Page 920 - 5G Basics - Core Network Aspects

2 Transport aspects

The SOC is active in both upstream and downstream; at the start of the stage both FTU-O and FTU-R
transmits O-IDLE and R-IDLE, respectively. After transmission of R-IDLE, the FTU-R transmits R-MSG 1
message that, besides other parameters, communicates to the FTU-O the local estimate of the electrical
length, and other relevant parameters (see clause 12.3.3.2). The FTU-O acknowledges the reception of
R-MSG 1 message by transmitting an O-UPDATE message that determines the final value of the electrical
length, the final correction of time gap Tg1', and the upstream PSD adjustments (see clause 12.3.3.2.4). The
FTU-R acknowledges reception of O-UPDATE message by sending a R-UPDATE message and continues
transmission of R-IDLE until the end of the stage.

The FTU-O determines the duration of the CHANNEL DISCOVERY 2 stage and signals the completion of this
stage by sending an O-P-SYNCHRO 2 signal.

12.3.3.1.6 R-VECTOR 1.1 stage
During R-VECTOR 1.1 stage the FTU-O continues transmission of sync symbols and O-IDLE over the SOC
channel. The FTU-R transmits only sync symbols modulated by probe sequence using the updated values of
the time gap Tg1' and updated values of the transmit PSD, based on the information received from the FTU-
O in the O-UPDATE message.

NOTE – During this stage, the VCE may repeat the procedures used during the R-VECTOR 1 stage to accommodate a
new value of Tg1' and upstream PSD, and:
– may estimate crosstalk between all active and all joining lines;
– may compute updates of post-canceller coefficients.
At the end of the stage, post-canceller coefficients, FEQ gains and bit loading (except joining lines) are
updated for all active and joining lines.

The FTU-O determines the duration of the R-VECTOR 1.1 stage and signals the completion of this stage by
sending an O-P-SYNCHRO 3 signal.

12.3.3.1.7 VECTOR 2 stage
The FTU-O continues transmission of sync symbols modulated by probe sequence and SOC symbols over
the first sds symbol positions of each downstream logical frame. The SOC is active; the FTU-O first transmits
O-IDLE and then FTU-O transmits the O-VECTOR-FEEDBACK message that communicates to the FTU-R the
requested parameters of the VF sample report and the new upstream SOC tone repetition rate.

The FTU-R transmits sync symbols modulated by the probe sequence and SOC symbols over the first sus
symbol positions in each upstream logical frame (see field 19 of O-SIGNATURE message in Table 12-20 in
clause 12.3.3.2.1). The SOC is active; the FTU-R first transmits R-IDLE, and upon reception of
O-VECTOR-FEEDBACK message, the FTU-R sends an R-ACK message to indicate correct reception of the
message. Upon reception of the R-ACK message, the FTU-O transmits an O-P-SYNCHRO 3-1 signal. Upon
reception of the O-P-SYNCHRO-3-1 signal, the FTU-R starts transmission of a sequence of R-VECTOR-
FEEDBACK messages containing either clipped error samples or DFT output samples with parameters as
requested by the FTU-O and with the SOC modulation using the requested upstream SOC tone repetition
rate.
NOTE – By using the vectoring feedback, the VCE may estimate downstream crosstalk from the active lines into the
joining lines and between joining lines, and computes precoder coefficients to cancel the crosstalk from active lines
into the joining lines and between joining lines. Based on the computed precoder coefficients, the VCE may compute
for all lines PSD updates, new gains and new bit loading for active lines (if required).
At the end of the stage, the VCE applies precoder coefficients and PSD updates to all active and joining
lines.

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