Path protection

Finding paths with protection, especially in elastic optical networks, was considered a difficult problem, but an efficient and optimal algorithm was proposed.

Since the optics along both paths are already active, DBPP is the fastest protection scheme available, usually in the order of a few tens of milliseconds, because there is no signaling involved in between ingress and egress nodes thus only needing the egress node to detect the failure and switch the traffic over to the unaffected path.

Being the fastest protection scheme also makes it the most expensive; normally using more than double of the provisioned capacity for the primary because the backup path is usually longer due to the link and/or node diversity rule of thumb.

However, in today’s Optical Mesh Network it can be used as a re-provisioning technique to help recover a second failure when the backup resources are already in use.

Even though the backup path is calculated, it is not assigned to a specific circuit before a failure occurs; cross connect requests are initiated after the fact on a first-come, first-served basis.

This technique is the simplest and fastest of all, but as it reserves and transmits packets on both LSP, it takes away bandwidth that could be shared and used by other LSPs.

In this protection scheme, a primary and a backup LSP are computed and setup at the provisioning time prior to failures.

This is because the bandwidth of the link is shared among the different LSPs and the reason why the previous explained protection scheme is not preferred.

When this occurs, a fault indication signal (FIS) is sent back to the head-end LSR that will immediately switch the traffic to the backup LSP.