Netcode is arguably one of the most critical components of any multiplayer.

Previously, we’ve covered the insights applicable to all multiplayer game developers of Call of Duty’s skill-based matchmaking in-depth white paper.

In this article, we’ll cover the key insights that are applicable to all multiplayer game developers regarding one of the most popular online game in the world, Call of Duty, and its netcode. These insights stem from Activision’s own explainer from 2019, from Paul Hale, then Production Director at Infinity Ward, and Mitch Sanborn, then Director of Online Engineering.

The Foundation: Understanding Client-Server Architecture

Modern Warfare operates on a client-server model where multiple clients interact with a central, authoritative server. Each player's device functions as a client, constantly sending input data to the server while receiving world state updates in return. The server maintains ultimate authority over game state, processing all player inputs and broadcasting results back to every connected client.

This authoritative approach ensures consistency across all players. When you fire a weapon or move your character, both your client and the server process this input simultaneously. However, only the server's version becomes the official game state that all other players see.

What is Netcode for Online Games?

Netcode encompasses all networking systems that synchronize game states between multiple players in real-time multiplayer experiences. It handles data transmission, prediction algorithms, lag compensation, and conflict resolution when different clients report conflicting information.

Modern netcode extends far beyond simple data exchange. It includes sophisticated prediction systems, rollback mechanisms, and dynamic adaptation strategies that maintain playable experiences despite network imperfections. The term originally described the networking code within game engines but now represents the entire ecosystem of technologies enabling online multiplayer gaming.

Effective netcode must balance multiple competing priorities: responsiveness, consistency, fairness, and scalability.

What Does Netcode Do?

Netcode performs several critical functions that enable multiplayer gaming. It synchronizes player positions, actions, and game state changes across all connected clients while maintaining consistency despite network delays and data loss.

The system predicts future game states based on current trends, allowing games to continue running smoothly even when data packets arrive late or out of order. When predictions prove incorrect, rollback mechanisms rewind game state to the point of divergence and replay events with correct information.

Netcode also implements lag compensation techniques that account for network delays when determining hit registration and player interactions. These systems ensure that players with different connection qualities can compete fairly without significant disadvantages.

Additionally, modern netcode includes cheat detection and validation systems that verify client data against server expectations. This prevents malicious players from manipulating their local game state to gain unfair advantages.

When Networks Fail: The Challenge of Packet Loss

Network disruptions manifest in two primary ways. The first occurs when clients fail to receive server data, leaving players without crucial world state information. Without this data stream, client games literally don't know what to render next.

The second scenario involves the server missing client input data. Traditional approaches simply froze the affected player until data arrived, then teleported them to their new position instantly. This created jarring visual artifacts that made games unplayable.

Wireless interference, ISP traffic shaping, CPU spikes, and router buffering all contribute to packet delivery variance. These factors create unpredictable delays in the time required for data to travel between clients and servers.

Three-Pronged Solution Strategy

Infinity Ward employs three distinct strategies depending on network conditions.

• Buffering analyzes packet delivery rates in real-time, positioning clients as close as possible to the server's latest data without risking visual hitches. The system dynamically throttles client update rates up or down to maintain this precise balance.

• Extrapolation takes the last received input and assumes the player continues the same action until new data arrives. This works well for consistent movement but can cause visual "popping" when players change direction suddenly.

• Prediction treats extrapolated input as authoritative server data, creating smooth movement for all players. However, too much prediction makes the game unplayable for clients experiencing network issues.

Modern Warfare's engine supports all three approaches simultaneously, mixing strategies based on real-time network analysis for each individual client. This prevents single players with poor connections from degrading entire matches.

The "Dying Behind Cover" Phenomenon Explained

The classic frustration of dying after reaching cover illustrates netcode principles in action. When you're exposed and see a sniper's glint, your decision to run creates a complex chain of network events.

Your exposed position travels to the server, which updates your location and broadcasts it to other players. The sniper sees you in the open and fires, sending that action back to the server for authoritative processing. The server then sends the kill result back to you.

Total system latency determines how far behind cover you'll appear to die. Extrapolation can actually reduce this effect by predicting player positions ahead of actual data, effectively beating round-trip packet times when predictions prove accurate.

Data-Driven Optimization

Infinity Ward's approach extends beyond initial development into ongoing optimization based on real-world data collection. The team continuously monitors server and client behavior, gathering telemetry from individual player experiences to identify improvement opportunities.

Beta testing data confirmed their buffering approach's effectiveness, with the system consistently operating at optimal thresholds without frequent overstepping. This data-driven methodology continues post-launch through regular testing with live player populations.

Conclusion

Call of Duty Modern Warfare's netcode represents an interesting insights on the technical constraints while maintaining playable experiences for millions of global players. The system's sophisticated approach to buffering, prediction, and dynamic strategy mixing demonstrates how modern multiplayer games handle the inherent challenges of real-time networking.

The insights from Infinity Ward's engineering team reveal that great netcode isn't about eliminating network problems but rather about gracefully handling them when they inevitably occur.

Their approach of starting with solid low-latency foundations and building robust tolerance systems on top provides a blueprint for maintaining quality in even the most demanding multiplayer environments. Such Netcode was custom built, making it unavailable to most developers.

Fortunately, Edgegap’s matchmaker is the sole widely available matchmaker with integrated latency rules. As it’s fully integrated in Edgegap’s orchestrator, it also taps in the world’s largest edge network – which allows your multiplayer to deploy its game server nearest users. Reducing latency by 58% on average and delivers sub-50ms latency to 78% of your playerbase.

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This article is based on and cites the original article by Activision on their official explainer. All rights in the original content are owned by their respective owners.