Network failure types
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<p>A network which contains many network components of both hardware and software can incur failures due to one (or even multiple) of its contained components incurs a failure. Ranging from the largest to the smallest and from hardware to software, network failures can be divided into the following categories:<br />
<li>Control plane failure:</b>this type of failure is mainly related to software, i.e., network control plane software. For example, in a GMPLS-based network which is made up of a control plane and data plane, the control plane failure would lose the control of the data plane, which means that we cannot establish new service connections, or terminate or modify an existing service connections within the data plane, even though the existing connections can still perform normally to carry user's data. In other type of networks such as IP networks, the control plane failure can be even more serious. For example, the pollution of IP lookup tables at some routers would cause all the IP traffic on these nodes difficult to be forwarded. Similar stories occur for viruses attacking IP routers. They disable the IP networks through disabling IP network control plane.</li>
<li>Subnetwork failure: </b>this is a type failure occurred with a regional subnetwork that commonly shares a risk, e.g., a region that has high occurring frequency of earthquake. In addition, some large disasters such as flooding, tsunami, etc. can also disable a regional subnetwork.</li>
<li>Node failure: </b>this is a type of failure occurred with a single network node. The reasons for this kind of failure include accidents or disasters at a network operational center, such as power shutdown due to fire, flooding, etc.</li>
<li>Network card failure: </b>network card failure is a type of failure under the umbrella of the node failure type. Rather than the shutdown of the whole switch node, sometimes a failure can occur only with a network interface card. For example, the failures or faults such as a laser outage, fault of a circuit board, or software bugs, etc. can also contribute to a network card failure.</li>
<li>Link failure: </b>link failure in general is the most common network failure that occurs due to fiber cut.</li>
<li><a href="http://www.network-protection.net/shared-risk-link-group-srlg/">SRLG</a> failure: </b>SRLG failure is a generic concept to define all types of network failures whenever a common SRLG incurs a failure. Here a SRLG can be a fiber link, node, subnetwork, or control plane, etc.</li>
<p>Single failure and multiple failures: in general network failure implies a single network failure because network failure normally seldom occurs. However, under some situations, there can be more than failure occurring with a network. This kind of situation is called multiple failure, example, dual failures and triple failures. For a network, planning for full recovery of multiple failures generally requires much high protection capacity than that of purely for a single failure.<br /></span>
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