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DSL-Corner: Line codes for various flavors of DSL
Overview
DSL, or Digital Subscriber Line, is a data communication techniques to transport high bitrates via ordinary telephony wiring. A typical telephony cable is build-up from twisted pairs (two copper wires, mutually twisted).Different flavours of DSL have been standardized, including:
| names | modulation | wire pairs | transition band |
| HDSL | PAM 2B1Q CAP/QAM, FDD |
3 2 1 |
|
| SDSL or SHDSL | TC-PAM (multilevel), FDD | 1 or multiple | bitrate dependent mostly below 1 MHz |
| ADSL, ADSL2, | DMT, FDD | 1 | 0 - 1.1 MHz |
| ADSL2plus | DMT, FDD | 1 | 0 - 2.2 MHz |
| VDSL | CAP/QAM, FDD DMT |
1 | above 1.1 MHz |
| VDSL2 | DMT, FDD | 1 2 (bonded) |
numerous, up to profile 35b |
| G.fast | DMT, TDD | 1 | 106MHz (current) 159MHz, 212MHz, 424MHz(future?) |
ADSL, SDSL and HDSL are getting out-dated. VDSL is widely deployed beyond 100Mb/s, and G.fast will bring that beyond 500MHz over a single wire pair .