Figure 18: Ptp Slave Clock And Master Clock Synchronization - Alcatel-Lucent 7210 SAS M Configuration Manual

System Basics Introduction
When using IEEE 1588v2 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 will contain information of the relative frequencies of the master clock and slave
clock but will have noise component related to the packet delay variation (PDV) experienced
across the network. The slave must filter the PDV effects so as to extract the relative frequency
data and then adjust the slave frequency to align with the master frequency.
When using IEEE 1588v2 for distribution of time, the 7210 SAS uses the four timestamps
exchanged using the IEEE 1588v2 messages to determine the offset between the 7210 SAS time
base and the external master clock time base. The 7210 SAS determines the offset adjustment and
then in 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.
Page 232
Master
38
40
42
1 t 4 4
46
48
Follow_up (t1)
50
52
54
Delay_req
56
t2
58
60
Delay_resp (t4)
62

Figure 18: PTP Slave Clock and Master Clock Synchronization

Timing Computation
7210 SAS M, T, X, R6 Basic System Configuration Guide
Slave
40
42
44
46
48
Sync
50
t2
52
54
56 t3
58
O D
60
62
64
O = Offset = Slave - Master
D = Delay
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
OSSG644