Message-Based Communications for Pipeline SCADA
Stephen Koenig, P.E.
Smarter Infrastructure for Oil and Gas
December 3, 2013Houston, TX
source: http://www.epa.gov/gasstar/images/newsroom/fall11-valve.jpg
source: http://www.transport4.com/PublicSite/t4publicweb/home.aspx
Data stored in the meter station Flow Computer
Sensor Data
Data stored in the Corporate Accounting System
Data calculatedby meter stationFlow Computer
Messaging - Basic Concepts
• Multiple data sources (publishers) send messages to multiple data destinations (subscribers)
• Destinations subscribe by “topic”
• Payload can be anything: text, binary, fixed fields, etc up to 250Mbytes in size
• Broker supports multiple delivery options (QoS)
Data Destination
Data Destination
Data Destination
Data Source
Data Source
Data Source
Network
Message Broker
Data Source
Data Destination
Publish Subscribe
Message Format
Topic Payload
Automation to SupportPipeline Operations
F
TP
FlowComputer
RemoteTerminal
Unit
CommProcessor
TankGaugingSystem
SatelliteLink to ControlCenter
source: http://www.northerngateway.ca/assets/498x245_contentimages/EnvironmenatlResponsibility/Pipelineassesment.jpg
Traditional Approach to SCADA Poll/Response
• Host & RTU’s are serial devices – typically Programmable Logic Controllers
• “Round Robin” polling
• Data format optimized for mininimum overhead
Problems with Poll/Response systems
• Host “owns” communications link
• Dedicated circuits are too expensive
• Alarm latency increases with RTU count
Challenges in Use of Message-BasedCommunications for SCADA
• Controls – limited life in system• Stale Data – replace poll/response
functionality in event-driven system• Security
– Flexible architecture may result in new vulnerabilities
– Message-based system must be as secure as traditional poll/response
– Need for continuous improvement
Benefits of Message-Based Approach to SCADA
• Topic/Payload Message Structure• IP Routing• Intelligent Front-End Processor• Many-to-Many Architecture
Benefits - Topic/Payload Message Structure
• “Wildcard” subscriptions
•Support for multiple applications on one message broker
• Use of version number in topic
- Facilitate prototype and test of new clients
- Allows site-by-site migration strategy
Benefits – IP Routing -- Redundancy Reducing the Impact of Failure
• Provisions for broker equipment failure
• Provisions for loss of primary communications link – backup link
Broker1Broker2Broker3Broker4
Benefits – Intelligent Front-End Processor
• Adapt Serial Devices to IP/VSAT
• Move polling/response to field
• Ability to handle multiple RTU protocols
• Local intelligence can supplement or enhance control system
Broker1Broker2Broker3Broker4
Benefits – Many-to-Many Architecture
• Significantly reduced project schedules
• Off-line systems receive live data for testing