ISO/FDIS 16484-5

Building automation and control systems (BACS) — Part 5: Data communication protocol

The purpose of this document is to define data communication services and protocols for computer equipment used for monitoring and control of HVAC&R and other building systems and to define, in addition, an abstract, object-oriented representation of information communicated between such equipment, thereby facilitating the application and use of digital control technology in buildings.

Systèmes d'automatisation et de gestion technique du bâtiment (BACS) — Partie 5: Protocole de communication de données

L'objectif de cette norme est de définir des services et des protocoles de communication de données pour les équipements informatiques utilisés pour la surveillance et le contrôle des systèmes CVC&R et d'autres systèmes de bâtiment et de définir, en outre, une représentation abstraite et orientée objet des informations communiquées entre ces équipements, facilitant ainsi l'application et l'utilisation de la technologie de contrôle numérique dans les bâtiments.

General Information

• Status: Not Published
• ICS: 35.240.67 - IT applications in building and construction industry
• ICS: 91.040.01 - Buildings in general
• Technical Committee: ISO/TC 205 - Building environment design
• Drafting Committee: ISO/TC 205/WG 3 - Building Automation and Control System (BACS) Design
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 02-Apr-2026
• Completion Date: 02-Apr-2026

Relations

• Consolidates: prEN ISO 16484-5 - Building automation and control systems (BACS) - Part 5: Data communication protocol (ISO/FDIS 16484-5:2026)
• Effective Date: 12-Feb-2026
• Revises: ISO 16484-5:2022 - Building automation and control systems (BACS) — Part 5: Data communication protocol
• Effective Date: 17-May-2025

Overview

ISO/FDIS 16484-5:2026, Building automation and control systems (BACS) - Part 5: Data communication protocol, defines the essential data communication services and protocols required for effective monitoring and control of building automation systems. This international standard, developed by ISO/TC 205, provides a comprehensive framework for integrating computer equipment in the management of HVAC&R (Heating, Ventilation, Air Conditioning, and Refrigeration) as well as other building systems.

A central focus of ISO 16484-5 is its specification of an object-oriented representation for information exchange. This advances digital control technology in buildings by promoting interoperability and standardizing communications between diverse devices.

Key Topics

• BACnet Protocol Architecture:
  The standard details the structure of the BACnet communication protocol, including its network topology and security features.

• Layered Communication Model:
  ISO 16484-5 addresses the application, network, and data link/physical layers, supporting multiple LAN types (Ethernet, ARCNET, MS/TP, PTP, LonTalk) for flexible deployment.

• Information Modeling:
  Control devices are modeled as collections of objects, enabling a consistent and abstract method for representing device capabilities and data.

• Service Specifications:
  Comprehensive service definitions cover alarm/event management, file access, object access, device management, and remote communications.

• Security and Access:
  Provisions for authentication and authorization help secure building automation network communications.

• Interoperability and Conformance:
  Detailed requirements support vendor-neutral integration and extension for proprietary adaptations, fostering a robust ecosystem of compatible devices.

Applications

ISO 16484-5 is widely adopted in the design, implementation, and operation of building automation and control systems. Its versatility supports a broad range of practical applications, including:

• HVAC&R System Management:
  Coordinated control and monitoring of heating, ventilation, air conditioning, and refrigeration systems for improved energy efficiency and occupant comfort.

• Lighting and Access Control:
  Integration of lighting control, security, and access management across multiple vendors and subsystems.

• Facility Integration:
  Connecting disparate automation equipment in commercial, industrial, and institutional buildings, centralizing the monitoring and control functions.

• Scalability and Upgrades:
  Standardized communication protocols ease system expansion, future retrofits, and technology upgrades without vendor lock-in.

• Remote Operation and Analytics:
  Enabling remote device management, performance analytics, and alarm/event processing for smarter building operation.

