page_title: P-cycle protection
section_title: Overview of the p-Cycle
hierarchical_section_title: P-cycle protection / Overview of the p-Cycle
caption_attribution_description: English: Hamiltonian p-cycle
context_page_description: The p-Cycle protection scheme is a technique to protect a mesh network from a failure of a link, with the benefits of ring like recovery speed and mesh-like capacity efficiency, similar to that of a shared backup path protection. p-Cycle protection was invented in late 1990s, with research and development done mostly by Wayne D. Grover, and D. Stamatelakis.
context_section_description: In Transport communication networks two methods were developed and introduced for restoration and recovery, one was a ring-based protection and the other was mesh restoration. The ring based protection offered a quick recovery time at the expense of higher capacity redundancy, while the mesh restoration offered better capacity-efficiency at the expense of slower recovery times. In 1998 the p-Cycle became a promising technique for recovery in mesh networks because of the combined benefits of ring network recovery speed and mesh like capacity efficiency. In a mesh network, the spare capacity is used to create the ring like structures as shown in Figure 1. Due to the nature of the rings assuming bi-directional line switched ring (BLSR), only 2 end nodes are involved in a case of a link failure to switch traffic to a pre-planned cycle (path) and recover, as it is demonstrated in Figure 2.
  One of the key differences between a ring-based scheme and the p-cycle scheme is the ability of the p-cycle to protect links that are not on the p-cycle ring as shown in Figure 3. The ability to protect two channel for every spare channel that is assigned to the p-cycle allows to achieve mesh-like capacity efficiency. This feature gives the p-cycle the additional efficiency over the ring-based schemes. "Another over looked feature of the p-Cycle is that working paths may be freely routed over the network graph and are not limited to follow the ring-constrained routings".
caption: Fig 4. A Hamiltonian p-cycle, the protection path passes through all the nodes in the network only once
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