https://alamrafiul.com/tags/unreliable-communication/ Recent content in Unreliable-Communication on Rafiul Alam https://alamrafiul.com/papermod-cover.png https://alamrafiul.com/papermod-cover.png Hugo -- gohugo.io en Tue, 14 Oct 2025 00:00:00 +0000 https://alamrafiul.com/blogs/two-generals-problem/ Tue, 14 Oct 2025 00:00:00 +0000 https://alamrafiul.com/blogs/two-generals-problem/ <h2 id="the-two-generals-problem">The Two Generals&rsquo; Problem</h2> <p>The Two Generals&rsquo; Problem, also known as the Two Armies Problem, is a classic thought experiment that demonstrates the <strong>impossibility</strong> of achieving perfect consensus over an unreliable communication channel. It was first formulated by E. A. Akkoyunlu, K. Ekanadham, and R. V. Huber in 1975.</p> <h2 id="the-scenario">The Scenario</h2> <p><strong>Two armies need to coordinate an attack:</strong></p> <ul> <li>General A and General B surround an enemy</li> <li>They must attack <strong>simultaneously</strong> to win</li> <li>If only one attacks → defeat</li> <li>They communicate via <strong>messengers</strong> through enemy territory</li> <li>Messages can be <strong>lost</strong> or <strong>intercepted</strong></li> <li><strong>Question</strong>: Can they guarantee coordinated attack?</li> </ul> <h2 id="the-impossible-dilemma">The Impossible Dilemma</h2> <div class="mermaid">%%{init: {'theme':'dark', 'themeVariables': {'primaryTextColor':'#e5e7eb','secondaryTextColor':'#e5e7eb','tertiaryTextColor':'#e5e7eb','textColor':'#e5e7eb','nodeTextColor':'#e5e7eb','edgeLabelText':'#e5e7eb','clusterTextColor':'#e5e7eb','actorTextColor':'#e5e7eb'}}}%% sequenceDiagram participant GA as General A participant Enemy as Enemy Territory participant GB as General B Note over GA: Wants to attack<br/>at dawn GA->>Enemy: "Attack at dawn" Enemy->>GB: Message delivered Note over GB: Received message,<br/>but A doesn't know! GB->>Enemy: "Acknowledged" Enemy->>GA: ACK delivered? Note over GA: Received ACK,<br/>but B doesn't know! GA->>Enemy: "ACK of ACK" Enemy->>GB: Delivered? Note over GA,GB: This never ends! </div> <h2 id="the-core-problem">The Core Problem</h2> <p><strong>The infinite regress:</strong></p>