TCP Usage Guidance in the Internet of Things (IoT)
draft-ietf-lwig-tcp-constrained-node-networks-13

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LWIG Working Group                                              C. Gomez
Internet-Draft                                                       UPC
Intended status: Informational                              J. Crowcroft
Expires: May 3, 2021                             University of Cambridge
                                                               M. Scharf
                                                    Hochschule Esslingen
                                                        October 30, 2020

           TCP Usage Guidance in the Internet of Things (IoT)
            draft-ietf-lwig-tcp-constrained-node-networks-13

Abstract

   This document provides guidance on how to implement and use the
   Transmission Control Protocol (TCP) in Constrained-Node Networks
   (CNNs), which are a characteristic of the Internet of Things (IoT).
   Such environments require a lightweight TCP implementation and may
   not make use of optional functionality.  This document explains a
   number of known and deployed techniques to simplify a TCP stack as
   well as corresponding tradeoffs.  The objective is to help embedded
   developers with decisions on which TCP features to use.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 3, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of

Gomez, et al.              Expires May 3, 2021                  [Page 1]
Internet-Draft                 TCP in IoT                   October 2020

   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Characteristics of CNNs relevant for TCP  . . . . . . . . . .   4
     2.1.  Network and link properties . . . . . . . . . . . . . . .   4
     2.2.  Usage scenarios . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Communication and traffic patterns  . . . . . . . . . . .   6
   3.  TCP implementation and configuration in CNNs  . . . . . . . .   6
     3.1.  Addressing path properties  . . . . . . . . . . . . . . .   7
       3.1.1.  Maximum Segment Size (MSS)  . . . . . . . . . . . . .   7
       3.1.2.  Explicit Congestion Notification (ECN)  . . . . . . .   8
       3.1.3.  Explicit loss notifications . . . . . . . . . . . . .   9
     3.2.  TCP guidance for single-MSS stacks  . . . . . . . . . . .   9
       3.2.1.  Single-MSS stacks - benefits and issues . . . . . . .   9
       3.2.2.  TCP options for single-MSS stacks . . . . . . . . . .  10
       3.2.3.  Delayed Acknowledgments for single-MSS stacks . . . .  10
       3.2.4.  RTO calculation for single-MSS stacks . . . . . . . .  11
     3.3.  General recommendations for TCP in CNNs . . . . . . . . .  12
       3.3.1.  Loss recovery and congestion/flow control . . . . . .  12
         3.3.1.1.  Selective Acknowledgments (SACK)  . . . . . . . .  13
       3.3.2.  Delayed Acknowledgments . . . . . . . . . . . . . . .  13
       3.3.3.  Initial Window  . . . . . . . . . . . . . . . . . . .  14
   4.  TCP usage recommendations in CNNs . . . . . . . . . . . . . .  14
     4.1.  TCP connection initiation . . . . . . . . . . . . . . . .  14
     4.2.  Number of concurrent connections  . . . . . . . . . . . .  15
     4.3.  TCP connection lifetime . . . . . . . . . . . . . . . . .  15
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   7.  Annex. TCP implementations for constrained devices  . . . . .  18
     7.1.  uIP . . . . . . . . . . . . . . . . . . . . . . . . . . .  19
     7.2.  lwIP  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
     7.3.  RIOT  . . . . . . . . . . . . . . . . . . . . . . . . . .  19
     7.4.  TinyOS  . . . . . . . . . . . . . . . . . . . . . . . . .  20