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Cisco SCE8000 GBE Installation and Configuration Guide
Chapter 3 Cisco SCE 8000 Topology and Topology-Related Parameters
Link Continuity
Link Continuity
The internal bypass mechanism of the Cisco SCE 8000 allows traffic to continue to flow, if desired, even
if the device itself is not fully functioning. In addition, the Cisco SCE 8000 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.
When the Cisco SCE 8000 is connected to the network through an optical splitter, a failure of the Cisco
SCE 8000 does not affect the traffic flow, as the traffic continues to flow through the optical splitter.
• Internal Bypass Mechanism, page 3-11
• External Optical Bypass, page 3-11
Internal Bypass Mechanism
The Cisco SCE 8000-SIP module includes a bypass mechanism that is enabled upon Cisco SCE 8000
failure.
The Cisco SCE 8000-SIP supports the following three modes:
• 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 SCE 8000 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).
The SPA Interface Processor card cannot preserve the link in the following circumstances:
• During platform reboot (SW reload), there is an 11-second period during which the link is forced
down (cutoff functionality). If any routing or spanning tree protocols are used in the network, this
delay may be extended.
• During a power failure (The Cisco SCE 8000 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.
External Optical Bypass
When a separate bypass mechanism is required, 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
SCE 8000 chassis or be rack-mounted externally. The external optical bypass device can also be
controlled manually by specific CLI commands.
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