Page 1001 - 5G Basics - Core Network Aspects

Transport aspects 2

• SNRM ≥ L2_TARSNRM for all active data subcarriers.

• SNRM_RMC ≥ TARSNRM-RMC for all RMC subcarriers.
Within the above constraints, the FTU-O and VCE shall jointly select the values in the L2.2-Entry-Request
eoc command:
While keeping same PSD, set of data subcarriers and set of RMC subcarriers as in L2.1, the FTU-O and
VCE jointly determine via a vendor discretionary method:
– the upstream bit loading table and framing parameters
– the proposed downstream bit loading table
– the value of X (the time interval between two adjacent downstream RMC symbols represented as
a number of superframes see clause 13.4.2.1)
Within the above constraints, for downstream, the FTU-R in the L2.2-Entry-Confirm eoc response shall
select a bit loading table as close as possible to the proposed bit loading table in the L2.2-Entry-Request eoc
command.
NOTE 1 – The above policy allows a vendor discretionary compromise between robustness and power saving.
NOTE 2 – There is no change of transmit PSD.
At the transition from L2.1B to L2.2, synchronization of DTUs with RMC symbols defined in clause 13.4.2.1
shall not cause uncorrectable DTUs.
NOTE 3 – Uncorrectable DTUs during the transition from L2.1B to L2.2 may be avoided by sending only dummy DTUs
prior to the transition.
13.4.2.3 Operation during L2.2

13.4.2.3.1 L2.2 operation policy
During operation in L2.2, the constraints defined in clause 13.4.2.2 shall apply, except for the SNR margin
constraints which shall satisfy:
• SNRM ≥ MINSNRM for all active data subcarriers
• SNRM_RMC ≥ MINSNRM-RMC for all RMC subcarriers

13.4.2.3.2 L2.2 operation procedures
If during L2.2 any of the L2.2 constraints are not met, the FTU-O ME in coordination with the VCE shall raise
an L2.2_constraints anomaly. Upon an L2.2_constraints anomaly occurring, the DRA may send a
LinkState.Request primitive to exit from the L2.2 link state to the L2.1B link state, as defined in clause
12.1.1.6. The DRA may also send a LinkState.Request primitive to transition from the L2.2 link state to the
L2.1N link state when the FTU-R is no longer operating with battery power. The transition shall be initiated
by the FTU-O using the L2.2 exit procedure defined in clause 13.4.2.4. No OLR procedures shall be used
during L2.2.

NOTE – Since no OLR procedures are defined for use during L2.2, the way to fix performance issues during L2.2 is by
transition into L2.1. In L2.1 the upstream and downstream transmission parameters are modified appropriately, and
the link, upon request from the DRA, goes back to L2.2 with updated RMC transmission schedule or other relevant
L2.2 parameters using the procedure defined in clause 13.4.2.1.

Fast retrain shall be applied according to the fast retrain policy L2.2_FRpolicy = 0 (see clause 12.1.4.2).
13.4.2.4 L2.2 Exit procedure

13.4.2.4.1 Procedures at exit of L2.2
The procedure defined in this clause shall be used to transition from the L2.2 link state to the L2.1N or
L2.1B link state. Transition from the L2.2 link state to the L2.1N or L2.1B link state shall be initiated by the
FTU-O. Upon reception of the LinkState.request (L2.1N or L2.1B) primitive across the γ-O interface (see
Table 8-3), the FTU-O shall send to the FTU-R an L2.2-Exit-Request eoc command (see clause 11.2.2.16).

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