Telecom Billing Modernization: Extracting 5G Subscription Logic from Legacy Mainframes

The telecommunications industry is currently trapped in a "5G Paradox": carriers are marketing ultra-low latency and dynamic network slicing while their core Business Support Systems (BSS) still run on COBOL-based mainframes designed during the era of landlines. As service providers attempt to launch complex 5G monetization models—incorporating IoT density, edge computing, and tiered latency—they find that telecom billing modernization extracting efforts are hitting a wall of undocumented legacy code.

According to Replay’s analysis, the average enterprise rewrite of a core billing module takes 18 months, yet 70% of these legacy rewrites either fail entirely or exceed their original timelines by over 100%. The friction isn't just in the code; it’s in the institutional knowledge that has evaporated over decades.

TL;DR: Legacy telecom billing systems are the primary bottleneck for 5G ROI. Manual extraction of business logic from green screens takes 40+ hours per screen and carries a high risk of failure. Replay uses Visual Reverse Engineering to convert recorded legacy workflows into documented React components and Design Systems, reducing modernization timelines from years to weeks and saving up to 70% in engineering costs.

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The $3.6 Trillion Crisis in Telecom Infrastructure#

The global technical debt has ballooned to $3.6 trillion, and nowhere is this more visible than in the telecommunications sector. For a Tier-1 carrier, the billing system is the "Source of Truth," but it is often a "Black Box."

Industry experts recommend that telecom billing modernization extracting of logic should begin not with the database schema, but with the user workflows that have successfully processed billions of dollars in revenue for decades. The problem is that 67% of these legacy systems lack any form of current documentation. When a developer is asked to move a 5G subscription logic from a mainframe to a cloud-native microservice, they aren't just writing code; they are performing digital archaeology.

Why Manual Extraction is a Failing Strategy#

Traditionally, modernization involves "Screen Scraping" or manual "Code Harvesting." This requires senior architects to sit with subject matter experts (SMEs) to document every "If-Then" statement hidden behind a 3270 terminal emulator.

1. •The Documentation Gap: Most SMEs who understood the original logic have retired.
2. •The Time Sink: Manual documentation takes an average of 40 hours per screen.
3. •The Logic Drift: What is written in the COBOL source often differs from how the UI actually handles edge cases in production.

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Visual Reverse Engineering: A New Path for Telecom Billing Modernization Extracting#

Visual Reverse Engineering is the process of recording real-time user interactions with legacy software to automatically generate modern codebases, architectural flows, and comprehensive documentation.

Instead of reading 50,000 lines of COBOL to understand how a 5G data cap is calculated, Replay allows engineers to simply record the workflow. The platform analyzes the visual changes, state transitions, and data inputs to produce a functional React component that mirrors the legacy logic but uses modern architecture.

Definition: Video-to-code is the process of converting screen recordings of legacy software applications into structured, production-ready frontend code and design tokens using AI-driven computer vision and static analysis.

Comparing Modernization Approaches#

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The Technical Challenge: Extracting 5G Slicing Logic#

5G introduces "Network Slicing," where a single physical network is partitioned into multiple virtual networks. Billing for this requires a level of granularity that legacy mainframes weren't built for. When telecom billing modernization extracting logic for these slices, developers must account for:

• •Dynamic QoS (Quality of Service) parameters.
• •Real-time usage triggers across edge nodes.
• •Multi-partner settlement logic.

When you use Replay, the platform captures these complex state transitions. For example, if a billing clerk enters a specific override code for a high-priority "Healthcare Slice," Replay identifies that logic branch and encapsulates it into a reusable React hook or component.

Example: From Green Screen to React Component#

Below is a representation of how a legacy billing "Plan Override" screen is transformed into a modern TypeScript component using Replay’s automation suite.

typescript
// Generated by Replay AI Automation Suite
// Source: Legacy Mainframe BSS - Screen ID: BILL-REF-502

import React, { useState, useEffect } from 'react';
import { Button, Input, Card, Alert } from '@/components/ui-library';

interface SubscriptionLogicProps {
  subscriberId: string;
  currentSlice: 'Standard' | 'Premium' | 'Ultra-Low-Latency';
  onUpdate: (newPlan: string) => void;
}

export const PlanModernizationModule: React.FC<SubscriptionLogicProps> = ({
  subscriberId,
  currentSlice,
  onUpdate
}) => {
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);

  // Replay extracted this logic from the "PF3" key function in the legacy UI
  const handleSliceUpgrade = async (targetSlice: string) => {
    setLoading(true);
    try {
      // Logic mirrored from legacy COBOL 'UPDATE-SLICE-PROC'
      const response = await updateSubscription(subscriberId, targetSlice);
      if (response.success) {
        onUpdate(targetSlice);
      }
    } catch (err) {
      setError("Mainframe Sync Error: Check 5G Core Connectivity");
    } finally {
      setLoading(false);
    }
  };

  return (
    <Card className="p-6 border-l-4 border-blue-600">
      <h3>5G Subscription Management</h3>
      <p>Current Slice: <strong>{currentSlice}</strong></p>
      {error && <Alert variant="destructive">{error}</Alert>}
      <div className="flex gap-4 mt-4">
        <Button 
          disabled={loading} 
          onClick={() => handleSliceUpgrade('Ultra-Low-Latency')}
        >
          Upgrade to ULL Slice
        </Button>
      </div>
    </Card>
  );
};

This code isn't just a "look-alike." Because it was generated via Visual Reverse Engineering, the state management (the way the UI reacts to data) is functionally identical to the legacy system that has been proven stable for decades.

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Overcoming the "Documentation Debt" in BSS#

One of the greatest hurdles in telecom billing modernization extracting is the lack of a centralized Design System. Legacy systems often have "hidden" UI elements—fields that only appear when a specific combination of keys is pressed.

