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Survivability of Optical Networks
Published in Partha Pratim Sahu, Advances in Optical Networks and Components, 2020
In path protection [2], the traffic is transmitted through a backup path (or protection path) after a link failure occurs on its working/primary path. The primary and backup paths for a connection must have different link so that no single-link failure can affect both of these paths. In link protection, the traffic is transmitted only around the failed link. The path protection gives more utilization of backup resources and has lower end-to-end propagation delay for the recovered route, whereas link protection gives faster protection-switching time. UPSR uses path protection in a ring, whereas BLSR follows link protection implemented in a ring. Figure 7.5 shows the operation of link protection and path protection. The path protection schemes are made in two ways: dedicated (1 + 1 and 1:1) and shared (M:N), whereas link protection scheme is also made by dedicated-link and shared-link protection.
Reliability in MPLS-Based Metropolitan Area Networks
Published in Nam-Kee Tan, MPLS for Metropolitan Area Networks, 2004
In the event that a link or node failure occurs along a primary LSP without its corresponding secondary LSP being defined, the ingress LSR will continue to forward traffic toward its destination as native IP packets using the IGP shortest path if such a path is available. The types of protection implemented by MPLS-TE against LSP outages include: Link protection: The purpose of LSP link protection is to protect an LSP from a specific link failure. Under link protection, the path of the backup LSP (or the secondary LSP) is disjoint from the path of the primary LSP at the particular link over which protection is required. When the protected link fails, traffic on the primary LSP is switched over to the backup LSP at the head end of the failed link. This is commonly referred to as local repair (or local protection), whereby protection is against a single link or node failure.Node protection: The purpose of LSP node protection is to protect an LSP from a specific node failure. Under node protection/restoration, the path of the backup LSP is disjoint from the path of the primary LSP at the particular node to be protected. When the node fails, traffic on the primary LSP is switched over to the backup LSP at the upstream LSR that is directly connected to the failed node. Node protection is also part of the local repair scheme.Path protection: Path protection is intended to protect an LSP from failure at any point along its routed path. Under path protection, the path of the backup LSP is completely disjoint from the path of the primary LSP (with no fate sharing). The advantage of path protection is that the backup LSP protects the primary LSP from all possible link and node failures along the path, except for failures that occur at the ingress and egress LSRs, or for correlated failures that can impact both primary and backup paths at the same time. In other words, path protection is a global repair (or global protection) technique in which the protection is against any link or node failure along the LSP. Because the path selection is end to end based, path protection is more efficient from the resource usage perspective than link or node protection. Nevertheless, because restoration is localized, the failover time of link or node protection is considerably faster than path protection, in which remote nodes must be notified of failures.
An offline scheme for reducing cost of protection in all-optical WDM mesh networks with fast recovery
Published in International Journal of Parallel, Emergent and Distributed Systems, 2019
Vishal Dey, Abhishek Bandyopadhyay, Uma Bhattacharya, Monish Chatterjee
In contrast to link protection schemes, path protection schemes provide protection for an entire primary path. In path protection schemes for every primary (or working) path, a backup path link-disjoint with the primary is pre-computed and resources are allocated in advance so that the traffic on the primary path can be switched on to the backup path in the event of a link failure on the primary path. But some delay is introduced to make the backup path operational due to signaling that is required between the routers on the path before any communication can be initiated. This setup delay can be avoided in all-optical networks if the photonic cross-connects (PXCs) at every node on the backup path are preconfigured to forward the traffic to its successor node at a given wavelength before the occurrence of a fault [4].