Page 992 - 5G Basics - Core Network Aspects
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2                                                 Transport aspects


            2)      Reduce the PSD to achieve SNRM ≤ L2.1_MAXSNRM within the constraint PSD reduction L2_PSDR
                    ≤ L2_PSDR_max.

            Within the above constraints, for downstream, the FTU-O and VCE shall jointly select the values in the L2.1-
            Entry-Request eoc command so as to optimize in the priority specified:
            1)      While keeping same PSD as in L0, the FTU-O determines via a vendor discretionary method

                    –   the set of L2.1 subcarriers
                    –   the proposed bit loading table
                    –   the number of RMC symbols per superframe (N)
            2)      Reduce the PSD to achieve SNRM ≤ L2.1_MAXSNRM within the constraint PSD reduction L2_PSDR
                    ≤ L2_PSDR_max.
            Within the above constraints, for downstream, the FTU-R shall select the bit loading table and the framing
            parameters values in the L2.1-Entry-Confirm eoc response so as to minimize the bit loading.
            NOTE 2 – The above policy allows a vendor discretionary compromise between robustness and power saving.
            13.4.1.3   Operation during L2.1

            At the entry into an L2.1 link state, FTUs apply the RMC transmission schedule and transmission parameters
            and  framing  parameters  determined  during  the  L2.1  entry  procedure,  as  defined  in  clause 13.4.1.2.1.
            During  an  L2.1  link  state,  the  RMC  schedule  and  transmission/framing  parameters  of  the  FTUs  may  be
            updated using appropriate OLR procedure.

            13.4.1.3.1  L2.1 operation policy
            The  method  used  by  the  transceivers  to  select  the  updated  values  of  RMC  transmission  schedule,
            transmission  and  framing  parameters  described  in  this  clause  is  vendor  discretionary.  However,  the
            selected values shall meet all of the following constraints.

            For the settings of L2.1 upstream RMC transmission schedule and transmission parameters:
            •       L2.1_ETR ≥ L2.1_ETR_min_eoc;
            •       L2.1_NDR ≤ L2.1_NDR_max;
            •       L2.1_Exit_ETR ≥ L2.1_Exit_ETR_min;

            For the settings of L2.1 downstream RMC transmission schedule and transmission parameters:
            •       L2.1_ETR ≥ L2.1_ETR_min_eoc;
            •       L2.1_NDR ≤ L2.1_NDR_max;
            •       L2.1_Exit_ETR ≥ L2.1_Exit_ETR_min;

            •       bi values shall be not greater than the bi values proposed in the L2.1-Entry-Request eoc command,
                    unless they are modified through a following TIGA procedure;
            •       BDR ≥ L2.1_BDR_min.

            For both the upstream and downstream transmission parameters:
            •       DTU size restriction:

                                                NDTU + Q × RFEC ≤ (N-1) × BDR,
                    where N is the number of active TDD frames per superframe in L2.1 (see clause 13.4.1.1).
            NOTE – This requirement on the L2.1 framing parameters implies the one-way latency without retransmission in the
            L2.1 link state does not exceed the duration of 1 superframe (TSF).
            •       Impulse noise protection:

                    •   at  least  against  a  combined  threat  of  worst-case  REIN  impulses  as  described  by  the
                        retransmission control parameters INP_min_rein and iat_rein_flag and of worst-case SHINE
                        impulses as described by the retransmission control parameter INP_min_shine, and



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