Related Standards

For a holistic approach to building automation, ISO 16484-5 is aligned with several related international standards, enhancing its value and application:

• ISO 16484-1: Building automation and control systems - Overview and definitions
• ISO 16484-2: Building automation and control systems - Hardware
• ISO 16484-3: Building automation and control systems - Functions
• ISO/IEC 14908.1: Controls networks - Protocol stack
• ISO 8802-3: Local area networks - Carrier sense multiple access with collision detection (Ethernet)

Summary

ISO/FDIS 16484-5:2026 is the definitive international standard for data communication protocols in building automation and control systems. By providing a clear framework for interoperable, secure, and scalable device communications, it plays a vital role in the effective digital management of modern building systems. Its adoption ensures compliance, promotes vendor neutrality, and supports the ongoing development of intelligent, energy-efficient buildings.

Standards Content (Sample)

FINAL DRAFT
International
Standard
ISO/TC 205
Building automation and control
Secretariat: ANSI
systems (BACS) —
Voting begins on:
Part 5:
2026-04-02
Data communication protocol
Voting terminates on:
Systèmes de contrôle et d'automatisation des bâtiments
(BACS) —
2026-05-28
Partie 5: Protocole de communication de données
This document is circulated as received from the committee secretariat.
FAST TRACK PROCEDURE
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ii
CONTENTS
Foreword . xi
FOREWORD . xii
1 PURPOSE . 1
2 SCOPE . 1
3 DEFINITIONS . 1
3.1 Terms Adopted from International Standards . 1
3.2 Terms Defined for this Standard . 2
3.3 Abbreviations and Acronyms Used in this Standard . 8
4 BACnet PROTOCOL ARCHITECTURE. 12
4.1 The BACnet Collapsed Architecture . 13
4.2 BACnet Network Topology . 15
4.3 Security . 16
5 THE APPLICATION LAYER . 17
5.1 The Application Layer Model . 17
5.2 Segmentation of BACnet Messages . 23
5.3 Transmission of BACnet APDUs . 24
5.4 Application Protocol State Machines . 28
5.5 Application Protocol Time Sequence Diagrams . 46
5.6 Application Layer Service Conventions . 55
6 THE NETWORK LAYER . 57
6.1 Network Layer Service Specification . 57
6.2 Network Layer PDU Structure. 59
6.3 Messages for Multiple Recipients . 65
6.4 Network Layer Protocol Messages . 65
6.5 Network Layer Procedures . 69
6.6 BACnet Routers . 71
6.7 Point-To-Point Half-Routers . 76
7 DATA LINK/PHYSICAL LAYERS: Ethernet (ISO 8802-3) LAN . 81
7.1 The Use of ISO 8802-2 Logical Link Control (LLC) . 81
7.2 Parameters Required by the LLC Primitives . 81
7.3 Parameters Required by the MAC Primitives . 81
7.4 Physical Media . 81
8 DATA LINK/PHYSICAL LAYERS: ARCNET (ATA 878.1) LAN . 82
8.1 The Use of ISO 8802-2 Logical Link Control (LLC) . 82
8.2 Parameters Required by the LLC Primitives . 82
8.3 Mapping the LLC Services to the ARCNET MAC Layer . 82
8.4 Parameters Required by the MAC Primitives . 82
8.5 Physical Media . 82
9 DATA LINK/PHYSICAL LAYERS: MULTIDROP SERIAL BUS/TOKEN PASSING (MS/TP) LAN . 84
9.1 Service Specification . 84
9.2 Physical Layer . 86
9.3 MS/TP Frame Format . 96
9.4 Overview of the MS/TP Network . 98
9.5 MS/TP Medium Access Control . 99
9.6 Cyclic Redundancy Check (CRC) . 120
9.7 Interfacing MS/TP LANs with Other BACnet LANs . 121
9.8 Responding BACnet User Processing of Messages from MS/TP . 121
9.9 Repeaters . 122
9.10 COBS (Consistent Overhead Byte Stuffing) Encoding . 123
9.11 Documenting MS/TP Node Design Choices . 127
10 DATA LINK/PHYSICAL LAYERS: POINT-TO-POINT (PTP) . 128
10.1 Overview . 128
10.2 Service Specification . 128
10.3 Point-to-Point Frame Format . 133
iii
10.4 PTP Medium Access Control Protocol . 135
11 DATA LINK/PHYSICAL LAYERS: LonTalk (ISO/IEC 14908.1) LAN . 157
11.1 The Use of ISO 8802-2 Logical Link Control (LLC) . 157
11.2 Parameters Required by the LLC Primitives . 157
11.3 Mapping the LLC Services to the LonTalk Application Layer. 157
11.4 Parameters Required by the Application Layer Primitives . 157
