These are discussed next.
Restoration
A key consideration in carrier networks is protection and restoration. Rapid restoration
on an Ethernet switches could be done using an additional layer, MPLS. This adds complexity
and increases OpEx for any carrier adopting MPLS for protection in the metro
network. The approach requires manual configuration of the MPLS protection paths.
These functions are automated at Layer 2 in the RPR protocol. Sub 50 ms restoration
and the substantial elimination of jitter, delay, and packet loss are the result of the
signaling protocol that is native to the RPR MAC.
The standard defines two protection mechanisms: Steer (mandatory), and Wrap (optional).
It is important to have both mechanisms available since they have different
uses. They are designed to overcome fundamental issues that arise during a protection
event. Packets are either mis-ordered, lost, or delayed. Each of these events has an
impact on services. Table 12.3 shows how steering or wrapping affect applications.
In addition, unlike SONET/SDH restoration mechanisms, RPR restoration mechanisms
have the ability to partially restore a service.
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