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Transport aspects 2

Table 12-19 – FTU-R MS message NPar(3) bit definitions

ITU-T G.994.1 SPar(2) bit Definition of NPar(3) bits
CD time out 2 This 3-bit field shall be coded as an unsigned integer n=0 to 7, indicating that the
CD_time_out_2 value that shall be used by both the FTU-O and FTU-R equals (n+1)
times ten seconds. The CD_time_out_2 value indicated shall not exceed the lowest of
the maximum CD_time_out_2 values indicated in the last previous CLR and the last
previous CL message.
NOTE – The maximum CD_time_out_2 value indicated in the CLR message is the highest valid
value and hence implies no bound on the value indicated in the MS message.
12.3.3 Channel discovery phase

12.3.3.1 Overview
The channel discovery phase is the first phase when the ITU-T G.9701 signals are exchanged between FTUs.
The following tasks are completed during the channel discovery phase:
Cancelling FEXT from joining lines into active lines
• Timing recovery and selection of pilot tone(s);

• Establishing communication between the FTU-O and FTU-R over the SOC;
• Exchange information necessary to set up and adjust modulation parameters (transmit PSD,
window length, timing advance and others)

• Selection of blackout subcarriers
• Cancelling FEXT into joining lines
• Setting up optimized PSDs for both transmission directions

The channel discovery phase consists of several stages, all described in the following clauses.
The following convention is used for the naming of stages of initialization and initialization signals:
– Stages of initialization are named XXX or O-XXX or R-XXX (e.g., O-VECTOR 1)
– Initialization signals are named O-P-XXX or R-P-XXX (e.g., O-P-VECTOR 1)

To synchronize different stages of the procedure (i.e., get stages of the initialization synchronously initiated
and terminated at both FTU-O and FTU-R), FTU-O sends O-P-SYNCHRO signals. The content of the
O-P-SYNCHRO signals is defined in clauses 12.3.3.3 and 12.3.4.3 (for O-P-SYNCHRO 6).
Figure 12-8 shows the details of the early stages of channel discovery phase, specifically the CHANNEL
DISCOVERY 1-1 and CHANNEL DISCOVERY 1 stages.

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