Page 834 - 5G Basics - Core Network Aspects

2 Transport aspects

The bytes for the superframe count of time stamps ToD(t1) and ToD(t4) contain the superframe count when
ToD(t1) and ToD(t4) are taken by the FTU-O (i.e., at the t1 and t4 event, see Figure 8-13). This value shall be a
multiple of 16. The time synchronization update period indicates to the FTU-R at which superframe count
the next set of ToD(t1), ToD(t2), ToD(t3), and ToD(t4) time stamps shall be recorded. The time
synchronization update period (in superframes) shall be a multiple of 16 and shall not exceed the value of
TSP that is set during initialization (see Table 12-42).
The ToD(t1) and ToD(t4) time stamps shall represent the time offset between the current time of the RTC-O
(i.e., the time elapsed since the epoch) at the t1 and t4 events respectively. The ToD(t2) and ToD(t3)
timestamps shall represent the time of the RTC-R (i.e., the time elapsed since the epoch) at the t2 and t3
events respectively. The FTU-R shall use the same epoch as the FTU-O, where this common epoch is set by
the TCE and passed to the ToD-O over the O reference point (by the ToD_mc_value).
NOTE – If at the t1 event the RTC-O shows +2.000000001 seconds have elapsed since the epoch, this is represented in
the ToD(t1) timestamp by seconds = 0x0000 0000 0002 and nanoseconds = 0x0000 0001. The epoch may be locally set
at the DPU or may be an absolute instant in time. For example, if the epoch is the PTP epoch, this means that
time-of-day = 1 January 1970 00:00:02.000000001.

Table 11-27 – Time synchronization responses sent by the FTU-R
Length
Name Byte Content
(bytes)
ACK 24 2 8116 (Note 1)
(ToD(t2) 3 and 4 Two bytes for the superframe count of the ToD(t2) and ToD(t3)
ToD(t3) time stamps.
Timestamps) 5 to 10 Six bytes describing the integer portion of the ToD(t2)
timestamp in units of seconds.
11 to 14 Four bytes describing the fractional portion of the ToD(t2)
timestamp in units of nanoseconds. (Note 2)

15 to 20 Six bytes describing the integer portion of the ToD(t3)
timestamp in units of seconds.
21 to 24 Four bytes describing the fractional portion of the ToD(t3)
timestamp in units of nanoseconds. (Note 2)

Reject 3 2 8216 (Note 1)
1 One byte for reason code (see Table 11-28)
NOTE 1 – All other values for byte 2 are reserved by ITU-T.
9
NOTE 2 – The nanosecond portion is always less than 10 .

Table 11-28 – Reason codes for time synchronization response

Reason Byte value

Busy 0116
Invalid parameters 0216
t2 and t3 timestamps no longer available at the FTU-R 0316
Still acquiring ToD frequency synchronization 0416
NOTE – All other reason codes are reserved by ITU-T.

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