Why multiplayer requires networking in Unity - Why It Works This Way

Overview - Why multiplayer requires networking

What is it?

Multiplayer games let many players play together at the same time. To do this, the game needs a way to share information between all players' devices. Networking is the system that connects these devices so they can send and receive game data in real time.

Why it matters

Without networking, players would only be able to play alone or pass the device around. Networking makes it possible to play with friends or strangers anywhere in the world, creating fun and social experiences. It solves the problem of keeping all players' games in sync so everyone sees the same game world.

Where it fits

Before learning this, you should understand basic game development and how games run on a single device. After this, you can learn about specific networking tools and techniques in Unity, like client-server models and synchronization methods.

Mental Model

Core Idea

Networking connects multiple players' devices so they can share game information instantly and play together as one game.

Think of it like...

It's like a group of friends playing a board game in different rooms but using walkie-talkies to tell each other their moves so everyone knows what is happening.

┌───────────────┐       ┌───────────────┐       ┌───────────────┐
│ Player 1 Dev  │──────▶│   Network     │──────▶│ Player 2 Dev  │
│ (Sends input) │       │ (Shares data) │       │ (Receives)    │
└───────────────┘       └───────────────┘       └───────────────┘
         ▲                                              │
         │                                              ▼
┌───────────────┐                               ┌───────────────┐
│ Player 3 Dev  │◀──────────────────────────────│ Player 4 Dev  │
│ (Receives)   │                               │ (Sends input) │
└───────────────┘                               └───────────────┘

Build-Up - 6 Steps

1

Foundation

What is multiplayer gaming

Concept: Understanding the basic idea of multiplayer games where multiple people play together.

Multiplayer games allow two or more players to play the same game at the same time. This can be on the same device or on different devices. The goal is to share the game experience.

Result

You know that multiplayer means playing together, not alone.

Understanding what multiplayer means sets the stage for why devices need to communicate.

2

Foundation

Why devices need to communicate

Concept: Introducing the need for devices to share information to keep the game in sync.

When players play on different devices, each device has its own copy of the game. To make sure everyone sees the same game world, devices must send updates about player actions and game changes to each other.

Result

You realize that without communication, each player would see a different game.

Knowing that devices must share data explains why networking is necessary.

3

Intermediate

What networking means in games

🤔Before reading on: do you think networking means just connecting devices or also managing game data? Commit to your answer.

Concept: Networking is not just connection but also managing how game data moves between players.

Networking in games means creating a system that connects players' devices and controls how game information like player moves, scores, and game events are sent and received quickly and reliably.

Result

You understand networking as both connection and data sharing.

Understanding networking as data management helps grasp why it can be complex and needs special tools.

4

Intermediate

How networking keeps games in sync

🤔Before reading on: do you think all players' devices update at the same time or with delays? Commit to your answer.

Concept: Networking synchronizes game states so all players see the same game world despite delays.

Networking sends updates about player actions and game changes to all devices. It handles delays and differences in timing so that the game feels smooth and fair for everyone.

Result

You see how networking solves the problem of keeping all players' games aligned.

Knowing synchronization challenges explains why networking code must handle timing and delays carefully.

5

Advanced

Client-server model in multiplayer

🤔Before reading on: do you think all players talk directly to each other or through a central system? Commit to your answer.

Concept: Most multiplayer games use a client-server model where a central server manages the game state.

In the client-server model, each player’s device (client) sends input to a central server. The server processes the game logic and sends updates back to all clients. This keeps the game fair and consistent.

Result

You understand the common architecture behind multiplayer networking.

Knowing the client-server model helps you design multiplayer games that scale and stay secure.

6

Expert

Challenges of networking in real games

🤔Before reading on: do you think networking is mostly about sending data or also about handling errors and cheating? Commit to your answer.

Concept: Networking must handle errors, delays, cheating, and performance to create a good multiplayer experience.

Real multiplayer games face problems like lost data packets, slow connections, players trying to cheat, and keeping the game fast. Networking code includes ways to detect and fix these issues, like prediction, lag compensation, and security checks.

Result

You see that networking is complex and requires careful design beyond just sending messages.

Understanding these challenges prepares you to build robust multiplayer systems.

Under the Hood

Networking works by opening communication channels between devices using protocols like TCP or UDP. Data packets containing game information are sent over the internet or local networks. The game engine processes incoming packets to update the game state and sends outgoing packets to inform other players. Techniques like interpolation and prediction smooth out delays and packet loss.

Why designed this way?

