RFC 1151 (rfc1151) - Page 1 of 4
Version 2 of the Reliable Data Protocol (RDP)
Alternative Format: Original Text Document
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