We study a multi-call variant of the classic PUSH&PULL rumor spreading process where nodes can contact k of their neighbors instead of a single one during both PUSH and PULL operations. We show that rumor spreading can be made faster at the cost of an increased amount of communication between the nodes. As a motivating example, consider the process on a complete graph of n nodes: while the standard PUSH&PULL protocol takes Θ(log n) rounds, we prove that our k-PUSH&PULL variant completes in Θ(log_{k} n) rounds, with high probability. We generalize this result in an expansion-sensitive way, as has been done for the classic PUSH&PULL protocol for different notions of expansion, e.g., conductance and vertex expansion. We consider small-set vertex expanders, graphs in which every sufficiently small subset of nodes has a large neighborhood, ensuring strong local connectivity. In particular, when the expansion parameter satisfies ϕ > 1, these graphs have a diameter of o(log n), as opposed to other standard notions of expansion. Since the graph’s diameter is a lower bound on the number of rounds required for rumor spreading, this makes small-set expanders particularly well-suited for fast information dissemination. We prove that k-PUSH&PULL takes O(log_{ϕ} n ⋅ log_{k} n) rounds in these expanders, with high probability. We complement this with a simple lower bound of Ω(log_{ϕ} n+ log_{k} n) rounds.
@InProceedings{cruciani_et_al:LIPIcs.DISC.2025.26, author = {Cruciani, Emilio and Forster, Sebastian and de Vos, Tijn}, title = {{Towards Constant Time Multi-Call Rumor Spreading on Small-Set Expanders}}, booktitle = {39th International Symposium on Distributed Computing (DISC 2025)}, pages = {26:1--26:25}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-402-4}, ISSN = {1868-8969}, year = {2025}, volume = {356}, editor = {Kowalski, Dariusz R.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.26}, URN = {urn:nbn:de:0030-drops-248434}, doi = {10.4230/LIPIcs.DISC.2025.26}, annote = {Keywords: small set expansion, vertex expansion, rumor spreading, multi-call rumor spreading, push\&pull protocol} }