Control, Transmission, and Synchronization Interfaces
Issue 8.0 July 2002
5-43
Summary of Timing Rules for Bidirectional Line-Switched
Rings 5
Strategy 1
Strategy 1 is applicable for all ring topologies.
â– At least one node must be externally timed from a stratum 1 traceable
timing source that is not distributed by this ring.
â– Nodes used as a timing drop must be through timed.
â– Other nodes may be externally timed or through timed.
Strategy 2
Strategy 2 is applicable for rings that are used to distribute timing and where there
is a BITS clock at every node. These are typically rings that connect central
offices.
Externally timed nodes that are used to derive timing must obey the following
rules to guarantee no timing loops:
â– All nodes must be provisioned externally timed.
â– At least one node must be timed from a stratum 1 traceable timing source
that is not derived from this ring.
â– Use only the Timing Out 1 signal. Alternately, it is possible to use only the
Timing Out 2 signal—conditional that Timing Out 1 is not used.
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