Technical data

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SDSL
SDSL (Symmetric Digital Subscriber Loop) and G.SHDSL are symmetrical xDSL tech-
nologies.
A distinguishing feature of these is that they have similar uploading and down-
loading rates, thus the name symmetrical. Using SDSL the user attains a maximum
of 2.3 Mbit/s in both directions. Symmetrical SDSL can be used in Back to Back mode,
which involves interconnecting two modems using copper cable. SDSL is a proprietary
technology mainly installed in North America. Industrial applications are starting to
switch to the international standard SHDSL, see below.
SHDSL
SHDSL stands for Symmetric High-Bitrate Digital Subscriber Loop, which is the first
international standard for Multi-Rate symmetrical DSL. SHDSL has been developed for
communication over one or more twisted wire pairs. Using a single wire pair produces
transfer rates between 192 kbit/s and 2.3 Mbit/s, while two pairs produce rates
between 384 kbit/s and 4.6 Mbit/s. SHDSL utilises an advanced coding algorithm, TC-
PAM, which results in improved transfer rates and/or transmission distances compared
with other DSL technologies.
Indication of transmission distances using SHDSL
Speed Distance
Communication over a single pair
AWG 26 192 kbit/s 6 km (3.72 mi)
Communication over a single pair
AWG 26 2.3 Mbit/s 3 km (1.86 mi)
Communication over two pairs
AWG 26 2.3 Mbit/s 5 km (3.10 mi)
When greater transmission distances are required, there is the possibility of
deploying a repeater between the devices.
Detailed information can be found in the standards:
… ANSI (T1E1.4/2001-174) for North America.
… ETSI (TS 101524) for Europe.
… ITU-T (G.991.2) worldwide.
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