In the world we live in, the seamless operation of the computer and information networks is essential
question. The optical networks provide high speed data which is really tempting for the Service
Providers, more and more of them decide to change their core networks to be optical. The benefits of the
optical networks are great, but it requires a considered network planning to avoid failures. The most and
well-known methods work with slow and complicated signalling, which makes the failure restoration
time to overgrow the time given by the upper layer’s protocols.
The monitoring trails are the solution combined with failure dependent protection to reach single
link failure protection for the whole network without sending signals. For the Service Providers it is
not enough, in the real networks the multi link failures are common. This makes an interesting research
field how to localize multi link failures and how to protect network from them. In my thesis I give a
proposal to how to localize independent double link failures. With this method we can localize any
single link failure after the first failure is localized. I designed this method to be compatible with the
existing technology used with monitoring trails. I made the solution to be an extension of the single link
localizing method. This extension can be separated and the solution uses a little more extra capacity than
the single link failure solution.
With simulations and a case study I investigated the solution, which proved to be better than the
existing solution for NL-UFL (Network-wide local Unambiguous Failure Localization). The proposal
can be developed in the future to be useful with simultaneous double link failure localization, which also
is an interesting research field.