System Management
290
7210 SAS-M, T, R6, R12, Mxp, Sx, S Basic System
Configuration Guide
© 2021 Nokia.
Use subject to Terms available at: www.nokia.com
3HE 17358 AAAB TQZZA
Figure 28 PTP Slave Clock and Master Clock Synchronization Timing
Computation
When the IEEE 1588v2 standard is used for distribution of a frequency reference, the
slave calculates a message delay from the master to the slave based on the
timestamps exchanged. A sequence of these calculated delays contains information
about the relative frequencies of the master clock and slave clock, but also includes
a noise component related to the PDV experienced across the network. The slave
must filter the PDV effects to extract the relative frequency data and then adjust the
slave frequency to align with the master frequency.
When the IEEE 1588v2 standard is used for distribution of time, the 7210 SAS
calculates the offset between the 7210 SAS time base and the external master clock
time base based on the four timestamps exchanged. The 7210 SAS determines the
offset adjustment, and between these adjustments, it maintains the progression of
time using the frequency from the central clock of the node. This allows time to be
maintained using a Synchronous Ethernet input source even if the IEEE 1588v2
communications fail. When using IEEE 1588v2 for time distribution, the central clock
should, at a minimum, have the PTP input reference enabled.
Figure 29 shows the logical model for using PTP/1588 for network synchronization.
Master Slave
Sync
Follow_up (t1)
Delay_req
Delay_resp (t4)
38
40
42
44
46
48
50
52
54
56
58
60
62
40
42
44
46
48
50
52
54
56
58
60
62
64
O = Offset = Slave - Master
t1, t2, t3, t4 Are Measured Values
t2 - t1 = Delay + Offset = 51 - 44 = 7
t4 - t3 = Delay - Offset = 57 - 56 = 1
Delay = ((t2 - t1) + (t4 - t3))/2 = 4
Offset = ((t2 - t1) - (t4 - t3))/2 = 3
D = Delay
t1
t4
t2
OD
OSSG732
t3
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