11.5 Physical Media . 158
12 MODELING CONTROL DEVICES AS A COLLECTION OF OBJECTS . 160
12.1 Object Characteristics and Requirements . 160
12.2 Analog Input Object Type . 167
12.3 Analog Output Object Type . 174
12.4 Analog Value Object Type . 182
12.5 Averaging Object Type . 190
12.6 Binary Input Object Type . 194
12.7 Binary Output Object Type . 201
12.8 Binary Value Object Type . 210
12.9 Calendar Object Type . 218
12.10 Command Object Type . 221
12.11 Device Object Type . 228
12.12 Event Enrollment Object Type . 244
12.13 File Object Type . 253
12.14 Group Object Type . 257
12.15 Life Safety Point Object Type . 260
12.16 Life Safety Zone Object Type. 268
12.17 Loop Object Type . 276
12.18 Multi-state Input Object Type . 286
12.19 Multi-state Output Object Type . 292
12.20 Multi-state Value Object Type. 299
12.21 Notification Class Object Type . 307
12.22 Program Object Type . 313
12.23 Pulse Converter Object Type . 320
12.24 Schedule Object Type . 328
12.25 Trend Log Object Type . 336
12.26 Access Door Object Type . 347
12.27 Event Log Object Type . 357
12.28 Load Control Object Type . 365
12.29 Structured View Object Type . 376
12.30 Trend Log Multiple Object Type . 381
12.31 Access Point Object Type . 391
12.32 Access Zone Object Type . 409
12.33 Access User Object Type . 418
12.34 Access Rights Object Type . 422
12.35 Access Credential Object Type . 429
12.36 Credential Data Input Object Type . 439
12.37 CharacterString Value Object Type . 446
12.38 DateTime Value Object Type . 453
12.39 Large Analog Value Object Type . 459
12.40 BitString Value Object Type . 467
12.41 OctetString Value Object Type . 474
12.42 Time Value Object Type . 479
12.43 Integer Value Object Type . 485
12.44 Positive Integer Value Object Type . 493
12.45 Date Value Object Type . 501
12.46 DateTime Pattern Value Object Type . 507
12.47 Time Pattern Value Object Type . 513
12.48 Date Pattern Value Object Type . 519
12.49 Deleted Clause . 525
iv
12.50 Global Group Object Type . 526
12.51 Notification Forwarder Object Type . 534
12.52 Alert Enrollment Object Type . 542
12.53 Channel Object Type . 546
12.54 Lighting Output Object Type . 557
12.55 Binary Lighting Output Object Type . 575
12.56 Network Port Object Type . 587
12.57 Timer Object Type . 629
12.58 Elevator Group Object Type . 642
12.59 Lift Object Type . 646
12.60 Escalator Object Type . 659
12.61 Accumulator Object Type . 667
12.62 Staging Object Type . 677
12.63 Audit Reporter Object Type. 688
12.64 Audit Log Object Type . 694
12.65 Color Object Type . 701
12.66 Color Temperature Object Type . 707
13 ALARM AND EVENT SERVICES . 714
13.1 Change of Value Reporting . 714
13.2 Event Reporting . 719
13.3 Event Algorithms . 732
13.4 Fault Algorithms . 764
13.5 AcknowledgeAlarm Service . 772
13.6 ConfirmedCOVNotification Service . 774
13.7 UnconfirmedCOVNotification Service. 776
13.8 ConfirmedEventNotification Service . 777
13.9 UnconfirmedEventNotification Service . 780
13.10 GetAlarmSummary Service . 783
13.11 GetEnrollmentSummary Service . 785
13.12 GetEventInformation Service . 788
13.13 LifeSafetyOperation Service . 791
13.14 SubscribeCOV Service . 793
13.15 SubscribeCOVProperty Service . 796
13.16 SubscribeCOVPropertyMultiple Service . 799
13.17 ConfirmedCOVNotificationMultiple Service . 805
13.18 UnconfirmedCOVNotificationMultiple Service . 808
13.19 AuditLogQuery . 810
13.20 ConfirmedAuditNotification . 814
13.21 UnconfirmedAuditNotification . 815
14 FILE ACCESS SERVICES . 816
14.1 AtomicReadFile Service . 816
14.2 AtomicWriteFile Service . 819
15 OBJECT ACCESS SERVICES . 822
15.1 AddListElement Service . 822
15.2 RemoveListElement Service . 825
15.3 CreateObject Service . 827
15.4 DeleteObject Service . 830
15.5 ReadProperty Service . 831
15.6 Deleted Clause . 833
15.7 ReadPropertyMultiple Service . 834
15.8 ReadRange Service . 837
15.9 WriteProperty Service . 845
15.10 WritePropertyMultiple Service . 848
15.11 WriteGroup Service . 851
16 REMOTE DEVICE MANAGEMENT SERVICES . 853
