We present several new proofs of lower bounds for the space-stretch tradeoff in labeled network routing. First, we give a new proof of an important result of Cyril Gavoille and Marc Gengler that any routing scheme with stretch < 3 must use Ω(n) bits of space at some node on some network with n vertices, even if port numbers can be changed. Compared to the original proof, our proof is significantly shorter and, we believe, conceptually and technically simpler. A small extension of the proof can show that, in fact, any constant fraction of the n nodes must use Ω(n) bits of space on some graph. Our main contribution is a new result that if port numbers are chosen adversarially, then stretch < 2k+1 implies some node must use Ω(n^(1/k) log n) bits of space on some graph, assuming a girth conjecture by Erdős. We conclude by showing that all known methods of proving a space lower bound in the labeled setting, in fact, require the girth conjecture.
@InProceedings{zinovyev:LIPIcs.DISC.2022.37, author = {Zinovyev, Anatoliy}, title = {{Space-Stretch Tradeoff in Routing Revisited}}, booktitle = {36th International Symposium on Distributed Computing (DISC 2022)}, pages = {37:1--37:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-255-6}, ISSN = {1868-8969}, year = {2022}, volume = {246}, editor = {Scheideler, Christian}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.37}, URN = {urn:nbn:de:0030-drops-172281}, doi = {10.4230/LIPIcs.DISC.2022.37}, annote = {Keywords: Compact routing, labeled network routing, lower bounds} }
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