Link Continuity; Internal Bypass Mechanism; External Optical Bypass - Cisco SCE8000 Installation And Configuration Manual

Chapter 3 Cisco SCE8000 Topology and Topology-Related Parameters

Link Continuity

The internal bypass mechanism of the Cisco SCE8000 allows traffic to continue to flow, if desired, even
if the device itself is not fully functioning. In addition, the Cisco SCE8000 is designed with the ability
to control up to two external optical bypass devices (one per link). This is needed because the internal
bypass mechanism cannot maintain traffic flow in all cases.
Note that when the Cisco SCE8000 is connected to the network through an optical splitter, a failure of
the Cisco SCE8000 does not affect the traffic flow, as the traffic continues to flow through the optical
splitter.
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Internal Bypass Mechanism

The Cisco SCE8000 includes a SPA Interface Processor module with a bypass mechanism that is enabled
upon Cisco SCE8000 failure.
The SPA Interface Processor card supports the following three modes:
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The SPA Interface Processor card cannot preserve the link in the following circumstances:
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External Optical Bypass

In installations in which the limitations of the internal bypass are not acceptable, an external optical
bypass device can be used to provide dependable link continuity. The external optical bypass device can
be installed either inside the Cisco SCE8000 chassis or be rack-mounted externally. The external optical
bypass device can also be controlled manually by specific CLI commands.
Under normal operating conditions, traffic flows through the link as usual, with the exception that the
optical bypass module sits on the link.
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Internal Bypass Mechanism, page 3-9
External Optical Bypass, page 3-9
Bypass — The bypass mechanism preserves the network link, but traffic is not processed for
monitoring or for control.
Forwarding — This is the normal operational mode, in which the Cisco SCE8000 processes the
traffic for monitoring and control purposes.
Cutoff — There is no forwarding of traffic, and the physical link is forced down (cutoff
functionality at layer 1).
During platform reboot (SW reload), there is a 5-second period (at most) during which the link is
forced down (cutoff functionality).
During a power failure (The Cisco SCE8000 has two power supplies. A power failure occurs only
when both of them fail).
Under certain types of failure within the SIP module, the SPA cards, or the XFP optic modules.
Cisco SCE8000 Installation and Configuration Guide, Rel 3.1.7
Link Continuity
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