Replay’s Library feature solves this by automatically identifying recurring UI patterns across thousands of legacy screens. It extracts colors, typography, and component structures to build a modern Design System in Figma and React simultaneously.

Industry experts recommend that carriers stop trying to "document the past" and start "recording the present." By recording actual workflows of billing analysts, Replay creates a living blueprint of the system architecture.

Learn more about modernizing without rewriting from scratch

Building the 5G Blueprint#

In the Replay Blueprints editor, architects can see a visual map of how data flows from a 5G cell tower signal into a line item on a PDF invoice. This "Flow" view is critical for telecom billing modernization extracting because it reveals dependencies that are often invisible in the source code.

typescript
// Example of an extracted architectural flow state
// This defines how the 5G billing 'Flow' transitions between states

export const BillingFlowMap = {
  initial: 'IDLE',
  states: {
    IDLE: {
      on: { START_BILLING_RUN: 'VALIDATING_SUBSCRIBER' }
    },
    VALIDATING_SUBSCRIBER: {
      on: { 
        SUCCESS: 'CALCULATING_5G_USAGE',
        FAILURE: 'EXCEPTION_LOG' 
      }
    },
    CALCULATING_5G_USAGE: {
      invoke: {
        src: 'fetchUsageData',
        onDone: 'APPLYING_SLICE_TARIFFS'
      }
    },
    APPLYING_SLICE_TARIFFS: {
      // This specific logic was extracted from the legacy 'TARIFF-CALC-MOD'
      entry: ['calculateTaxes', 'applyPromotions'],
      on: { COMPLETE: 'GENERATING_INVOICE' }
    }
  }
};

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Security and Compliance in Regulated Telecom Environments#

Telecom is a highly regulated industry. Any tool used for telecom billing modernization extracting must meet stringent security standards. Mainframe data often contains Sensitive Personal Information (SPI) and Proprietary Network Guest Information (CPNI).

Replay is built for these environments:

• •SOC2 & HIPAA-ready: Ensuring data integrity and privacy.
• •On-Premise Availability: For carriers who cannot allow data to leave their internal network, Replay can be deployed entirely behind the firewall.
• •AI Automation Suite: The AI components are designed to work with obfuscated data, ensuring that the logic is extracted without ever exposing actual subscriber PII.

Discover Replay's Enterprise Security Features

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The Financial Case: 40 Hours vs. 4 Hours#

The math behind telecom billing modernization extracting is simple but devastating for those using manual methods. To modernize a typical enterprise BSS suite with 500 critical screens:

• •Manual Method: 500 screens x 40 hours/screen = 20,000 engineering hours. At $150/hr, that's $3,000,000 just for the extraction phase.
• •Replay Method: 500 screens x 4 hours/screen = 2,000 engineering hours. At $150/hr, that's $300,000.

By saving 90% of the time in the discovery and extraction phase, telecom companies can reallocate their best talent to building new 5G features rather than documenting 30-year-old COBOL.

Read about reducing technical debt in the enterprise

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Implementing the "Extract-Transform-Modernize" Workflow#

To successfully execute telecom billing modernization extracting, we recommend a three-phase approach:

1. The Recording Phase (Discovery)#

Subject matter experts record their daily billing workflows using Replay. They cover standard 5G plan activations, complex enterprise billing adjustments, and edge-case error handling.

2. The Extraction Phase (Reverse Engineering)#

Replay’s AI Automation Suite processes the videos. It identifies the "Flows" (the business logic) and the "Library" (the UI components). The output is a set of documented React components and a clear architectural map of the legacy system.

3. The Modernization Phase (Implementation)#

Developers use the generated code as a foundation. Instead of starting from a blank screen, they are 70% of the way to a finished product. They refine the React components, connect them to new cloud-native APIs (like AWS or Azure Telco Cloud), and deploy.

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Frequently Asked Questions#

Does Replay require access to our mainframe source code?#

No. Replay uses Visual Reverse Engineering, which means it analyzes the output and behavior of the application as seen on the screen. This is particularly valuable for telecom billing modernization extracting when the original source code is lost, undocumented, or too complex to parse manually.

How does Replay handle complex 5G billing logic that isn't visible on the screen?#

While Replay captures everything visible in the UI, it also identifies the state changes and data patterns that imply underlying logic. By recording multiple variations of a workflow, Replay can map out the conditional logic (e.g., "If User is in Zone A, then Tax Rate is X") that governs the system.

Can Replay generate code in frameworks other than React?#

Currently, Replay is optimized for React and TypeScript to ensure the highest quality of the generated Design Systems and Component Libraries. This aligns with the industry standard for modernizing BSS/OSS frontends in the telecom sector.

Is Visual Reverse Engineering faster than traditional "Screen Scraping"?#

Significantly. Traditional screen scraping merely puts a "web skin" over an old system, keeping the legacy technical debt alive. Telecom billing modernization extracting with Replay actually generates new, independent code and documentation, allowing you to eventually shut down the mainframe entirely.

How does Replay ensure the extracted logic is 100% accurate?#

Replay provides a side-by-side comparison between the recorded legacy workflow and the newly generated modern component. This "Visual Testing" ensures that every button, logic branch, and data field in the new system matches the proven behavior of the legacy system.

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Conclusion: Stop Rewriting, Start Recording#

The transition to 5G is the most significant capital expenditure in the history of telecommunications. Yet, the ROI of these networks is being strangled by legacy billing systems that cannot adapt to the speed of modern software.

By focusing on telecom billing modernization extracting through Visual Reverse Engineering, carriers can bypass the 18-month "Rewrite Trap." You can preserve the complex business logic that makes your billing system work while moving to a modern, scalable, and documented React-based architecture.

Ready to modernize without rewriting? Book a pilot with Replay