User's Manual

BCM450 System Start Up
NN40010-317 Issue 1.2 BCM450 Rls 6.0 55
 Secondary external: The DTM/BRI acts as a standby reference point.
If there are excessive errors on the Primary reference link, or the
DTM/BRI designated as Primary reference fails, the Secondary
DTM/BRI obtains the timing from the network to be used for system
synchronization. This is the default value for the second DTM in a
BCM. Private network: If this system is in a private network and is
intended to provide the Master clock for that private network, then there
should be no Secondary reference defined on any DTM/BRI. Note that
there should only be one defined Secondary clock source on a system.
 Internal: The DTM/BRI does not obtain timing from the network, but
transmits the internally-generated system timing, from the
Primary/Secondary source, to equipment to which it is connected. Note
that while in the absence of a DTM Primary clocking source a BRI
module can be used for the primary timing reference, it is always
recommended that, when possible, DTM(s) be used as primary (and
secondary) clock sources and that any remaining DTMs/BRIs be set to
Timing Master.