1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefro
2、m, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.Copyright 2001 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.S.
3、A.TO PLACE A DOCUMENT ORDER: (724) 776-4970 FAX: (724) 776-0790 SAE WEB ADDRESS: http:/www.sae.org400 Commonwealth Drive, Warrendale, PA 15096-0001AEROSPACE INFORMATION REPORTAIR4886Issued 1996-04Reaffirmed 2001-10Statement on Requirements for Real-Time Communication Protocols (RTCP)FOREWORDThis doc
4、ument contains the requirements for the SAE AS-2A-1 Real-Time Communications Protocols (RTCP) as developed by the RTMT Group. These requirements are an edited compilation of those voiced by numerous military and commercial organizations primarily concerning aircraft applications. However, it is the
5、opinion of the Task Group that these requirements have general applicability to any distributed real-time control systems.A wide spectrum of industry representation has been tasked to define the requirements for a multinational, multiservice, commercially accepted military standard for real-time com
6、munication protocols. This effort was sponsored by SAE Interconnect Networks Committee AS-2. Inputs to this document have been consolidated from participating resources of the Department of Defenses military services, aerospace prime contractors, United Kingdom, France, Germany, electronic and LSI c
7、omponent suppliers, ARINC, commercial aviation equipment manufacturers and consumers, and systems consultants. The requirements defined herein discuss technical aspects based upon the following considerations:a. Functionsb. Performancec. Test Requirementsd. Operational Propertiese. Validation Requir
8、ementsCopyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-SAE AIR4886 - 2 -FOREWORD (Continued)Contacts:This document has been prepared by the Real-Time Model Task Group (RTMT) of the SAE AS-2A System, App
9、lication and Requirements Subcommittee, which is part of the AS-2 Interconnect Networks Committee of the SAE Avionics Systems Division. Correspondence concerning this document may be addressed to:Alan Birch, Chairman AS-2A-1 RTMT Group,GEC-Marconi Avionics Limited,ISG, Airport Works,Rochester, Kent,
10、 UK. ME1 2XX (44) 1634-844400 Ext 4731e-mail: Doug Johnson, Chairman AS-2A Subcommittee,CECOM C2SID,Department of Army,AMSEL-RD-C2-TS-I,Fort Monmouth, NJ 07703-5603 (1) 908 427-3284email: johnsod1doim6.monmouth.army.milNotice:Committee approval of the previous version of this document, identified as
11、 ARD50007, was obtained by mail ballot completed September 20, 1991. This AIR4886 was approved by the AS-2 Committee by mail ballot, October 26, 1995.Charter:The RTMT was chartered by the Systems, Applications, and Requirements Subcommittee (AS-2A) as followsThe Real-Time Model Task Group (RTMT) sha
12、ll define requirements for communication protocols specifically intended for real-time applications. These requirements are intended to complement SAE AS-2 communication standards and address the logical interface between the User and communication tasks and the functions allocated to communication
13、tasks.Systems for real-time applications are characterized by the presence of hard deadlines where failure to meet a deadline must be considered a system fault.In order to fulfill its commitment, RTMT will develop and maintain supporting documentation such as protocol assessment reports, requirement
14、s definition and logical interface specifications.RTMT supports and interacts with developers and users of lower level real-time protocols. RTMT sees as its mission to increase the understanding of the specificity of real-time communication needs. RTMT operates in liaison with ISO, NATO, IEEE, POSIX
15、, JIAWG, NGCR and other standardization groups worldwide.Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-SAE AIR4886 - 3 -TABLE OF CONTENTS1. SCOPE .52. REFERENCES .52.1 SAE Publications.52.2 U.S. Gove
16、rnment Publications53. INTRODUCTION 63.1 Target Applications Descriptions.63.1.1 Distributed.73.1.2 Interrupted Operational Performance83.1.3 Real-Time83.1.4 Highly Automated83.1.5 Control.83.1.6 Predefined System Configurations83.2 System Definition 84. REQUIREMENTS.94.1 General .94.1.1 Transfer To
17、pologies.94.1.1.1 Point-To-Point94.1.1.2 Broadcast124.1.1.3 Multicast124.1.1.4 Concentration124.1.1.5 Multiple Concentration 124.1.2 Semantic Importance 134.1.3 Performance Requirements 144.1.4 Automatic Function Allocation.144.1.5 RTCP Layers.154.1.6 RTCP Implementation.154.2 System Services .154.2
