Requirements Engineering for Wayside Interface Unit Executive Software


In 2018, our client, a global railway player, started upgrading activities for North American railroads aiming to improve their reliability and performance. The vital part of that upgrade was the implementation of the advanced wayside interface unit with the vital processor (CPU) for signaling and PTC applications that allows greater reliability, performance, flexibility, enhanced communications, monitoring, and diagnostics capabilities. To launch the modernized systems, the WIU had to be certified, which was not possible due to the lack of formalized requirements documentation.


Client Challenge

Accelerate the launch of advanced signaling applications that utilize processing units with greater performance, flexibility, and diagnostics capabilities.

Project Objective

Assist in obtaining certification for the advanced WIU by providing comprehensive software requirements.


To prepare requirements, our team performed reverse engineering of the source code of the provided software modules – its program elements. The task was to analyze every software module and corresponding design specification to re-engineer requirements to the functions they performed. The provided modules were responsible for different areas of WIU functionality, such as Application Logic processing, Hot Standby, System Executive, and Configuration components.

Since the source code did not completely reflect the specifications, we needed to offset this in our requirements so that documents do not contradict each other.

With strict adherence to descriptive and terminological standards, we delivered requirements to the 2 pilot modules and then completed the whole scope. The requirements had defined the vital and non-vital system functions, confirming support of basic and advanced applications, such as:

  • Various types of interlockings

  • Interfaces to field devices

  • Warm and hot-standby

  • Train detection

  • CBTC support, etc.

As a result, our client received 25 comprehensive requirements documents that include purposes, constraints, and functional requirements for every provided module.

To explore more technical details click here.

Development Included

  • Existing Software and Design Specifications Review and Analysis
  • Requirements Documentation Creation



  • Requirements documentation for 25 software modules

  • Brand-new WIU certified for rail applications on time

  • Modernization activities for North American railroads were launched

Technology Breakdown

Project size
  • 3 people
  • 7 months

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