RFC 3819 (rfc3819) - Page 2 of 60

Advice for Internet Subnetwork Designers

RFC 3819        Advice for Internet Subnetwork Designers       July 2004


Table of Contents

   1.  Introduction and Overview. . . . . . . . . . . . . . . . . . .  2
   2.  Maximum Transmission Units (MTUs) and IP Fragmentation . . . .  4
       2.1.  Choosing the MTU in Slow Networks. . . . . . . . . . . .  6
   3.  Framing on Connection-Oriented Subnetworks . . . . . . . . . .  7
   4.  Connection-Oriented Subnetworks. . . . . . . . . . . . . . . .  9
   5.  Broadcasting and Discovery . . . . . . . . . . . . . . . . . . 10
   6.  Multicasting . . . . . . . . . . . . . . . . . . . . . . . . . 11
   7.  Bandwidth on Demand (BoD) Subnets. . . . . . . . . . . . . . . 13
   8.  Reliability and Error Control. . . . . . . . . . . . . . . . . 14
       8.1.  TCP vs Link-Layer Retransmission . . . . . . . . . . . . 14
       8.2.  Recovery from Subnetwork Outages . . . . . . . . . . . . 17
       8.3.  CRCs, Checksums and Error Detection. . . . . . . . . . . 18
       8.4.  How TCP Works. . . . . . . . . . . . . . . . . . . . . . 20
       8.5.  TCP Performance Characteristics. . . . . . . . . . . . . 22
             8.5.1.  The Formulae . . . . . . . . . . . . . . . . . . 22
             8.5.2.  Assumptions. . . . . . . . . . . . . . . . . . . 23
             8.5.3.  Analysis of Link-Layer Effects on TCP
                     Performance. . . . . . . . . . . . . . . . . . . 24
   9.  Quality-of-Service (QoS) Considerations. . . . . . . . . . . . 26
   10. Fairness vs Performance. . . . . . . . . . . . . . . . . . . . 29
   11. Delay Characteristics. . . . . . . . . . . . . . . . . . . . . 30
   12. Bandwidth Asymmetries. . . . . . . . . . . . . . . . . . . . . 31
   13. Buffering, Flow and Congestion Control . . . . . . . . . . . . 31
   14. Compression. . . . . . . . . . . . . . . . . . . . . . . . . . 34
   15. Packet Reordering. . . . . . . . . . . . . . . . . . . . . . . 36
   16. Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
   17. Routing. . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
   18. Security Considerations. . . . . . . . . . . . . . . . . . . . 41
   19. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 44
   20. Informative References . . . . . . . . . . . . . . . . . . . . 45
   21. Contributors' Addresses. . . . . . . . . . . . . . . . . . . . 57
   22. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 58
   23. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 60

1.  Introduction and Overview

   IP, the Internet Protocol [RFC 791] [RFC 2460], is the core protocol of
   the Internet.  IP defines a simple "connectionless" packet-switched
   network.  The success of the Internet is largely attributed to IP's
   simplicity, the "end-to-end principle" [SRC81] on which the Internet
   is based, and the resulting ease of carrying IP on a wide variety of
   subnetworks, not necessarily designed with IP in mind.  A subnetwork
   refers to any network operating immediately below the IP layer to
   connect two or more systems using IP (i.e., end hosts or routers).
   In its simplest form, this may be a direct connection between the IP
   systems (e.g., using a length of cable or a wireless medium).



Karn, et al.             Best Current Practice