16.1 DeviceCommunicationControl Service . 853
16.2 ConfirmedPrivateTransfer Service . 855
v
16.3 UnconfirmedPrivateTransfer Service . 857
16.4 ReinitializeDevice Service . 858
16.5 ConfirmedTextMessage Service . 860
16.6 UnconfirmedTextMessage Service . 862
16.7 TimeSynchronization Service . 863
16.8 UTCTimeSynchronization Service . 864
16.9 Who-Has and I-Have Services . 865
16.10 Who-Is and I-Am Services . 867
16.11 Who-Am-I and You-Are Services . 869
17 AUTHENTICATION AND AUTHORIZATION SERVICES . 872
17.1 Overview . 872
17.2 Trust of Intermediaries . 873
17.3 Authentication . 874
17.4 Authorization . 876
17.5 Conformance Requirements. 882
17.6 AuthRequest Service. 883
18 ERROR, REJECT, and ABORT CODES . 887
18.1 Error Class - DEVICE . 887
18.2 Error Class - OBJECT . 887
18.3 Error Class - PROPERTY . 888
18.4 Error Class - RESOURCES . 890
18.5 Error Class - SECURITY . 890
18.6 Error Class - SERVICES . 892
18.7 Error Class - COMMUNICATION . 893
18.8 Error Class - VT . 898
18.9 Reject Reason . 898
18.10 Abort Reason . 899
18.11 Confirmed Service Common Errors . 900
19 BACnet PROCEDURES . 901
19.1 Backup and Restore . 901
19.2 Command Prioritization . 906
19.3 Device Restart Procedure . 911
19.4 Determining Maximum Conveyable APDU . 912
19.5 Value Source Mechanism . 914
19.6 Audit Logging . 916
19.7 Unconfigured Device Discovery and Address Assignment . 927
19.8 Replacing Certificates in a BACnet/SC Network . 928
19.9 Device Address Proxying . 930
20 ENCODING BACnet PROTOCOL DATA UNITS . 934
20.1 Encoding the Fixed Part of BACnet APDUs . 935
20.2 Encoding the Variable Part of BACnet APDUs . 947
21 FORMAL DESCRIPTION OF APPLICATION PROTOCOL DATA UNITS . 963
21.1 APDU Definitions . 963
21.2 Confirmed Service Productions . 965
21.3 Unconfirmed Service Productions . 976
21.4 Error Productions . 980
21.5 Application Types . 992
21.6 Base Types . 994
22 CONFORMANCE AND INTEROPERABILITY . 1082
22.1 Conformance to BACnet . 1082
22.2 BACnet Interoperability . 1083
23 EXTENDING BACnet TO ACCOMMODATE VENDOR PROPRIETARY INFORMATION. 1085
23.1 Extending Enumeration Values . 1085
23.2 Using the PrivateTransfer Services to Invoke Non-Standardized Services . 1086
23.3 Adding Proprietary Properties to a Standardized Object . 1086
23.4 Adding Proprietary Object Types to BACnet . 1087
23.5 Restrictions on Extending BACnet . 1087
vi
24 DELETED CLAUSE . 1088
25 REFERENCES . 1089
ANNEX A - PROTOCOL IMPLEMENTATION CONFORMANCE STATEMENT (NORMATIVE) . 1094
ANNEX B - GUIDE TO SPECIFYING BACnet DEVICES (INFORMATIVE) . 1098
ANNEX C - Removed . 1099
ANNEX D - Removed . 1100
ANNEX E - EXAMPLES OF BACnet APPLICATION SERVICES (INFORMATIVE) . 1101
E.1 Alarm and Event Services . 1101
E.2 File Access Services . 1106
E.3 Object Access Services . 1107
E.4 Remote Device Management Services . 1114
E.5 Virtual Terminal Services . 1117
ANNEX F - EXAMPLES OF APDU ENCODING (INFORMATIVE) . 1120
F.1 Example Encodings for Alarm and Event Services . 1120
F.2 Example Encodings for File Access Services . 1131
F.3 Example Encodings for Object Access Services . 1134
F.4 Example Encodings for Remote Device Management Services . 1144
F.5 Example Encodings for Virtual Terminal Services . 1150
ANNEX G - CALCULATION OF CRC (INFORMATIVE) . 1153
G.1 Calculation of the Header CRC . 1153
G.2 Calculation of the Data CRC . 1159
G.3 Calculation of the Encoded CRC-32K . 1163
ANNEX H - COMBINING BACnet NETWORKS WITH NON-BACnet NETWORKS (NORMATIVE) . 1167
H.1 BACnet Gateways . 1167
H.2 Requirements and Best Practices for BACnet Gateway Implementations . 1167
H.3 Using BACnet with the DARPA Internet Protocols . 1169
H.4 Using BACnet with the IPX Protocol . 1171
H.5 Using BACnet with EIB/KNX . 1172
H.6 Using BACnet with the Former BACnet/WS Web Services Interface Defined by Annex N . 1182
H.7 Virtual MAC Addressing . 1183
ANNEX I - COMMANDABLE PROPERTIES WITH MINIMUM ON AND OFF TIMES (INFORMATIVE) . 1185
ANNEX J - BACnet/IP (NORMATIVE) . 1187
J.1 General . 1187
J.2 BACnet Virtual Link Layer.
...

