RFC 908 (rfc908) - Page 1 of 57
Reliable Data Protocol
Alternative Format: Original Text Document
Reliable Data Protocol
RFC-908
David Velten
Robert Hinden
Jack Sax
BBN Communications Corporation
July 1984
Status of This Memo
This RFC specifies a proposed protocol for the ARPA Internet
community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
RDP Specification
Table of Contents
1 Introduction.......................................... 1
2 General Description................................... 3
2.1 Motivation.......................................... 3
2.2 Relation to Other Protocols......................... 5
3 Protocol Operation.................................... 7
3.1 Protocol Service Objectives......................... 7
3.2 RDP Connection Management........................... 7
3.2.1 Opening a Connection.............................. 8
3.2.2 Ports............................................. 8
3.2.3 Connection States................................. 8
3.2.4 Connection Record................................ 11
3.2.5 Closing a Connection............................. 13
3.2.6 Detecting an Half-Open Connection................ 14
3.3 Data Communication................................. 14
3.4 Reliable Communication............................. 15
3.4.1 Segment Sequence Numbers......................... 15
3.4.2 Checksums........................................ 16
3.4.3 Positive Acknowledgement of Segments............. 16
3.4.4 Retransmission Timeout........................... 17
3.5 Flow Control and Window Management................. 17
3.6 User Interface..................................... 19
3.7 Event Processing................................... 20
3.7.1 User Request Events.............................. 21
3.7.2 Segment Arrival Events........................... 24
3.7.3 Timeout Events................................... 29
4 RDP Segments and Formats............................. 31
4.1 IP Header Format................................... 31
4.2 RDP Header Format.................................. 32
4.2.1 RDP Header Fields................................ 33
4.3 SYN Segment........................................ 36
4.3.1 SYN Segment Format............................... 36
4.3.2 SYN Segment Fields............................... 37
4.4 ACK Segment........................................ 38
4.4.1 ACK Segment Format............................... 38
4.4.2 ACK Segment Fields............................... 39
4.5 Extended ACK Segment............................... 40
4.5.1 EACK Segment Format.............................. 40
4.5.2 EACK Segment Fields.............................. 40
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RFC-908 July 1984
4.6 RST Segment........................................ 42
4.6.1 RST Segment Format............................... 42
4.7 NUL Segment........................................ 43
4.7.1 NUL segment format............................... 43
5 Examples of Operation................................ 45
5.1 Connection Establishment........................... 45
5.2 Simultaneous Connection Establishment.............. 46
5.3 Lost Segments...................................... 47
5.4 Segments Received Out of Order..................... 48
5.5 Communication Over Long Delay Path................. 49
5.6 Communication Over Long Delay Path With Lost
Segments
.................................................... 50
5.7 Detecting a Half-Open Connection on Crash
Recovery
.................................................... 51
5.8 Detecting a Half-Open Connection from the
Active Side
.................................................... 52
A Implementing a Minimal RDP........................... 53
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RDP Specification
FIGURES
1 Relation to Other Protocols............................ 5
2 Form of Data Exchange Between Layers................... 6
3 RDP Connection State Diagram.......................... 10
4 Segment Format........................................ 31
5 RDP Header Format..................................... 32
6 SYN Segment Format.................................... 37
7 ACK Segment Format.................................... 38
8 EACK Segment Format................................... 41
9 RST Segment Format.................................... 42
10 NUL Segment Format................................... 43
Page iii
CHAPTER 1
Introduction
The Reliable Data Protocol (RDP) is designed to provide a
reliable data transport service for packet-based applications
such as remote loading and debugging. The protocol is intended
to be simple to implement but still be efficient in environments
where there may be long transmission delays and loss or non-
sequential delivery of message segments.
Although this protocol was designed with applications such
as remote loading and debugging in mind, it may be suitable for
other applications that require reliable message services, such
as computer mail, file transfer, transaction processing, etc.
Some of the concepts used come from a variety of sources.
The authors wish credit to be given to Eric Rosen, Rob Gurwitz,
Jack Haverty, and to acknowledge material adapted from "RFC-793,
The Transmission Control Protocol", edited by Jon Postel. Thanks
to John Linn for the checksum algorithm.
