Single-pair high-speed digital subscriber line (SHDSL) is a form of
symmetric digital subscriber line (SDSL), a data communications technology for equal transmit and receive (i.e. symmetric) data rate over
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
telephone line
A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or ot ...
s, faster than a conventional
voiceband
A voice frequency (VF) or voice band is the range of audio frequencies used for the transmission of speech.
Frequency band
In telephony, the usable voice frequency band ranges from approximately 300 to 3400 Hz. It is for this reason that ...
modem
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...
can provide. As opposed to other DSL technologies, SHDSL employs
trellis-coded pulse-amplitude modulation (TC-PAM). As a
baseband
In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into a ...
transmission scheme, TC-PAM operates at frequencies that include those used by the analog voice
plain old telephone service
Plain old telephone service (POTS), or plain ordinary telephone system, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. POTS was the standard service offering from telephone companies from 1 ...
(POTS). As such, a frequency splitter, or
DSL filter
A DSL filter (also DSL splitter or microfilter) is an analog low-pass filter installed between analog devices (such as telephones or analog modems) and a plain old telephone service (POTS) line. The DSL filter prevents interference between su ...
, cannot 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 made SHDSL a popular choice by businesses for
private branch exchange
A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX).
A business telephone syst ...
(PBX),
virtual private network
A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. The be ...
(VPN),
web hosting
A web hosting service is a type of Internet hosting service that hosts websites for clients, i.e. it offers the facilities required for them to create and maintain a site and makes it accessible on the World Wide Web. Companies providing web h ...
and other data services.
SHDSL features symmetrical
data rates
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. ...
in both the
upstream
Upstream may refer to:
* Upstream (bioprocess)
* ''Upstream'' (film), a 1927 film by John Ford
* Upstream (networking)
* ''Upstream'' (newspaper), a newspaper covering the oil and gas industry
* Upstream (petroleum industry)
* Upstream (software ...
and
downstream
Downstream may refer to:
* Downstream (bioprocess)
* Downstream (manufacturing)
* Downstream (networking)
* Downstream (software development)
* Downstream (petroleum industry)
* Upstream and downstream (DNA), determining relative positions on DNA ...
directions, from 192 kbit/s to 2,312 kbit/s of
payload
Payload is the object or the entity which is being carried by an aircraft or launch vehicle. Sometimes payload also refers to the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of ...
in 8 kbit/s increments for one pair and 384 kbit/s to 4,624 kbit/s in 16 kbit/s increments for two pairs of wires. The reach varies according to the
loop
Loop or LOOP may refer to:
Brands and enterprises
* Loop (mobile), a Bulgarian virtual network operator and co-founder of Loop Live
* Loop, clothing, a company founded by Carlos Vasquez in the 1990s and worn by Digable Planets
* Loop Mobile, an ...
rate and
noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
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 5,696 kbit/s on one pair, using the 32-TC-PAM modulation scheme specified in Annexes F and G. Using M-pair bonding, up to four pairs of wires may be bonded to yield data rates up to M×5,696 kbit/s. In this way, a single SHDSL interface using four bonded wire pairs can carry up to 22,784 kbit/s.
The SHDSL payload may be either 'clear channel' (unstructured),
T1 or
E1 (full rate or fractional), multiple
ISDN
Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Wo ...
Basic Rate Interface
Basic Rate Interface (BRI, 2B+D, 2B1D) or Basic Rate Access is an Integrated Services Digital Network (ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for voice-grade telephone service ...
(BRI),
Asynchronous Transfer Mode
Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by American National Standards Institute (ANSI) and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of ...
(ATM) cells or
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
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
The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...
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
HDSL High-bit-rate digital subscriber line (HDSL) is a telecommunications protocol standardized in 1994. It was the first digital subscriber line (DSL) technology to use a higher frequency spectrum over copper, twisted pair cables. HDSL was developed to ...
symmetric DSL technology defined in ITU-T G.991.1. SHDSL has largely been replaced by
VDSL2
Very high-speed digital subscriber line (VDSL) and very high-speed digital subscriber line 2 (VDSL2) are digital subscriber line (DSL) technologies providing data transmission faster than the earlier standards of asymmetric digital subscriber lin ...
because of greater bandwidth, less interference and greater utilization.
In
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, a variant of SHDSL was standardized by the
European Telecommunications Standards Institute
The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of Information and communications technology, information and communications. ETSI supports the developmen ...
(ETSI) using the name 'SDSL'. This ETSI variant is compatible with the
ITU-T
The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...
SHDSL standardized regional variant for Europe and must not be confused with the usage of the term SDSL in North America to refer to
symmetric digital subscriber line.
External links
ITU-T Recommendation G.991.2: Single-pair high-speed digital subscriber line (SHDSL) transceivers
{{DSL technologies
Digital subscriber line
ITU-T recommendations
ITU-T G Series Recommendations
Telecommunications-related introductions in 2001