Maintenance Manual

Chapter 5 General Administration
ICM Time Synchronization
5-16
Cisco ICM Enterprise Edition Administrator Guide Release 6.0(0)
The disabled Synchronizer receives time messages from the enabled Synchronizer
every half second, and periodically compares the received time to the system time.
In the event of a discrepancy greater than 100 milliseconds, the disabled
Synchronizer uses system calls to run the system clock 10% faster or slower (as
needed) until the discrepancy falls within tolerance. The net effect is that the
systems clock on the disabled side smoothly tracks the MDS time, which in turn
smoothly tracks the system clock on the enabled side.
MDS provides a “Set System Time” message API for setting the time. When MDS
receives this message, the enabled Synchronizer sets the system time and the
disabled Synchronizer does nothing (since it will track the clock of the enabled
side). The “Set System Time” message should be sent by a synchronous process
(on both sides of the system), since it cannot be determined which Synchronizer
is the enabled one.
VRU PIM
The VRU PIM supports a mechanism for keeping the VRU time synchronized
with ICM time. The PIM periodically compares the time reported by the VRU to
its own time, and sends a time adjustment message to the VRU if the times differ
by more than about 15 seconds.
Router
The Router attempts to keep the clocks of all controllers (NICs and PGs)
synchronized with its own MDS time. It periodically queries each controller for
its time. If the time discrepancy between the Router and controller is sufficiently
large (15 seconds or more), the Router sends a time adjustment message to the
controller instructing it to adjust its time by a delta value. The Router uses the
round-trip delay of the query-response to account for transmission delay when
computing the time adjustment.
Different controllers handle the time adjustment message in different ways. On a
PG, OPC uses the MDS API to adjust the time of the (possibly duplexed) PG. A
NIC ignores the time adjustment message, since adjusting the time on the Router
machine could have unwanted feedback effects.
The Router records the time skew of all controllers and peripherals and can report
these statistics via rttest.