All real-time multiplayer games—from shooters to MOBAs—depend on one core mechanism:
the game loop, also known as the simulation loop.

The game loop is the server’s “heartbeat.”
It controls how often:

• Player inputs are processed
• The world updates
• Physics and collisions resolve
• Timers and cooldowns advance
• NPCs and AI behave
• State is broadcast to players

Understanding the game loop is essential for building fair, predictable, real-time gameplay.

1. What Is a Game Loop?

A game loop is a repeating cycle that advances the simulation one step at a time.

A modern online game backend is not a single monolithic server.
It is a collection of specialized services working together to deliver real-time gameplay, persistent worlds, and social systems.

This chapter introduces the core architectural building blocks:

• Gateway / Connection Layer
• Room / Match Server
• World Server
• Matchmaking Service
• Persistence Layer (DB, Cache)
• Supporting Services (Chat, Social, Inventory, etc.)

By the end, you’ll understand how these pieces fit together into a working online game.

Networking is the communication layer between player clients and the game server.
It is the foundation that defines how fast, how reliable, and how scalable your online game can be.

This chapter introduces the most widely used networking models in modern game development:

• TCP
• UDP
• WebSocket
• gRPC
• Custom binary protocols

Along the way, we discuss latency, reliability, packet handling, and real-world usage patterns.

1. Why Networking Matters in Multiplayer Games

Every time a player moves, shoots, crafts, chats, or interacts with the world, the client and server must exchange data.

Online multiplayer games—from small casual titles to massive MMOs—are powered by one critical element:
the game server.

This chapter gives a clear, friendly, and complete introduction to what game servers are, why they exist, how they work, and what technologies surround them.
It is written for total beginners, but structured with the accuracy expected of modern production systems.

1. What Is an Online Game Server?

A game server is a backend program running on a remote machine.
It manages all shared rules, simulation, and persistence in a multiplayer game.

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