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2 Transport aspects

10.3.2.5 Identification of the VFRB

10.3.2.5.1 Frequency identification control parameters
Frequency identification allows to reduce the size of the VFRB and to fit the corresponding eoc or SOC
message into the desired number of superframe periods (usually one superframe) by reducing the number
of reported VF samples. Frequency identification is defined by two parameters:
• the frequency sub-sampling factor (F_sub);
• the frequency shift step (s).

Frequency identification is enabled by setting s ≠ 0.
With sub-sampling rate of F_sub, VF samples for a particular element X of the probe sequence are reported
only for subcarriers of the given vectored band with indices:
i = imin + (s×(n-1))MOD(F_sub) + j×F_sub

where:
imin is the lowest index of the vectored band;
j = 0, 1, 2…
n is a count of probe sequence cycles covered by the reports; for the first report, n=1.
For example, if F_sub = 4, at the first probe sequence cycle (n=1) all subcarriers with indices imin+j×4, j = 0, 1,
2… will be reported until the upper index of the vectored band. At the second probe sequence cycle (n=2),
the starting subcarrier index is increased by s. If s = 2, all subcarriers with indices imin+2+j×4 will be reported
at the second probe sequence cycle. These two reports will provide one set of VF samples equivalent to a
single report with F_sub = 2 (no more reports are required because in the next probe sequence cycle (n=3)
the subcarriers with indices imin+j×4, j = 0, 1, 2… will be reported again).
The valid values of frequency identification control parameters are presented in Table 10-11.

Table 10-11 – Valid values of frequency identification control parameters

Parameter Valid values for VCE Mandatory values for FTU-R to support

F_sub As per Table 10-10 All valid values.
s 1, 2, 3, 4 provided that s < F_sub (Note) All valid values.
NOTE – s = 0 is a special value indicating that frequency identification is disabled.
For frequency identification reporting:
– To start vectoring feedback reporting, the value of parameter q shall be set to 1.

– To stop vectoring feedback reporting, the value of parameter q shall be set to 0.
10.3.2.5.2 Time identification control parameters

On each of the sync symbols indicated by the FTU-O by the associated superframe count, the FTU-R shall
transmit a single VFRB. In each VFRB, the FTU-R shall also include the superframe count (as defined in
clause 12.3.3.2.6) as identification of the downstream sync symbol the VFRB corresponds to. The FTU-O
shall indicate such superframe counts using the following time identification control parameters:
• the VFRB update period (q);
• the VFRB shift period (z).
Time identification is enabled by setting s = 0.

The FTU-R shall send the first VFRB on the first sync symbol following the reception of the request to
update the VFRB control parameters. Then it shall send a VFRB on every q-th subsequent sync symbol
position z-1 times. After z VFRBs are sent (which takes q×z superframes), the next VFRB shall be reported

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