Etic Telecom XLAN+ Series, Setup Manual

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SETUP
DOC_DEV_XS_Setup guide_C
page 13
2 SHDSL connection set up overview
2.1 Principle of operation
When two XS switches are connected by a twisted pair, one switch initiates the connection while the other
responds and adapts automatically its data rate.
The switch that initiates the connection is called STU-C.
The switch that responds and adapts is called STU-R.
Thus a line is always connected on one side to a switch acting as the STU-C and on the other side to a
switch acting as the STU-R.
One switch is normally configured as a STU-C and the other as a STU-R. However, to make the configuration
simpler, the switch configured as a STU-C is able to automatically change to STU-R mode if it detects the
presence of a STU-C on the remote side. Thus, two XS configured both in STU-C will find a way to connect.
One of the two will switch to STU-R.
The STU-C initiates the connection and measure the received signal level and the noise level and calculates
the signal to noise 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.
1 twisted pair
The STU-C switch
negociates the data
rate The STU-R switch
automatically adapts
STU-C STU-R