about DSL in general.
- * Asymmetric DSL (ADSL) - It is called "asymmetric" because the download speed is greater than the upload speed. ADSL works this way because most Internet users look at, or download, much more information than they send, or upload.
- * High bit-rate DSL (HDSL) - Providing transfer rates comparable to a T1 line (about 1.5 Mbps), HDSL receives and sends data at the same speed, but it requires two lines that are separate from your normal phone line.
- * ISDN DSL (ISDL) - Geared primarily toward existing users of Integrated Services Digital Network (ISDN), ISDL is slower than most other forms of DSL, operating at fixed rate of 144 Kbps in both directions. The advantage for ISDN customers is that they can use their existing equipment, but the actual speed gain is typically only 16 Kbps (ISDN runs at 128 Kbps).
- * Multirate Symmetric DSL (MSDSL) - This is Symmetric DSL that is capable of more than one transfer rate. The transfer rate is set by the service provider, typically based on the service (price) level.
- * Rate Adaptive DSL (RADSL) - This is a popular variation of ADSL that allows the modem to adjust the speed of the connection depending on the length and quality of the line.
- * Symmetric DSL (SDSL) - Like HDSL, this version receives and sends data at the same speed. While SDSL also requires a separate line from your phone, it uses only a single line instead of the two used by HDSL.
- * Very high bit-rate DSL (VDSL) - An extremely fast connection, VDSL is asymmetric, but only works over a short distance using standard copper phone wiring.
- * Voice-over DSL (VoDSL) - A type of IP telephony, VoDSL allows multiple phone lines to be combined into a single phone line that also includes data-transmission capabilities.
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Dude, you forgot to add
Dude, you forgot to add SHDSL.. :)
Single-pair High-speed Digital Subscriber Line (SHDSL) - is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. Compared to ADSL, SHDSL employs frequencies that include those used by traditional POTS telephone services to provide equal transmit and receive (i.e. symmetric) data rates. As such, a frequency splitter, or microfilter, can not be used to allow a telephone line to be shared by both an SHDSL service and a POTS service at the same time. Support of symmetric data rates has made SHDSL a popular choice by businesses for PBX, VPN, web hosting and other data services.
SHDSL features symmetrical data rates from 192 kbit/s to 2,304 kbit/s of payload in 64 kbit/s increments for one pair and 384 kbit/s to 4,608 kbit/s in 128 kbit/s increments for two pair applications. The reach varies according to the loop rate and noise conditions (more noise or higher rate means decreased reach) and may be up to 3,000 meters. The two pair feature may alternatively be used for increased reach applications by keeping the data rate low. Halving the data rate per pair will provide similar speeds to single pair lines while increasing the error/noise tolerance.
An optional extended SHDSL mode allows symmetric data rates up to 5696 kbit/s on one pair. Higher data rates may be achieved using two or up to four copper pairs.
The SHDSL payload may be either 'clear channel' (unstructured), T1 or E1 (full rate or fractional), multiple ISDN Basic Rate Access (BRA), Asynchronous Transfer Mode (ATM) cells or Ethernet packets. A 'dual bearer' mode allows a mixture of two separate streams (e.g. T1 and ATM) to share the SHDSL bandwidth.
-This type of DSL is quite sensitive. Although beneficial for SME's.