Survivability

Survivability is the capability of a system to fulfil its mission in a timely manner in the presence of attacks, failures, or accidents. The mission of a system is defined to be a set of very high-level requirements or goals. The notion of survivability itself draws upon other properties including security, fault tolerance and reliability, thus making it heavily dependent on how these other properties are tackled within the architecture.

To maintain their ability to deliver their services, for a system to be survivable it must exhibit four properties:

• Resistance to attacks. The system must possess strategies for repelling attacks. This draws upon the security property.
• Recognition of attacks and the extent of damage. The system must possess strategies for detecting attacks and to evaluate the extent of any damage. This draws upon security and fault tolerance properties.
• Recovery of full and essential services after an attack. The system must possess strategies for restoring compromised information or functionality, whilst limiting the extent of the damage. This draws upon the fault tolerance and repairability properties.
• Adaptation and evolution to reduce effectiveness of future attacks. The system must possess strategies for improving survivability based on experienced gained from attacks.

Survivability in P2P systems raises some interesting issues, as in some cases the inherent redundancy can help attain survivability, whilst the lack of a central control can hinder it. The choice of architecture can affect how easy it is to achieve these four properties.