RFC 1151 (rfc1151) - Page 1 of 4

Version 2 of the Reliable Data Protocol (RDP)

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Network Working Group                                      C. Partridge
Request for Comments: 1151                 BBN Systems and Technologies
Updates: RFC 908                                              R. Hinden
                                               BBN Communications Corp.
                                                             April 1990


             Version 2 of the Reliable Data Protocol (RDP)

Status of this Memo

   This RFC suggests several updates to the specification of the
   Reliable Data Protocol (RDP) in RFC-908 based on experience with the
   protocol.  This revised version of the protocol is experimental.

   Distribution of this memo is unlimited.

Introduction

   Experiments in 1986 and 1987 turned up some ambiguities and problems
   with the RDP specification.  At the time, it was hoped that the
   authors might find the time to revise the entire RDP specification to
   fix these problems, however given the limited demand for RDP
   implementations, the authors were never able to justify the time
   involved in revising the spec.  This document lists the changes that
   we believe are appropriate to make to RDP version 1.

   Readers are expected to be familiar with RFC-908.

Changes To The Protocol Header

   There are three changes to the protocol header: the checksum
   algorithm has been changed, the port size increased, and the version
   number incremented.  The new header format is shown in Figure 1.

   The major discovery during the testing of the protocol is that cost
   of computing the the RDP checksum proved surprisingly variable; its
   performance was more heavily affected by the host's data
   representation than anticipated.  Optimized checksum implementations
   on two comparable hardware bases gave performance that differed by a
   factor of five.  Since the speed of the checksum is a key factor in
   the performance of the protocol itself, this variation caused a
   noticeable difference in throughput.

   The wide variation in performance on comparable machines was felt to
   be undesirable, so the checksum has been changed.  RDP now uses the
   16-bit TCP checksum, which is specified on page 16 of RFC-793.




Partridge & Hinden
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