When Digital Voice Dies: Navigating the UK PSTN Switch-Off & Mobile Mast Battery Collapse

# OFF-GRID ACADEMY FIELD MANUAL 04 ## When Digital Voice Dies: Navigating the UK PSTN Switch-Off & Mobile Mast Collapse ### 1. The Hidden Fragility of Full Fibre (FTTP) For 100 years, UK copper landlines (PSTN) were powered by **-48V DC battery rooms and diesel generators** inside hardened BT exchanges. When your house lost mains electricity, your corded telephone still rang and dialled 999. By 2027, the UK PSTN switch-off migrates every premises to **Digital Voice (VoIP over FTTP)**. Your landline now plugs into the back of a domestic broadband router, which connects to an optical network terminal (ONT) on the wall—**both of which die at Second 0 of a power cut**. ### 2. The 3-Tier Telecom Failure Cascade 1. **Minute 0 (Home ONT & Router Death):** Unless backed by a 12V DC UPS, your home broadband and VoIP phone disconnect immediately. 2. **Minute 5 (Cellular Signalling Storm):** Millions of citizens simultaneously drop off Wi-Fi onto 4G/5G macro-cells, saturating random-access channels (RACH). Data throughput collapses. 3. **Hour 1 to Hour 4 (Mast Battery Exhaustion):** Standard UK cell sites exhaust their lead-acid/lithium backup cabinets. The tower powers down completely. ### 3. The EOD PACE Architecture - **P — Primary:** FTTP + 5G with a **12V DC inline Mini-UPS** powering the Openreach ONT and router for up to 8 hours (covers local feeder trips while the main exchange still has power). - **A — Alternate:** **Starlink Mini powered via 12V/24V-to-48V DC step-up converter** (`EOD-ENT-022`), bypassing terrestrial exchanges entirely. - **C — Contingency:** **868MHz LoRa Meshtastic Mesh** (`EOD-RF-001` / `002`) for text & GPS coordination across 5–30km. - **E — Emergency:** **VHF/UHF Simplex & PMR446 Voice** (`EOD-RF-003`) on pre-agreed family/site channels at top-of-the-hour schedules.