PROJET FINAL
Norme
internationale
ISO/TC 205
Systèmes d'automatisation et de
Secrétariat: ANSI
gestion technique du bâtiment
Début de vote:
(BACS) —
2026-04-02
Partie 5:
Vote clos le:
2026-06-25
Protocole de communication de
données
Building automation and control systems (BACS) —
Part 5: Data communication protocol
Le présent document est distribué tel qu’il est parvenu du secrétariat
du comité.
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS,
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AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À
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FOURNIR UNE DOCUMENTATION EXPLICATIVE.
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DU POINT DE VUE DE LEUR POSSI BILITÉ DE DEVENIR DES
NORMES POUVANT
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NATIONALE.
Numéro de référence
PROJET FINAL
Norme
internationale
ISO/TC 205
Systèmes d'automatisation et de
Secrétariat: ANSI
gestion technique du bâtiment
Début de vote:
(BACS) —
2026-04-02
Partie 5:
Vote clos le:
2026-06-25
Protocole de communication de
données
Building automation and control systems (BACS) —
Part 5: Data communication protocol
Ce document n’a pas été rédigé par le Secrétariat central de l’ISO.
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS,
NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS
DOCUMENT PROTÉGÉ PAR COPYRIGHT AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À
FAST TRACK PROCEDURE
FOURNIR UNE DOCUMENTATION EXPLICATIVE.
OUTRE LE FAIT D’ÊTRE EXAMINÉS POUR
© ISO 2026
ÉTABLIR S’ILS SONT ACCEPTABLES À DES FINS
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INDUSTRIELLES, TECHNOLOGIQUES E
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