Networking was designed to solve the problem of sharing real-time data between separate devices reliably and efficiently. Early games used direct connections, but this was unreliable and insecure. The client-server model and protocols like UDP were chosen to balance speed and reliability, allowing fast-paced games to run smoothly.

┌───────────────┐       ┌───────────────┐       ┌───────────────┐
│ Player Client │──────▶│   Game Server │──────▶│ Player Client │
│ (Sends input) │       │ (Processes)   │       │ (Receives)    │
└───────────────┘       └───────────────┘       └───────────────┘
         ▲                                              │
         │                                              ▼
┌───────────────┐                               ┌───────────────┐
│ Player Client │◀──────────────────────────────│ Player Client │
│ (Receives)   │                               │ (Sends input) │
└───────────────┘                               └───────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Do you think multiplayer games can work perfectly without any network delays? Commit to yes or no.

Common Belief: Multiplayer games always run perfectly with no delays or lag.

Reality: Network delays and lag are normal and unavoidable; games use techniques to hide or reduce their impact.

Why it matters: Expecting perfect real-time play without delays leads to frustration and poor design choices.

Quick: Do you think all multiplayer games connect players directly without a server? Commit to yes or no.

Common Belief: All multiplayer games connect players directly to each other (peer-to-peer).

Reality: Most multiplayer games use a central server to manage the game state for fairness and security.

Why it matters: Assuming peer-to-peer can cause security risks and synchronization problems in real games.

Quick: Do you think networking only sends player inputs and nothing else? Commit to yes or no.

Common Belief: Networking only sends player inputs; the rest happens locally on each device.

Reality: Networking sends many types of data including game state updates, events, and synchronization info.

Why it matters: Ignoring other data types can cause inconsistent game states and bugs.

Quick: Do you think networking code is simple and the same for all games? Commit to yes or no.

Common Belief: Networking code is simple and works the same way for every multiplayer game.

Reality: Networking is complex and must be tailored to each game's needs, handling errors, cheating, and performance.

Why it matters: Underestimating complexity leads to buggy or insecure multiplayer experiences.

Expert Zone

1

Latency compensation techniques like client-side prediction are essential to hide delays but can cause visual glitches if not tuned well.

2

Authoritative servers prevent cheating by controlling the true game state, but increase server load and complexity.

3

Choosing between TCP and UDP protocols affects reliability and speed; many games use UDP with custom reliability layers.

When NOT to use

Networking is not needed for single-player games or local multiplayer on the same device. For local multiplayer on one machine, direct input sharing without networking is simpler and faster.

Production Patterns

Real-world multiplayer games use client-server architecture with authoritative servers, implement lag compensation, and use matchmaking services. They also monitor network quality and adjust game behavior dynamically to maintain smooth play.

Connections

Distributed Systems

Networking in multiplayer games is a specialized form of distributed systems where multiple computers coordinate state.

Understanding distributed systems principles like consensus and fault tolerance helps design robust multiplayer networking.

Real-time Communication Protocols

Multiplayer networking relies on protocols like UDP and TCP for fast and reliable data transfer.

Knowing how these protocols work explains why some data is lost and how games handle it.

Social Psychology

Multiplayer games create social experiences that depend on real-time interaction and communication.

Understanding human social behavior helps design networking features that improve player cooperation and enjoyment.

Common Pitfalls

#1 Assuming all players have perfect internet connections.

Wrong approach:

Sending large amounts of data every frame without compression or optimization.

Correct approach:

Sending only necessary data, compressing it, and using techniques like interpolation to handle delays.

Root cause:

Not considering network limitations and variability in player connections.

#2 Trusting client devices to control game state.

Wrong approach:

Allowing clients to decide game outcomes without server verification.

Correct approach:

Using an authoritative server to validate all important game actions.

Root cause:

Misunderstanding security risks and cheating possibilities in multiplayer games.

#3 Ignoring synchronization of game state across players.

Wrong approach:

Updating only local player data and not sending updates to others.

Correct approach:

Broadcasting state changes to all players to keep the game consistent.

Root cause:

Not realizing that each device runs its own copy of the game.

Key Takeaways

Multiplayer games require networking to connect players' devices and share game information in real time.

Networking manages both the connection and the flow of game data to keep all players' views synchronized.

The client-server model is the most common architecture to ensure fairness, security, and consistency.

Networking must handle challenges like delays, lost data, cheating, and varying connection quality.

Understanding networking deeply helps build multiplayer games that are fun, fair, and reliable.