Using virtual links for reliable information retrieval across point-to-point networks

The problem of establishing reliable communication across point-to-point networks is addressed. Several protocols are given, using node-disjoint paths to implement a set of independent virtual links (u-links) between each node pair. The u-links can be used to establish communication between the node pair provided the number and type of failures in the network are limited. Failed devices are classified by whether they are benign (delay and omission faults) or are malicious (not benign). The use of u-links is demonstrated with a protocol for remote information retrieval. With b benign and m malicious faults, retrieval can always be achieved if the graph connectivity exceeds b+2 m. This bound is tight. The authors give a flexible retrieval protocol; it analyzes the responses received thus far, and computes a minimum and maximum number of u-links to send (additional) retrieval requests. Maximal requests guarantee completion of the protocol upon their timeout. With minimal requests, protocol completion is barely possible with no further requests. u-links are extended so that they bounce requests when there is no response, which strengthens the retrieval protocol.