1. www.ischool.drexel.edu INFO 203 IT for Engineers BACnet Dr. Jennifer Booker 1INFO 203 week 10

2. 2 Networking Review Detailed overview of computer networking introduced the layers of networking, their services, and their protocols –Application layer, home to the applications we use daily – HTTP, FTP, SMTP, POP3, IMAP, MIME; and DNS behind the scenes –Transport layer, home to TCP and UDP

3. Networking Review –Network layer, home to IPv4 and IPv6, plus routing protocols within an autonomous system (RIP, OSPF) and among them (BGP) –Link layer, home to Ethernet and PPP, plus the support protocol ARP –Physical layer, where protocols describe how to implement a link layer protocol over a particular medium (e.g. PPP over a copper wire) INFO 203 week 103

4. BACnet Now use this understanding of networking to investigate BACnet (Building Automation Control Network) to enable interoperability among building systems and devices BACnet was developed in 1987 by ASHRAE and first standardized in 1995 by ANSI and in 2003 (ISO 16484) ASHRAE INFO 203 week 104

5. BACnet BACnet can be based on Ethernet or IP networks, using a twisted pair link protocol MS/TP (see EIA-485) Object-oriented systems capture data and the functions they can use in objects –BACnet is object-oriented, and defines 54 standard objects that can be used or not independently of each other INFO 203 week 105

6. BACnet services BACnet provides a range of services –Object access –Alarm and event management –Scheduling –Trending –Files –Device and network management –Web services INFO 203 week 106

7. BACnet testing BACnet devices and applications are tested by the BACnet Testing Laboratory (BTL), in accordance with ASHRAE Standard 135.1 Applications include HVAC, fire, security, lighting, elevators, etc. INFO 203 week 107

8. Devices BACnet devices act as a controller, gateway, or user interface INFO 203 week 108

9. Objects INFO 203 week 109 Objects manage physical or logical information, e.g. analog or binary inputs, control algorithms, or other applications The 54 standard objects means many kinds of devices can be managed without developing new specific code for them –But non-standard objects are allowed

10. Objects INFO 203 week 1010 Objects define and object identifier and a collection of properties Properties may have read only or read/write ability, and can be required or optional

11. Services BACnet services are requests from one device to another –object access (read, write, create, delete); –device management (discover, time synchronization, initialize, backup and restore database); –alarm and event (alarms and changes of state); –file transfer (trend data, program transfer); –virtual terminal (human machine interface via prompts and menus). INFO 203 week 1011

12. Transport and Network BACnet allows several transport protocols BACnet can run over seven network types –IP (easy and fast but expensive) –MS/TP (Master-Slave/Token Passing) –Ethernet (if no IP routers are involved) –ARCNET (rarely used) –PPP (used only for dial-up connections) –LonTalk (passes messages only) –Zigbee (connect to local wireless devices) INFO 203 week 1012

13. Routing A major feature of BACnet is its ability to join many subnetworks together A BACnet router might join different BACnet networks from different network types –For example Broadcast Management Devices (BBMDs) are used to join BACnet/IP subnets INFO 203 week 1013

14. Interoperability The five areas of interoperability provided by BACnet are defined by the BACnet Interoperability Building Blocks (BIBBs): –Data sharing –Trending –Scheduling –Alarm & Event Management –Device & Network Management INFO 203 week 1014

15. Data Sharing Data can be sent uni- or bi-directionally between devices for archives, reports, sensor readings, control messages, or other purposes It uses a client-server model Read and Write properties are allowed –There are 16 levels of priority available for controlling writing to commandable objects INFO 203 week 1015

16. Data Sharing Data can also be shared via a Change of Value (COV) mode COV reduces network traffic by only reporting larger changes in data values on a subscribed device INFO 203 week 1016

17. Trending A Trend Log object collects data samples from devices Then a supervisory workstation reads the trend log periodically Helps cut down on network traffic INFO 203 week 1017

18. Scheduling Schedules can be maintained in devices to time controlling them Dates, times, day of week, week of month, and month can be used to manage schedules INFO 203 week 1018

19. Alarm & Event Management Data can be sent based on alarm limits or event triggers Logs and summaries can be generated INFO 203 week 1019

20. Device & Network Management This service allows detection of new devices (“device binding” based on network number and MAC address), objects within devices, establish communication, synchronize time, and reboot devices A process like ARP helps identify devices and objects automatically INFO 203 week 1020

21. Interoperability Conformity The Protocol Implementation and Conformance Statement (PICS) tells what BACnet features have been implemented in a particular device Based on BIBBs, which address the five interoperability areas already discussed Testing approved by BTL conforms to ASHRAE 135.1 INFO 203 week 1021

22. BACnet over IP (B/IP) ANSI/ASHRAE 135-1995 defines how BACnet works over IP-based networks We want B/IP devices to –Communicate with each other –Send and receive local broadcast messages –Receive global broadcast messages Devices have unique IP addresses but routers need to know a network number INFO 203 week 1022

23. B/IP Uses UDP because it’s already well known and doesn’t mean creating a new IP protocol code In a simple intranet, devices are identified by IP address and port number The link layer protocol is not specified INFO 203 week 1023

24. VLL BACnet defines a virtual link layer (BVLL) to help higher layers view BACnet consistently no matter what link protocol is actually used Devices communicate via unicast messages and the B/IP addresses –Broadcast messages are limited to the subnet not the regular IP broadcast address INFO 203 week 1024

25. Broadcast Broadcast messages are not routed to allow large B/IP networks without flooding traffic Consider IGMP (group management protocol) but instead create the BACnet Broadcast Management Device (BBMD) –Passes broadcast messages from one subnet to another; does little else INFO 203 week 1025

26. BBMD After rejecting star and ring architectures, BBMD was based on a fully connected star –All BBMDs are connected to all other BBMDs logically –Each BBMD must know the whole network architecture, and uses the same Broadcast Distribution Table (BDT) –There are BDT Read and Write messages INFO 203 week 1026

27. Foreign devices A foreign device has an IP address outside the B/IP subnet it wants to join, such as a dial-up connection via SLIP or PPP BBMDs use messages to register foreign devices and maintains a table of them –This foreign device table can be read and is then acknowledged –Can delete entries too INFO 203 week 1027

28. Foreign devices and networks BBMDs can forward broadcast messages to foreign devices and receive those messages from them too B/IP devices can IP devices outside of the BACnet, using the B/IP address to extract the IP and port number data needed Broadcast messages can also be sent to non B/IP networks or vice versa INFO 203 week 1028

29. Connecting B/IP networks Two or more B/IP networks can be joined Need to make sure device identifiers are unique across all networks (internetwork- wide) –Can often share a BACnet network number Must connect the networks with a BACnet router –The router is registered as a foreign agent on both/all networks INFO 203 week 1029

30. Connecting B/IP networks The same device can be a BBMD and BACnet router Within a B/IP router the ports are assigned B/IP network addresses Directly connected networks can receive local broadcast or multicast messages Other networks are considered ‘remote’ and are reached via a router INFO 203 week 1030

31. References Introductory material through slide 21 from http://bacnet.membershipsoftware.org/files/Homepage- Introduction%20to%20BACnet/BACnet%20Introduction %20-%20V3-1.pdf http://bacnet.membershipsoftware.org/files/Homepage- Introduction%20to%20BACnet/BACnet%20Introduction %20-%20V3-1.pdf Protocol details (slides 22-30) from http://www.bacnet.org/Tutorial/BACnetIP/index.html http://www.bacnet.org/Tutorial/BACnetIP/index.html INFO 203 week 1031