Nokia 7210 SAS-M - 6.5.8.2 Performance Considerations

7210 SAS-M, T, R6, R12, Mxp, Sx, S Basic System
Configuration Guide
System Management
Edition: 01 3HE 16132 AAAB TQZZA 289
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.
Figure 29 Logical Model for Using PTP/1588 for Network Synchronization on 7210 SAS
Platforms
6.5.8.2 Performance Considerations
Although IEEE 1588v2 can be used on a network that is not PTP-aware, the use of
PTP-aware network elements (boundary clocks) within the packet switched network
improves synchronization performance by reducing the impact of PDV between the
grand master clock and the slave clock. In particular, when IEEE 1588v2 is used to
distribute high-accuracy time, such as for mobile base station phase requirements,
the network architecture requires the deployment of PTP awareness in every device
between the grandmaster and the mobile base station slave.
sw0455
Central Clock
Time Module
Central Clock
Frequency
Module (EEC)
1588 Master
Ports
1588 Slave
Ports
1588
messages
1588
messages
TO to ports
Nodal reference (TO)
ref1Frequency
recovered
from 1588
message
exchange
ref1 & ref2
allowed
only in PTP
hybrid mode
ref2
ptp
Periodic Time
offset calculated
from 1588 message
exchange
Timestamps
based on central
clock frequency
and offset