18、.1 Data Communication Services154.2.1.1 Category 1 Transfers 164.2.1.2 Category 2 Transfers 184.2.1.3 Message Size184.2.1.4 Packet Size .194.2.1.5 Flow Control194.2.1.6 Flow Restriction.214.2.1.7 Acknowledged and Nonacknowledged Services 224.2.2 Synchronization Service234.2.2.1 Remote Interrupts .23
19、4.2.2.2 Time Distribution .244.2.2.3 Related Data Streams.24Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-SAE AIR4886 - 4 -TABLE OF CONTENTS (Continued)4.2.3 Management Services 244.2.3.1 Configurati
20、on.254.2.3.2 Network Monitoring .254.2.3.3 Network Control 264.2.3.4 Intrinsic Maintenance 264.2.3.5 Invoked Maintenance264.2.3.6 RTCP Reset 265. USER/RTCP INTERFACE 275.1 Service Procedure.275.2 Service Primitives275.2.1 Request.275.2.2 Indication.275.2.3 Response285.2.4 Confirmation285.2.5 Instruc
21、tion285.3 Time Sequence Diagrams.285.4 Service Parameters.285.4.1 Service Topology.295.4.2 Quality of Service295.4.3 Results Reporting296. NOTES296.1 Key Words .29APPENDIX A TARGET APPLICATIONS KEY DESCRIPTOR WORDS30FIGURE 1 Aerospace Categories of RTCP Intended Applications .6FIGURE 2 RTCP System D
22、efinition 10FIGURE 3 Relationship Between Entities .10FIGURE 4 Definition of Topology Terms11FIGURE 5 Static Connections State Diagram .16FIGURE 6 Dynamic Connection State Diagram17FIGURE 7 Flow Control.20FIGURE 8 Types of Acknowledgements .22FIGURE 9 Types of Remote Interrupts24FIGURE 10 Sample Tim
23、e Sequence Diagram 29FIGURE A1 Key Descriptor Words 30Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-SAE AIR4886 - 5 -1. SCOPE:The purpose of this document is to establish the requirements for Real-Ti
24、me Communication Protocols (RTCP). Systems for real-time applications are characterized by the presence of hard deadlines where failure to meet a deadline must be considered a system fault.These requirements have been driven predominantly, but not exclusively, by aerospace type military platforms an
25、d commercial aircraft, but are generally applicable to any distributed, real-time, control systems. These requirements are primarily targeted for the Transport and Network Layers of peer to peer protocols, as referenced in the Open System Interconnect Reference Model (2.2.1 and 2.2.2), developed by
26、the International Standards Organization (ISO). These requirements are intended to complement SAE AS4074 (2.1.1) and AS4075 (2.1.2), and future SAE communications standards. Although information transfer objectives herein concentrate primarily on digital data flow attributes, efforts have been made
27、such as not to preclude sensor/video and voice information transfers. This document provides evaluation criteria for selecting viable alternatives for a real-time communications protocol standard.2. REFERENCES:The following publications form a part of this specification to the extent specified herei
28、n. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this specification and references cited herein, the text of this specification takes precedence
29、. Nothing in this specification, however, supersedes applicable laws and regulations unless a specific exemption has been obtained.2.1 SAE Publications:Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.2.1.1 AS407 Linear Token-Passing Multiplex Data Bus Standard2.1.2 AS4075 High
30、Speed Ring Bus Standard2.1.3 ARD50033 DRAFT Logical Interface Definition for Real-Time Communication Protocols (RTCP)2.2 U.S. Government Publications:Available from DODSSP, Subscription Services Desk, Building 4D, 700 Robbins Avenue, Philadelphia, PA 19111-5094.2.2.1 ISO 7498 Information Processing
31、Systems - Open Systems Interconnection - Basic Reference Model2.2.2 ISO 7498 Addendum 1: Connectionless-mode Transmission. Information Processing Systems - Open Systems Interconnection - Basic Reference Model.Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduc
32、tion or networking permitted without license from IHS-,-SAE AIR4886 - 6 -3. INTRODUCTION:The RTCP requirements set forth in this document, reflect a consensus of experts views for satisfying the needs of applications encompassing the entire field of aerospace military platforms and commercial aircra
33、ft. Nonaerospace applications are not precluded and will be encouraged to utilize the proposed RTCP standard. Aerospace categories of the RTCP intended applications are outlined in Figure 1.FIGURE 1 - Aerospace Categories of RTCP Intended Applications3.1 Target Applications Descriptions:The protocol
34、 requirements defined in this document are intended for real-time applications. Real-time applications, as defined here, are characterized by the presence of hard deadlines where failure to meet a deadline must be considered a system fault. While these applications are open in that they use publishe
