User`s guide

SET UP
Page 30 User’s guide ref 9018809-01 XSRING+ SHDSL switch
9 SHDSL connection set up overview
9.1 Principle of operations
The SHDSL switch called STU-C is in charge of setting the connection
When two shdsl switches are connected through a twisted pair, one has the function to initiate the
connection, to analyse the connection quality, and to negotiate the data rate; the other SHDSL switch
can only accept.
The SHDSL switch which initiates the connection is called the STU-C, while the one which accepts the
connection is called the STU-R switch.
The STU-C negotiates in order to obtain the selected SNR margin
When it connects, the STU-C switch measures the reception signal level and the noise level and
calculates the signal-to-noise ratio (SNR ratio).
The longer the distance and the higher the noise level over the line, the smaller the SNR ratio.
A minimum SNR is required to connect two SHDSL switches through a line at a given data rate.
The difference between the SNR ratio as it is measured and the minimum required is the SNR margin.
The greater the SNR margin, the more reliable the connection at a given data rate.
One can select the SNR margin; in that way, one selects the reliability of the connection.
The STU-C SHDSL switch negotiates with the STU-R switch; the data rate is decreased from the
maximum data rate, until the selected SNR margin is obtained.
To make the configuration simple, one does not select the SNR margin or such or such
technical parameter but only a connection profile including all the parameters of the
connection.
To configure an shdsl connection, one has only to assign one profile to each SHDSL port.
The Performance profile optimises the data rate up to 5,7 Mb/s.
The Standard profile is the advised compromise between the data rate and the reliability of the connection.
The Endurance profile optimises the reliability; the data rate which will be obtained is generally lower than with the
standard or the performance profile.
The Turbo-short profile can be used only over short distance (not more than 1 Km); it provides up to 10 Mb/s using a
proprietary modulation.