Single-pair high-speed digital subscriber line
Single-pair high-speed digital subscriber line (SHDSL) is a form of
SHDSL features symmetrical
With the 32-TC-PAM modulation scheme described in Annexes F and G, symmetric data rates of up to 5,696 kbit/s are permitted on one pair in the optional extended SHDSL mode. Up to four pairs of wires may be bonded using M-pair bonding to produce data rates as high as M5,696 kbit/s. By using four bonded wire pairs, a single SHDSL interface can transmit up to 22,784 kbit/s.
The SHDSL payload may be either 'clear channel' (unstructured), T1 or E1 (full rate or fractional), multiple ISDN Basic Rate Interface (BRI), 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.
SHDSL standards
The industry standard for SHDSL is defined by ITU-T recommendation G.991.2. This was first published in February 2001. SHDSL equipment is also known by the standard's draft name of G.SHDSL. Major updates to G.991.2 were released in December 2003. Equipment conforming to the 2003 version of G.991.2 is often referred to by the standard's draft name of G.SHDSL.bis or just SHDSL.bis. The updated G.991.2 features:
- Optional support for up to four copper pair connections (M-pair)
- Optional extensions to allow user data rates up to 5696 kbit/s per pair, described in Annexes F and G
- Optional support for dynamic rate repartitioning, allowing flexible change of the SHDSL data rate without service interruption, described in Annex E.10.3
- New payload definitions including Ethernet packet transfer mode (PTM), described in Annex E.11
SHDSL supersedes the older
In