Long Thin Networks
RFC 2757

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• 03

Network Working Group                                      G. Montenegro
Request for Comments: 2757                        Sun Microsystems, Inc.
Category: Informational                                       S. Dawkins
                                                         Nortel Networks
                                                                 M. Kojo
                                                  University of Helsinki
                                                               V. Magret
                                                                 Alcatel
                                                               N. Vaidya
                                                    Texas A&M University
                                                            January 2000

                           Long Thin Networks

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   In view of the unpredictable and problematic nature of long thin
   networks (for example, wireless WANs), arriving at an optimized
   transport is a daunting task.  We have reviewed the existing
   proposals along with future research items. Based on this overview,
   we also recommend mechanisms for implementation in long thin
   networks.

   Our goal is to identify a TCP that works for all users, including
   users of long thin networks. We started from the working
   recommendations of the IETF TCP Over Satellite Links (tcpsat) working
   group with this end in mind.

   We recognize that not every tcpsat recommendation will be required
   for long thin networks as well, and work toward a set of TCP
   recommendations that are 'benign' in environments that do not require
   them.

Montenegro, et al.           Informational                      [Page 1]
RFC 2757                   Long Thin Networks               January 2000

Table of Contents

   1 Introduction .................................................    3
      1.1 Network Architecture ....................................    5
      1.2 Assumptions about the Radio Link ........................    6
   2 Should it be IP or Not?  .....................................    7
      2.1 Underlying Network Error Characteristics ................    7
      2.2 Non-IP Alternatives .....................................    8
         2.2.1 WAP ................................................    8
         2.2.2 Deploying Non-IP Alternatives ......................    9
      2.3 IP-based Considerations .................................    9
         2.3.1 Choosing the MTU [Stevens94, RFC1144] ..............    9
         2.3.2 Path MTU Discovery [RFC1191] .......................   10
         2.3.3 Non-TCP Proposals ..................................   10
   3 The Case for TCP .............................................   11
   4 Candidate Optimizations ......................................   12
      4.1 TCP: Current Mechanisms .................................   12
         4.1.1 Slow Start and Congestion Avoidance ................   12
         4.1.2 Fast Retransmit and Fast Recovery ..................   12
      4.2 Connection Setup with T/TCP [RFC1397, RFC1644] ..........   14
      4.3 Slow Start Proposals ....................................   14
         4.3.1 Larger Initial Window ..............................   14
         4.3.2 Growing the Window during Slow Start ...............   15
            4.3.2.1 ACK Counting ..................................   15
            4.3.2.2 ACK-every-segment .............................   16
         4.3.3 Terminating Slow Start .............................   17
         4.3.4 Generating ACKs during Slow Start ..................   17
      4.4 ACK Spacing .............................................   17
      4.5 Delayed Duplicate Acknowlegements .......................   18
      4.6 Selective Acknowledgements [RFC2018] ....................   18
      4.7 Detecting Corruption Loss ...............................   19
         4.7.1 Without Explicit Notification ......................   19
         4.7.2 With Explicit Notifications ........................   20
      4.8 Active Queue Management .................................   21
      4.9 Scheduling Algorithms ...................................   21
      4.10 Split TCP and Performance-Enhancing Proxies (PEPs) .....   22
         4.10.1 Split TCP Approaches ..............................   23
         4.10.2 Application Level Proxies .........................   26
         4.10.3 Snoop and its Derivatives .........................   27
         4.10.4 PEPs to handle Periods of Disconnection ...........   29
      4.11 Header Compression Alternatives ........................   30
      4.12 Payload Compression ....................................   31