Link protection

A single fiber cut can lead to heavy losses of traffic and protection-switching techniques have been used as the key source to ensure survivability in networks.

These nodes detect the fault responsible to initiate the protection mechanisms in order to detour the affected traffic from the failed link onto predetermined reserved paths.

When the WDM layer was created, the optical networks survivability techniques in consideration were mainly based on many elements of SONET protection in order to ensure maximum compatibility with the legacy systems (SONET systems).

[3] An example of a link-based protection architecture at the Optical Transport Network layer is a Bidirectional Line Switched Ring (BLSR).

Four-fiber BLSRs use two types of protection mechanisms during failure recovery, namely ring and span switching.

In span switching, when the source or destination on a link fails, traffic gets routed onto the protection fiber between the two nodes on the same link and when a fiber or cable cut occurs, service is restored using the ring switching mechanism.

[1] The techniques mentioned above for SONET and WDM networks can also be applied to mesh network architectures provided there are ring decompositions for the mesh architectures; and use well defined protection-switching schemes to restore service when a failure occurs.

This technique was initially proposed to remove the additional redundancy issue caused by the ring cover scheme.

By doing this, p-cycles reduce the redundancy required to protect a mesh network against link failure.

One of the best features of p-cycles is its ability to allow savings in spare resources and they are also recognized to be the most efficient protection structures as for capacity minimization.

In recent years, packet based networks made a big leap and almost every single service provided (voice, IP-TV, etc.)

[6] In this protection, an LSP tunnel is set up through the network to provide a backup for a vulnerable physical link.