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13 — System timing and timing sources
2902 MainStreet Technical Practices 13-7
May 2002 90-2906-01
Internal
For internal mode, the system uses its internal clock as its internal crystal oscillator.
The oscillator supplies a timing reference accurate to ±25 ppm. When synchronized
to this source, the timing is said to be free running.
Derived
For derived mode, an 8 kHz clock is derived from a primary rate link.
Procedure 13-5 To configure the type of synchronization
where
source number is 1 or 2
p is 1 or 2
13.4 Class number
Timing source selection is determined by class number. The class number is
configurable and provides a means for specifying the preference of a timing source:
the higher the preference, the lower the class number. For example, a timing source
assigned a class number of 1 is assigned the highest preference.
Class numbers can be assigned to timing sources and to nodes. When assigned to a
node, the class number refers to the internal clock of the node.
A class number of 15 indicates a source that does not normally supply network
timing. For example, internal synchronization (free run) is assigned a class number
of 15 so that it is the last source available.
Class numbers from 1 to 14 establish preferences among the possible timing sources
in the node or network. The node or network uses only at the class number to
determine the source hierarchy—in a network, there is no distinction between node
class numbers and timing source class numbers.
A node class number of 0 is generated by a node in standalone mode that may be
intimately linked with an ANS network but is not part of the ANS. Class 0 nodes
derive their timing from a source configured at the node. Class 0 nodes can only be
connected to the ANS network over inter-sector links. Class number 0 cannot be
user-configured.
DERIVED <P p >
↵
FREE_RUN
CONFIG — SYNCH — SRC_NUMBER — < source number >
↵
SOURCE
SK000475