Page 966 - 5G Basics - Core Network Aspects

2 Transport aspects

12.3.6 Alignment of initialization procedures of multiple joining lines (Informative)

The procedures and rules described in this clause do not concern interoperability between the FTU-O and
FTU-R, but are necessary to ensure vectored operation of joining lines, including FEXT cancellation and
minimum distortions in active lines during the joining of multiple lines.

In case multiple lines are joining to the vectored group, their initialization procedures should be aligned.
First, the line that completes the ITU-T G.994.1 handshake becomes a member of the joining group (joining
line) or a member of the waiting group (waiting line) using the rules presented in clause 12.3.6.1. Further,
the line proceeds depending on the group it has been assigned to as described in the following clauses.
12.3.6.1 Joining group and waiting group (Informative)

The FTU-O of the line that completes the ITU-T G.994.1 handshake, while in O-QUIET 1 stage, monitors the
status of the joining group. If the joining group gets open after FTU-O transitions into O-QUIET 1, the FTU-O
considers the line being in the joining group, and terminates the O-QUIET 1 stage, and continues
initialization procedure as defined in clause 12.3.2.
If the joining group is closed, the FTU-O is in the waiting group. The FTU-O stays in the waiting group and
goes back to ITU-T G.994.1 handshake after the CD_time_out_1 timeout is reached or by request of the VCE
(in case the VCE does not expect the joining group to open during a relevant time).

The FTU-R, after entering the QUIET 1 stage, attempts to receive the O-P-CHANNEL-DISCOVERY 1-1 signal. If
no reception of O-P-CHANNEL-DISCOVERY 1-1 signal occurs within CD_time_out_1 timeout after the start
of the QUIET 1 stage, the FTU-R goes back to the ITU-T G.994.1 handshake.

12.3.6.2 Alignment of the initialization procedures of multiple joining lines (Informative)
If the joining group contains multiple lines, initialization procedures of all joining lines are aligned, while
each FTU-O performs the initialization procedure with the peer FTU-R, as defined in clause 12.3.2. The
alignment includes at least the following rules:
1) The VCE controls the start and the end of O-P-VECTOR 1 signal transmission in all joining lines. This
is necessary to ensure that downstream FEXT into active lines is estimated when all joining lines
transmit simultaneously. It's also beneficial if transmission of O-VECTOR 1 stage ends in all lines
simultaneously.
2) If a special probe sequence is used, the VCE controls the entry to O-P-CHANNEL-DISCOVERY 1-1
signal of all joining lines. This is necessary to ensure that downstream direct channel of the joining
lines are properly estimated.
3) Transmission of O-P-SYNCHRO 1-1 signal is simultaneous in all joining lines. This is necessary to
synchronize IDS in all joining lines.

4) Transmission of O-P-SYNCHRO 1 signal is simultaneous in all joining lines. This is necessary to align
R-P-VECTOR 1 signals in all lines to ensure that upstream FEXT between all lines is estimated when
all joining lines transmit simultaneously.
5) Transmission of O-P-SYNCHRO 3 signal is simultaneous in all joining lines. This is necessary to align
R-P-VECTOR 1-1 signals in all lines and ensure that upstream FEXT between all lines is estimated
when all joining lines transmit simultaneously.

6) Transmission of O-P-SYNCHRO 4 signal is simultaneous in all joining lines. This is necessary to align
O-P-VECTOR 2 signals in all lines to ensure that downstream FEXT into joining lines is estimated
when all joining lines transmit simultaneously.
7) Transmission of O-P-SYNCHRO 4-1 signal is simultaneous in all joining lines. This is necessary to
align downstream PSD updates in all active and joining lines after VECTOR 2 stage.
12.3.6.3 Alignment of the parameters of multiple joining lines (Informative)

The VCE configures the following parameters for all joining lines:
1) A CE length that is equal to the value assigned for the active lines,

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