35、d standards to ensure interoperability between equipment and across platforms, they are closed in the sense that valid users and transactions are predetermined during system design for a specific implementation.Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reprod
36、uction or networking permitted without license from IHS-,-SAE AIR4886 - 7 -3.1 (Continued):The following descriptors and characteristics of the intended target applications are based on a set of KEY DESCRIPTOR WORDS. These target application key descriptor words were developed by the Real-Time Model
37、 Task Group (RTMT) and they represent the consensus of this group. These key words and functional breakdown are included as Appendix A.3.1.1 Distributed: The RTMT target applications are distributed. This means that in addition to applications and processing being distributed, the following are also
38、 distributed: data, communications functions, control, storage, and system management functions.The characteristics of distributed data are many fold and include the following:a. Demand driven; that is, the data are sent when requested.b. Supply driven; that is, the data are sent at the time that th
39、e data are originated.c. For some data categories all data are essential, while for other categories only the latest data (or the latest N sets of data) are essential.d. For some data categories the integrity of the data is essential, while for other categories integrity is not a driving requirement
40、.e. For some categories of data, the order of arrival, or knowledge of the order of origination, is essential.f. Distributed data are of any size and of different data types (objects).The characteristics of the communication functions being distributed include the data transfer itself, packetization
41、 (the segmentation and reassembly of data), flow control and the routing to target destination(s) of the data.Characteristics of the control being distributed in these RTMT target applications include the following:a. The control of initiating execution of subsets of Application tasks on distributed
42、 resources.b. Provisions for the distribution of a global reference point, for synchronization purposes, and to allow time stamps on data, should that be desired.c. Provisions for remote interrupts.The characteristics of distributed storage imply that the target applications facilitate parallel data
43、 searches and stores, and need guaranteed data coherence (that is, the data stored must at any point in time appear consistent to all users).The implications of system management functions being distributed in these RTMT target applications include the following:a. Configurations; both static and dy
44、namic.b. Monitoring of system status, health and errors; the latter being either hard or intermittent.c. System state support; the global understanding of current system state, for instance, normal or exception states with degraded modes and changing system priorities and objectives.Copyright SAE In
45、ternational Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-SAE AIR4886 - 8 -3.1.2 Uninterrupted Operational Performance: The RTMT intended applications are characterized by requiring uninterrupted operational performance. This u
46、ninterrupted operational performance implies the tolerance of the occurrence of both scheduled and unscheduled events. The RTCP may take care of scheduled events either off-line (action taken in anticipation) or on-line (action taken reacting to the event).The unscheduled events may be either planne
47、d, such as interrupts or asynchronous events, or unplanned. The unscheduled unplanned events include both faults and defects.3.1.3 Real-Time: The RTMT intended applications are real-time systems. In this context real-time means that the systems are characterized by the presence of hard deadlines whe
48、re failure to meet a deadline must be considered a system fault.Real-time is a relative concept; timing parameters may vary from system to system. Requirements for each application specify the necessary deadlines, i.e., the acceptable response times.3.1.4 Highly Automated: The RTMT intended applicat
49、ions are characterized by many functions being automated. To be automated a function must be predefinable, that is, either via analytical methods or parametrically through behavioral models.3.1.5 Control: The RTMT intended applications may to a large extent be characterized by executing control functions. There are cause/reaction modes of system behavior. This implies closed loop(s) with cyclic data, and a fail saf
