single pair high bit rate digital subscriber line (DSL) (SHDSL)
Single Pair High Bit Rate Digital Subscriber Line (SHDSL) is a symmetrical DSL process for copper twisted pairs. The process offers transmission rates between 192 kbit/s and 2.312 Mbit/s and has been standardized by the International Telecommunication Union( ITU) under the G.991.2 standard. SHDSL technology is designed for transporting E1/ T1 signals, ISDN, ATM and IP data; it is used in Ethernet in the First Mile( EFM) and midband Ethernet, among other applications.
Before a transmission starts, a handshaking protocol(G.994.1) regulates which frame types are used. SHDSL uses TC- PAM 16 as coding, which occupies the frequency spectrum up to 400 kHz. The range of SHDSL at 2.3 Mbit/s over copper twisted pairs is about 3 km. When two twisted pairs are bundled, speeds of 4.6 Mbit/s can be achieved over this distance, and when four twisted pairs are bundled, data rates of as much as 9.2 Mbit/s can be achieved. However, with four twisted pairs, the range can also be extended to approximately 9 km at 2.3 Mbit/s. In addition, there is SHDSL.bis with which data rates of up to 19 Mbit/s can be achieved.
SHDSL allows a flexible combination of voice and data channels with the highest quality of service. The SHDSL process is also known as G.SHDSL, Global Standard for Single-Pair Highspeed Digital Subscriber Line, which was ratified by the ITU in 2001.