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Fast-Slow Retransmission Timeout and Congestion Control Algorithm for CoAP

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft whose latest revision state is "Expired".
Expired & archived
Authors Ilpo Järvinen , Markku Kojo , Iivo Raitahila , Zhen Cao
Last updated 2021-04-22 (Latest revision 2020-10-19)
Replaces draft-jarvinen-core-fasor
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state WG Document
Document shepherd (None)
IESG IESG state Expired
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD (None)
Send notices to (None)

This Internet-Draft is no longer active.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 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 Retransmission Timeout (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 retransmission timeout 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.)