High Availability for Mission-Critical Connection


Having the client’s Wayside Interface Unit (WIU) on support, PSA continually performs improvements to ensure trouble-free and efficient operation, particularly on PTC-based railroads. To transfer mission-critical PTC data and manage interlockings, reliability and stability of the WIU PTC class D connection is required. To improve this connection, PSA needed to tweak the behavior of these systems to continue data transfer in case of failure.


Client Challenge

Enhance the reliability and security for connection between WIU and PTC systems in case of failures.

Project Objective

Implement the high availability (HA) functionality for WIU and PTC systems to communicate seamlessly.


The PSA engineering team developed a software solution that allows system nodes to instantly utilize alternate addresses and ports to recover from a link or node failure. We set new rules for Class D nodes' behavior in compliance with all requirements of the protocol layer. 

Instead of one alternate link negotiated initially, we added multiple links to switch to in case of failure, as a result of a client project change request. For this, we reworked and refactored the current Class D protocol layer implementation. In general, PSA provided extended functionality on the following components: 

  • System updates related to both WIU and management tools including:

        •  new configuration parameters in Linux ITCSM and SMShell;

        •  high availability functionality in Class D protocol;

        •  displaying the currently used IP.

  • Web interface implementation, including updates for web page design and business logic, adding new fields, validation functionality for fields, handling of the new HA parameters, and displaying of current IP. 

  • Adjustments for WIU application builder, including GUI, and adding high availability parameters.

To confirm the operability of the updated system, we performed both engineering testing for each component and functional testing to check if the entire system behaves correctly.

To explore more technical details click here.

Development Included

  • Requirements clarification
  • Implementation activities
  • UI Updates
  • Functional testing
  • Engineering testing



  • More reliable and secure WIU PTC connection

Technology Breakdown

Project size
  • 1 person
  • 7 months

Further Cooperation

Check out other PSA WIU-related projects, such as PTC wayside system management and PTC secure communication system

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