deploying and managing ip over wdm networks - Index of

60 Deploying and Managing IP over WDM Networks
• Optical transmission section supervisory functions for enabling
section-level operations and management functions, such as transmission
section survivability.
As the OTS layer is the lowest layer of the OTN, all of its network connections
are supported directly by the optical media layer. Because this optical layer
does not contain active components, server failure errors will not be received,
unlike the other OTN layers.
4.3.2 Optical Transport Services
Because the traffic-carrying wavelengths in a WDM-based OTN provide great
bit-rate and protocol independence, such an OTN can be seen as a server layer
that can carry different client signals (IP, ATM, and SDH). From this point of
view, the OTN provides transport services to the upper layers. Three categories
of transport services can be identified:
1. Leased OCh service. An OCh can be set up either using the network
management resulting in a permanent set up or using signaling and
routing protocols, which is more flexible.
2. Leased wavelength. The customer of this service should be equipped
with colored line terminals.
3. Leased dark fiber. In this case, the provider of this service has no control
of the fiber, and the customer can use it according to his or her
needs.
From a carrier’s point of view, the provision of lightpaths to the customers
can be classified into the following categories:
• Lightpaths that must be protected in the optical layer. In this category, the
client layer relies on the optical layer for protection and has no restoration/protection
mechanism itself.
• Lightpaths that must not be protected in the optical layer. An example in
this category is SONET/SDH signals that rely on the protection/restoration
mechanism of the SONET/SDH layer.
• Lightpaths that are indifferent to protection. IP traffic fits in this category,
because IP has its own mechanism for protection by rerouting the traffic
around the affected segment of the network. However, protection at
the optical layer is welcome because it takes less time to protect in the
optical layer than it does rerouting in the IP.