Juniper JUNOSE 10.0.X PHYSICAL LAYER, Configuration Manual

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Bidirectional Switching Mode
In bidirectional switching mode, the router switches both ends of an APS pair to the
same working interface or to the same protect interface when either end determines
that a switch is required.
Possible reasons for initiating a bidirectional switch include:
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Detection of a signal failure
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Receipt of an “aps force” on page 95 or “aps manual” on page 96 from the local
end of an APS pair
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Reversion to the working interface after a failure has been corrected and the
timeout value specified in “aps revert” on page 93 has expired
The devices at both the local and remote ends of an APS pair must support
bidirectional switching for the router to implement bidirectional switching mode.
Otherwise, the router implements unidirectional switching mode at both ends of the
APS pair.
The router detects support for bidirectional switching by interpreting the values of
the K1 and K2 bytes in the SONET/SDH frame. For details about the meanings of
the values of K1 and K2 bytes, see “Communication Methods” on page 75.
Unidirectional Switching Mode
In unidirectional switching mode, the router switches only one end of an APS pair
to the working interface or to the protect interface when that end determines that a
switch is required. Possible reasons for initiating a unidirectional switch are the same
as those described in “Bidirectional Switching Mode” on page 75 for initiating a
bidirectional switch.
Reversion After Switchover
A failed interface automatically reverts from the protect interface to the working
interface after the router detects that the working interface is operational and the
timeout value specified in “aps revert” on page 93 has expired. Reversion applies
only to recovery from failures.
You can configure the router to revert to the working interface at a specified time
after it recovers. This feature enables you to use the protect interface as a redundant
connection that functions only when the working interface is not available.
Communication Methods
The router communicates with the remote device by using the K1 and K2 bytes in
the line overhead of the SONET/SDH frame. The values of these bytes determine the
switching and protect actions. Table 8 on page 76 and Table 9 on page 76 list the
meanings of the values of the K1 and K2 bytes. The bytes are defined in Telcordia
document GR-253—Synchronous Optical Network (SONET) Transport Systems:
Common Generic Criteria, Revision 3 (September 2000). See requirement objects
Overview
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Chapter 3: Configuring Unchannelized OCx/STMx Interfaces