Solutions
Optical Bypass Protection Switching Solutions
In some network topologies, failure of network equipment or power outages may have an impact not only on traffic that terminates at these nodes but also on the rest of the network. The most effective solution for such scenarios are Bypass systems that allow traffic to bypass failed nodes.
Figure 1 depicts a typical linear (chain) network in which a failed node can cause failure in of most of the network. The deployed bypass system provides a solution to such outages.
Figure 1 depicts a typical linear (chain) network in which a failed node can cause failure in of most of the network. The deployed bypass system provides a solution to such outages.
Figure 1: Linear (chain) network
While the need for bypass protection is intuitive in linear networks, other topologies may benefit from it as well. One case is ring networks, whose self-healing capacity is limited to a single failure. A ring-topology network can recover from a single fiber cut or failure of a single node: traffic terminated at a failed node is lost, but the rest of the network continues to function. In some cases, such as metro networks that are subject to floods and power outages, multiple concurrent failures are likely and the ring’s inherent resilience is insufficient. Using a bypass switch at each node offers protection from multiple failures, bypassing all of the failed nodes so even in multi-node failure situation the ring will maintain its self-healing operation. Figure 2 shows how bypass systems can protect a ring from multiple failures.
Figure 2: Ring network
Several network engineering rules must be followed in designing such a deployment:
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Many nodes regenerate the optical signal. When nodes are bypassed, the signal is no longer regenerated at the point of failure. The power budget at this point must suffice to reach the next functional node.
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The network’s connection management is responsible for avoiding misconnections.
In case of node failures due to power outage a bypass system must provide three basic features:
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When power is down the optical switches must switch automatically to bypass connectivity
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Traffic must be transferred via the switch even when power is down
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When power returns the optical switches must switch back to normal connectivity
