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Fast-Slow Retransmission Timeout and Congestion Control Algorithm for CoAP

Document Type Expired Internet-Draft (core WG)
Expired & archived
Authors Ilpo Järvinen , Markku Kojo , Iivo Raitahila , Zhen Cao
Last updated 2023-09-14 (Latest revision 2023-03-13)
Replaces draft-jarvinen-core-fasor
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
Additional resources Working Group Repo
Mailing list discussion
Stream WG state WG Document
Document shepherd (None)
IESG IESG state Expired
Consensus boilerplate Unknown
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft is available in these formats:


This document specifies an alternative retransmission timeout (RTO) and congestion control back off algorithm for the CoAP protocol, called Fast-Slow RTO (FASOR). The algorithm specified in this document employs an appropriate and large enough back off of RTO as the major congestion control mechanism to allow acquiring unambiguous RTT samples with high probability and to prevent building a persistent queue when retransmitting. The algorithm also aims to retransmit quickly using an accurately managed RTO when link-errors are occuring, basing RTO calculation on unambiguous round-trip time (RTT) samples.


Ilpo Järvinen
Markku Kojo
Iivo Raitahila
Zhen Cao

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)