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2                                                 Transport aspects


            TPS_TESTMODE command, the FTU-R shall acknowledge it with an ACK response. Afterwards, the FTU-R
            shall set TPS_TESTMODE enabled. Upon reception of the leave TPS_TESTMODE command, the FTU-R shall
            set TPS_TESTMODE disabled. The generation of DTUs is as specified in clause 8.3.1.
            11.2.2.7     NTR frequency synchronization command

            If  NTR  transport  is  enabled  during  the  initialization,  NTR  frequency  synchronization  eoc  commands
            (presented in Table 11-24) shall be sent by the FTU-O and used by the FTU-R to facilitate NTR frequency
            synchronization as described in clause 8.4.1. If NTR transport is disabled during the initialization, the FTU-O
            shall not send NTR synchronization commands during the showtime.
            The FTU-R shall not send a response to the NTR synchronization command.

            The  NTR  frequency  synchronization  command  is  a  near-high  priority  command.  The  first  byte  of  the
            command shall be the command type assigned as shown in Table 11-4 (NTR frequency synchronization
            command). The remaining bytes of the command shall be as specified in Table 11-24.

            The FTU-O shall always send the most recent NTR frequency synchronization command and shall discard all
            older NTR frequency synchronization commands.
            NOTE  –  Since  no  response  is  defined,  the  FTU-O  management  entity  will  not  retransmit  the  lost  NTR  frequency
            synchronization command.


                          Table 11-24 – NTR frequency synchronization command (sent by the FTU-O)

                                     Length
                    Name                           Byte                          Content
                                     (bytes)
             NTR phase offset          6            2       0116 (Note 1)
                                                  3 and 4   Two bytes for the count of the superframe associated
                                                            with the event (Note 2).
                                                  5 and 6   Two bytes, representing the NTR phase offset value (φ) as
                                                            defined in clause 8.4.1.1.
             NOTE 1 – All other values for byte 2 are reserved by ITU-T.
             NOTE 2 – The value shall be even.
            If  the  FTU-O  indicates  during  the  initialization  that  its  PMD  sampling  frequency  is  locked  to  NTR,  as
            described in clause 8.4.1, the NTR synchronization command shall not be sent by the FTU-O and shall be
            ignored by the FTU-R.

            11.2.2.8   ToD frequency synchronization command

            The ToD frequency synchronization command shall only be used in one direction, from FTU-O to FTU-R. The
            FTU-R  shall  not  send  a  response  to  a  ToD  frequency  synchronization  command.  The  ToD  frequency
            synchronization command shall be used if frequency synchronization using ToD phase difference is selected
            during  the  initialization;  if  frequency  synchronization  through  locking  the  PMD  sample  clock  is  selected
            during the initialization, the ToD frequency synchronization command shall not be used (see clause 8.5.2).

            The  ToD  frequency  synchronization  command  is  a  near-high  priority  command.  The  first  byte  of  the
            command  shall  be  the  command  type  assigned  as shown  in  Table  11-4  (ToD  frequency  synchronization
            command). The remaining bytes of the command shall be as specified in Table 11-25.
            The  ToD  phase  difference  value  and  corresponding  t1  event  number  shall  be  encapsulated  in  a  ToD
            frequency synchronization command using the format defined in clause 8.5.2.1 as follows:












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