Improved Approximations for Relative Survivable Network Design

Michael Dinitz, Ama Koranteng, Guy Kortsarz, Zeev Nutov

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


One of the most important and well-studied settings for network design is edge-connectivity requirements. This encompasses uniform demands (e.g. the Minimum k-Edge-Connected Spanning Subgraph problem), as well as nonuniform demands (e.g. the Survivable Network Design problem (SND)). In a recent paper [Dinitz, Koranteng, Kortsarz APPROX ’22], the authors observed that a weakness of these formulations is that we cannot consider fault-tolerance in graphs that have small cuts but where some large fault sets can still be accommodated. To remedy this, they introduced new variants of these problems under the notion relative fault-tolerance. Informally, this requires not that two nodes are connected if there are a bounded number of faults (as in the classical setting), but that they are connected if there are a bounded number of faults and the nodes are connected in the underlying graph post-faults. Due to difficulties introduced by this new notion of fault-tolerance, the results in [Dinitz, Koranteng, Kortsarz APPROX ’22] are quite limited. For the Relative Survivable Network Design problem (RSND) with non-uniform demands, they are only able to give a nontrivial result when there is a single demand with connectivity requirement 3—a non-optimal 27/4-approximation. We strengthen this result in two significant ways: We give a 2-approximation for RSND when all requirements are at most 3, and a -approximation for RSND with a single demand of arbitrary value k. To achieve these results, we first use the “cactus representation” of minimum cuts to give a lossless reduction to normal SND. Second, we extend the techniques of [Dinitz, Koranteng, Kortsarz APPROX’22] to prove a generalized and more complex version of their structure theorem, which we then use to design a recursive approximation algorithm.

Original languageEnglish
Title of host publicationApproximation and Online Algorithms - 21st International Workshop, WAOA 2023, Proceedings
EditorsJarosław Byrka, Andreas Wiese
PublisherSpringer Science and Business Media Deutschland GmbH
Number of pages15
ISBN (Print)9783031498145
StatePublished - 2023
Event21st International Workshop on Approximation and Online Algorithms, WAOA 2023 - Amsterdam, Netherlands
Duration: 7 Sep 20238 Sep 2023

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume14297 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference21st International Workshop on Approximation and Online Algorithms, WAOA 2023

Bibliographical note

Publisher Copyright:
© 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.


  • Fault tolerance
  • Network design


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