16.13. SHDSL

You can find the SHDSL Settings at Interfaces → Assign → SHDSLs.

SHDSL stands for Symmetric Digital Subscriber Line and is responsible for the transmission of digital data over the copper wires of the telephone network. The following options can be changed:

Enabled to enable or disable the modem. It is highly recommended to disable the modem if it is not in use. The power consumption is much higher when the modem is searching for a connection.

Mode can be either Master (CO) or Slave (CPE).

Annex can be A or B.

EF Emergency Freeze can be on or off and is on by default. Emergency Freeze will stop data transmission and freeze the connection in order to prevent connection loss on bad signals.

PAM is the Pulse-amplitude modulation and auto by default.

Bitrate is auto by default.

Bitrate Mode is extended by default.

SNRM Target is the Signal-to-noise ratio Target and default by default.

SNRM Threshold is the Signal-to-noise ratio Threshhold and auto by default.

16.13.1. SHDSL Tuning

The SHDSL modem will try and find the right connection settings. If that takes longer than 5 minutes, you should go ahead and tune the parameters manually.

PAM is influenced by the quality of your DSL cable. Bitrate is influenced by the lenght of your DSL cable.

Depending on your cable you should start tweaking one or both settings.

SNRM should be between 6 and 9db or for very harsh environments 12db. The SNRM threshhold gives an upper bound if the quality of the DSL line is not always the same. Until this value the connection will not be terminated if it only fluctuates briefly.

To find the optimal speed you need to tune PAM and Bitrate if autodetect does not work. It is a 2 dimensional problem, where the amplitude (PAM) is the y axes and the speed (Bitrate) is the x axes of the wave that is used for the DSL signal.

Speed can be gained by a higher amnplitude (PAM) if the cable has a good quality or by speed (Bitrate) if the cable is not too long.