deploying and managing ip over wdm networks - Index of

64 Deploying and Managing IP over WDM Networks
whereas at the connection level, the protection occurs between the two end
points of the path. The following sections describe these in more detail.
4.4.2.1 Link Protection/Restoration
In this case the protection or back-up path is disjointed from the working path
at the particular link over which protection is required. When the protected link
fails, traffic on the working path is switched over to the protection path. This is
a local repair method that can be potentially fast. Figure 4.3 illustrates this principle;
a working fiber is used for transferring the information, while a counterpropagating
protection fiber is dedicated to protection purposes. Signals added
to the ring are split across both fibers, and the destination node will take the best
signal of both.
At the OCh layer, similarly to the SDH protection, we have the following
schemes (for ring topologies) [11]:
• The optical channel dedicated protection ring (OChDPRING) is a 1+1
protection mechanism that uses two physically separated media (e.g.,
different fibers that for instance transport traffic in the opposite direction
of the ring). In case of a two-fiber ring network, one fiber will carry
the working signal while the counteracting fiber will carry the protection
signal at the same wavelength. This means that the traffic entering
the ring will be copied and transported twice across the ring. The destination
node of the ring will select the best signal.
• The optical channel shared protection ring (OChSPRING) can be considered
a 1:1 subnetwork connection (SNC) protection mechanism. In
a two-fiber ring architecture, one fiber will carry on half of the available
OCh space working OCh signals, and the other half is used to protect
OADM
OADM OADM
OADM
Figure 4.3 Link protection in an optical ring.
Working channel
Protection channel