rfc1045.txt

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Network Working Group                                     David Cheriton
Request for Comments:  1045                          Stanford University
                                                           February 1988


              VMTP: VERSATILE MESSAGE TRANSACTION PROTOCOL
                         Protocol Specification



STATUS OF THIS MEMO

This RFC describes a protocol proposed as a standard for the Internet
community.  Comments are encouraged.  Distribution of this document is
unlimited.


OVERVIEW

This memo specifies the Versatile Message Transaction Protocol (VMTP)
[Version 0.7 of 19-Feb-88], a transport protocol specifically designed
to support the transaction model of communication, as exemplified by
remote procedure call (RPC).  The full function of VMTP, including
support for security, real-time, asynchronous message exchanges,
streaming, multicast and idempotency, provides a rich selection to the
VMTP user level.  Subsettability allows the VMTP module for particular
clients and servers to be specialized and simplified to the services
actually required.  Examples of such simple clients and servers include
PROM network bootload programs, network boot servers, data sensors and
simple controllers, to mention but a few examples.




RFC 1045                       VMTP                        February 1988 


                           Table of Contents

1. Introduction                                                        1

   1.1. Motivation                                                     2
       1.1.1. Poor RPC Performance                                     2
       1.1.2. Weak Naming                                              3
       1.1.3. Function Poor                                            3
   1.2. Relation to Other Protocols                                    4
   1.3. Document Overview                                              5

2. Protocol Overview                                                   6

   2.1. Entities, Processes and Principals                             7
   2.2. Entity Domains                                                 9
   2.3. Message Transactions                                          10
   2.4. Request and Response Messages                                 11
   2.5. Reliability                                                   12
       2.5.1. Transaction Identifiers                                 13
       2.5.2. Checksum                                                14
       2.5.3. Request and Response Acknowledgment                     14
       2.5.4. Retransmissions                                         15
       2.5.5. Timeouts                                                15
       2.5.6. Rate Control                                            18
   2.6. Security                                                      19
   2.7. Multicast                                                     21
   2.8. Real-time Communication                                       22
   2.9. Forwarded Message Transactions                                24
   2.10. VMTP Management                                              25
   2.11. Streamed Message Transactions                                25
   2.12. Fault-Tolerant Applications                                  28
   2.13. Packet Groups                                                29
   2.14. Runs of Packet Groups                                        31
   2.15. Byte Order                                                   32
   2.16. Minimal VMTP Implementation                                  33
   2.17. Message vs. Procedural Request Handling                      33
   2.18. Bibliography                                                 34

3. VMTP Packet Formats                                                37

   3.1. Entity Identifier Format                                      37
   3.2. Packet Fields                                                 38







Cheriton                                                        [page i]



RFC 1045                       VMTP                        February 1988 


   3.3. Request Packet                                                45
   3.4. Response Packet                                               47

4. Client Protocol Operation                                          49

   4.1. Client State Record Fields                                    49
   4.2. Client Protocol States                                        51
   4.3. State Transition Diagrams                                     51
   4.4. User Interface                                                52
   4.5. Event Processing                                              53
   4.6. Client User-invoked Events                                    54
       4.6.1. Send                                                    54
       4.6.2. GetResponse                                             56
   4.7. Packet Arrival                                                56
       4.7.1. Response                                                58
   4.8. Management Operations                                         61
       4.8.1. HandleNoCSR                                             62
   4.9. Timeouts                                                      64

5. Server Protocol Operation                                          66

   5.1. Remote Client State Record Fields                             66
   5.2. Remote Client Protocol States                                 66
   5.3. State Transition Diagrams                                     67
   5.4. User Interface                                                69
   5.5. Event Processing                                              70
   5.6. Server User-invoked Events                                    71
       5.6.1. Receive                                                 71
       5.6.2. Respond                                                 72
       5.6.3. Forward                                                 73
       5.6.4. Other Functions                                         74
   5.7. Request Packet Arrival                                        74
   5.8. Management Operations                                         78
       5.8.1. HandleRequestNoCSR                                      79
   5.9. Timeouts                                                      82

6. Concluding Remarks                                                 84

I. Standard VMTP Response Codes                                       85

II. VMTP RPC Presentation Protocol                                    87








Cheriton                                                       [page ii]



RFC 1045                       VMTP                        February 1988 


   II.1. Request Code Management                                      87

III. VMTP Management Procedures                                       89

   III.1. Entity Group Management                                    100
   III.2. VMTP Management Digital Signatures                         101

IV. VMTP Entity Identifier Domains                                   102

   IV.1. Domain 1                                                    102
   IV.2. Domain 3                                                    104
   IV.3. Other Domains                                               105
   IV.4. Decentralized Entity Identifier Allocation                  105

V. Authentication Domains                                            107

   V.1. Authentication Domain 1                                      107
   V.2. Other Authentication Domains                                 107

VI. IP Implementation                                                108

VII. Implementation Notes                                            109

   VII.1. Mapping Data Structures                                    109
   VII.2. Client Data Structures                                     111
   VII.3. Server Data Structures                                     111
   VII.4. Packet Group transmission                                  112
   VII.5. VMTP Management Module                                     113
   VII.6. Timeout Handling                                           114
   VII.7. Timeout Values                                             114
   VII.8. Packet Reception                                           115
   VII.9. Streaming                                                  116
   VII.10. Implementation Experience                                 117

VIII. UNIX 4.3 BSD Kernel Interface for VMTP                         118

Index                                                                120












Cheriton                                                      [page iii]



RFC 1045                       VMTP                        February 1988 


                            List of Figures

   Figure 1-1:   Relation to Other Protocols                           4
   Figure 3-1:   Request Packet Format                                45
   Figure 3-2:   Response Packet Format                               47
   Figure 4-1:   Client State Transitions                             52
   Figure 5-1:   Remote Client State Transitions                      68
   Figure III-1:   Authenticator Format                               92
   Figure VII-1:   Mapping Client Identifier to CSR                  109
   Figure VII-2:   Mapping Server Identifiers                        110
   Figure VII-3:   Mapping Group Identifiers                         111






































Cheriton                                                       [page iv]

RFC 1045                       VMTP                        February 1988 


1. Introduction

The Versatile Message Transaction Protocol (VMTP) is a transport
protocol designed to support remote procedure call (RPC) and general
transaction-oriented communication.  By transaction-oriented
communication, we mean that:

   - Communication is request-response:  A client sends a request
     for a service to a server, the request is processed, and the
     server responds.  For example, a client may ask for the next
     page of a file as the service.  The transaction is terminated
     by the server responding with the next page.

   - A transaction is initiated as part of sending a request to a
     server and terminated by the server responding.  There are no
     separate operations for setting up or terminating associations
     between clients and servers at the transport level.

   - The server is free to discard communication state about a
     client between transactions without causing incorrect behavior
     or failures.

The term message transaction (or transaction) is used in the reminder of
this document for a request-response exchange in the sense described
above.

VMTP handles the error detection, retransmission, duplicate suppression
and, optionally, security required for transport-level end-to-end
reliability.

The protocol is designed to provide a range of behaviors within the
transaction model, including:

   - Minimal two packet exchanges for short, simple transactions.

   - Streaming of multi-packet requests and responses for efficient
     data transfer.