Information Technology Reference
In-Depth Information
2.2.1. Path-Based Dedicated Protection [13]
In this scheme, one dedicated protection path, which is link-disjoint from the working
path, is reserved for each working path in advance. Since a protection resource is dedicated
for each protection path, the configuration of equipments along the path can be performed in
advance. This pre-configuration process can reduce restoration time. When a failure takes
place, the source node can switch the traffic to the protection path without consuming extra
time waiting for signaling and configuration processes. Advantage of this scheme is its simple
design; however, its disadvantage is that it eliminates sharing benefits, which results in a large
capacity needed for protection. The 1+1 Protection
This is a kind of Path-based dedicated protection scheme in which there are two links or
nodes with separated path for ensuring of sending information connectivity service in case of
having defect in network elements. The signal is sent over both working and backup paths at
the same time. Under a failure situation, a receiving terminal chooses the best signal
according to local information about the signal quality. Line efficiency is supported with
allocating protection channel for each working channel [1]. Figure 5 illustrates a
configuration example for two demands, F-N and F-H. Both demands are routed along two
node-disjoint paths. It is obvious that the required minimum capacity is twice the amount of
network capacity needed to transport the traffic demand as in the unprotected case [11].
Figure 5. Example of 1+1 protection.
2.2.2. Path-Based Shared Protection
The essence of this protection scheme is the sharing of protection resources among
working paths. However, a protection path cannot be shared among links that may fail
simultaneously. In other words, if working paths are separate, it is possible to share backup
resources. Usually, the purpose of this scheme is to choose the protection path where the
amount of the reserved capacity for protection is minimized. Since equipments like optical
switches are shared amongst several working paths, the equipment configuration for
protection is commonly performed after a failure takes place. End nodes of a failed link can
detect the failure and send the signaling message to each network node in protection path to
adjust process. Then, the source node can switch its current traffic on the protection path. In
shared path protection, the backup paths are predefined and capacity (wavelength) is reserved,
Search WWH ::

Custom Search