- Asked 3/10
- 2072 Magh · 10 marks
- 2073 Magh · 4 marks
- 2070 Bhadra · 4 marks
xDSL access technologies and types
Short answer
xDSL technologies provide high-speed digital access over existing copper lines. Main types include ADSL (asymmetric, up to 24 Mbps), SDSL (symmetric), and VDSL (very high, up to 100 Mbps). A splitter separates voice and data; DSLAM at the exchange connects lines to the ISP backbone.
Discuss the different xDSL technologies. (List the DSL access technologies with their types.)
DSL (Digital Subscriber Line) technologies give high-speed digital access over the ordinary copper telephone line by using higher frequencies than voice. The "x" stands for the different types. A splitter/filter separates voice (0-4 kHz) from data, so the phone and internet work at the same time. Speed falls as the distance from the exchange increases.
Main types
| Type | Full name | Downstream / upstream | Distance | Notes |
|---|---|---|---|---|
| ADSL | Asymmetric DSL | up to 8 Mbps / 1 Mbps | up to 5.5 km | Home internet; uses 1 pair; shares line with voice |
| ADSL2 | ADSL second gen | 12 Mbps / 1 Mbps | 5.5 km | Better modulation and diagnostics |
| ADSL2+ | 24 Mbps / 1 Mbps | 3 km | Doubles bandwidth to 2.2 MHz | |
| G.Lite (ADSL Lite) | Splitterless ADSL | 1.5 Mbps / 512 kbps | 5.5 km | No splitter needed; easy home install |
| RADSL | Rate-adaptive DSL | 0.6-7 Mbps / 128 kbps-1 Mbps | 5.5 km | Rate set by line quality |
| HDSL | High-bit-rate DSL | 1.544 / 2.048 Mbps both ways | 3.6 km | Symmetric, uses 2-3 pairs; replaces T1/E1; no voice |
| SDSL | Symmetric DSL | 1.544 / 2.048 Mbps both ways | 3 km | 1 pair; businesses |
| IDSL | ISDN DSL | 144 kbps both ways | 5.5 km | Digital data only |
| VDSL | Very-high-bit-rate DSL | 13-52 Mbps / 1.5-2.3 Mbps | 300 m-1.5 km | Fibre-to-the-curb |
| VDSL2 | up to 100 Mbps both ways | under 500 m | IPTV, triple play |
Features common to xDSL
- Uses the existing copper pair, so no new cable is needed.
- Always on, no dial-up, with a separate voice channel (in ADSL).
- Uses DMT or CAP modulation; a modem at the user end and a DSLAM at the exchange connect many lines to the ISP backbone.
- Asymmetric types (ADSL, VDSL) suit internet browsing and downloads; symmetric types (HDSL, SDSL) suit business servers and leased-line replacement.
PC--[DSL modem]--splitter--copper--[DSLAM]--ISP network
Phone-------------+ (voice goes to PSTN switch)
Limits: speed depends on distance and line quality, and there is interference (crosstalk). In Nepal, ADSL/VDSL service is provided by Nepal Telecom and ISPs.
✓ Answer checked by Claude Opus 5.5 (high effort)