Q1: What is SHDSL?
A1: SHDSL stands for "Single-pair
High-speed Digital Subscriber Line". It was developed to be
the convergence of symmetric DSL technologies (HDSL, SDSL, HDSL-2)
into a single internationally recognized industry standard.
SHDSL has been designed to improve reach performance and Power Spectral
compatibility with other DSL technologies (ADSL, etc.).
User (payload) data rates are identical
in both upstream and downstream directions (symmetric technology)
and vary from:
- 192 Kb/s to 2.3 Mb/s in two-wire (one pair) mode,
- 384 Kb/s to 4.6 Mb/s in four-wire (two pair) mode.
Q2: Is SHDSL a standardized technology?
A2: Yes, SHDSL is an International
Telecommunication Union (ITU) Recommendation. It is described in
It relies on G.994.1 (Handshake procedures for Digital Subscriber
Line transceivers) for the pre-activation phase.
Q3: What about POTS, ISDN, splitters,
A3: In ADSL part of the bandwidth
is reserved for POTS or ISDN.
In SHDSL this is not the case, all the bandwidth is used, so the
line is totally dedicated to the SHDSL service.
There is therefore no need for splitters.
Q4: What is "EOC"?
A4: EOC = Embedded Operations Channel.
The SHDSL DSLAM, the CPE, and the repeaters can communicate through
For instance the DSLAM can send the following types of EOC requests:
- inventory, to get information (Manufacturer, release, etc.), about
the remote CPE,
- enable/disable network loopbacks on the CPE,
- ask the CPE to report statistics or failure information (SNR Margin,
loop attenuation, number of CRC errors, etc.).
The EOC messages are defined in G.991.2
to provide interoperability.
Q5: What is SHDSL "auto-adaptive rate"
A5: Normally in SHDSL the line rate
is fixed by configuration at the DSLAM side. For instance : 2048
Kbits/s. So it links at that configured rate or it doesn't link
at all. This is because SHDSL's target is more business services,
replacement of E1 and T1 lines and so on... where the rate is supposed
to be known and guaranteed.
However, due to the strong "ADSL habits" in the field, some manufacturers
propose a "auto-adaptive rate" mode for SHDSL. In this case the
DSLAM and the CPE try to link up at (quite) the best possible rate
for the current line conditions.
Q6: What are SHDSL Thomson products?
Learn more about the SpeedTouch products.