SLC

Technical Architecture & Design Document

1. Overall Project Details

Project SLC is a premium, high-performance communication suite designed to provide secure, real-time connectivity across mobile platforms. It serves as a unified ecosystem for instant messaging, high-fidelity video conferencing, and "World Calls"—a specialized integration that bridges digital VOIP with traditional PSTN (Public Switched Telephone Network) lines. By leveraging a distributed serverless architecture, SLC ensures sub-100ms latency for messaging while providing enterprise-grade security and a credit-based global calling system.

2. Target Audience

The primary users of Project SLC include:

• Privacy-Conscious Individuals: Users seeking a secure, encrypted alternative to mainstream messaging apps for personal data protection.
• Global Travelers & Expats: Individuals needing a reliable, low-cost way to call international phone numbers (PSTN) directly from a mobile app.
• Small to Mid-Sized Teams: Organizations requiring a private, branded communication tool for internal chat and video coordination without the overhead of enterprise bloat.

3. User Experience & Workflow

The platform is built around a "Connectivity First" philosophy, ensuring that users can transition from a simple text chat to a high-definition video call or a global phone call with a single tap.

User Journey Flowchart

4. Technical Architecture Flow

Project SLC utilizes a Hybrid Serverless Architecture. The frontend manages the heavy lifting of media rendering and real-time state synchronization, while the backend is orchestrated through Firebase Cloud Functions and specialized communication providers.

System Architecture

5. Developer Role & Implementation Focus

The development of Project SLC focuses on extreme reliability and low-latency interaction. Core implementation areas include:

• Real-time Synchronization: Implementing Firebase RTDB for instantaneous messaging, typing indicators, and online presence.
• High-Fidelity Media: Orchestrating GetStream and Twilio SDKs to handle adaptive bitrate video and crystal-clear audio.
• Secure Billing Logic: Developing robust Firebase Cloud Functions to handle PSTN call initiation and atomic credit deductions from user accounts.
• Push Notification Pipeline: Engineering a dual-path notification system (Expo + Direct FCM) to ensure message delivery even when the app is in "Doze" mode.

6. Technology Stack & Tools Used

Frontend Environment:

• Core: React Native (v0.81), Expo (v54), TypeScript
• Styling: NativeWind (Tailwind CSS), Gluestack UI
• State: Zustand (Global State), React Query (Server State)
• Utilities: Lottie (Animations), Expo Camera, Expo Contacts

Backend Infrastructure:

• Runtime: Node.js (Firebase Cloud Functions)
• Databases: Firebase Realtime Database (Live Sync), Firestore (Profiles/History)
• Identity: Firebase Auth (OTP & Social)
• Push: Firebase Cloud Messaging (FCM), Expo Push Service

Communication & External APIs:

• Video/Voice: GetStream Video SDK, Twilio Programmable Video
• PSTN Calling: Twilio Voice SDK & TwiML
• Intelligence: Google Cloud Translation API (Real-time Chat Translation)

7. Communication Structure (RTDB & Cloud Functions)

The platform ensures a fluid experience by using Realtime Database for UI-facing events and Cloud Functions for complex backend orchestration.

PSTN Call Execution Flow