survivable network systems: its achievements and future directions

society is growing increasingly dependent upon large-scale, highly distributed systems that operate in unbounded open network environments. unless safeguards are incorporated in the system, a failure of even a single component, e.g. a link or a node, can significantly impact the network performance and can cause highly expensive damages. the discipline of survivability attempts to ensure that network systems can deliver essential services and maintains inherent properties such as integrity, confidentiality, and performance, in the presence of attacks, failures or accidents. optical networks based on wavelength-division multiplexing (wdm) technology can potentially transfer hundreds of gigabits of data per second in the network. wdm networks are believed to be a promising candidate to meet the explosive increase of bandwidth demand in the internet. however, the high capacity of a link has the drawback that a failure can potentially lead to the loss of a large amount of data. this is why the survivability performance of networks is an important research issue. the objective of this paper is to answer questions like “what does survivability mean?”, “why is it important?”, “how does it differ from fault tolerance?” and “how is it being measured?” by surveying the concepts of information and network survivability, its relation to and its distinction from dependability, fault tolerance and security. the survivability of optical networks and protection techniques in wdm networks are reviewed as an example of techniques to improve the network survivability. the problem of survivability measures from network analysis and design point of view is also presented in the paper.