Cross-Platform Multiplayer Networking in Unity: FishNet, Mirror, and Photon Compared

The Three Contenders

FishNet - An open-source networking framework built specifically for Unity. Created by FirstGearGames, it positions itself as a modern, performance-focused alternative to Mirror.

Mirror - An open-source successor to Unity's deprecated UNET. The most widely adopted Unity networking solution, with a large community and extensive documentation.

Photon (PUN / Fusion) - A commercial networking platform with both client-hosted (PUN) and server-authoritative (Fusion) options. Provides managed infrastructure so you do not run your own servers.

Architecture: Server-Authoritative vs Peer-to-Peer

This is the most fundamental decision, and it constrains your framework choice.

Server-Authoritative - The server is the single source of truth. Clients send inputs; the server validates them and broadcasts the result. Cheating is significantly harder because the client cannot unilaterally modify game state.

When you need it: Any game with competitive mechanics, real-money economies, leaderboards, or persistent worlds. For Domi Online, server authority was non-negotiable as the game has a player-driven economy where item duplication or stat manipulation would destroy the game.

Frameworks: FishNet (excellent), Mirror (good), Photon Fusion (good, managed)

Peer-to-Peer / Client-Hosted - One player acts as the host. Other players connect to them. Simpler to set up, but the host has an inherent latency advantage and can potentially cheat.

When it works: Co-op games, casual multiplayer, games where cheating has low impact.

Frameworks: Mirror (common use case), Photon PUN (designed for this), FishNet (supports it but overkill)

Key Takeaway: Choose your architecture first, then pick the framework that best supports it. Do not let framework familiarity drive an architectural decision.

FishNet: Our Framework of Choice for Domi Online

Why We Chose It

When we evaluated networking options for Domi Online, we needed:

• Server-authoritative architecture with full state control
• Efficient bandwidth usage (MMORPG with hundreds of concurrent players)
• Extensibility for custom serialisation of our 64-bit progression system
• Active development and responsive maintainer

FishNet met all four criteria.

Strengths

• Prediction and reconciliation - FishNet's client-side prediction is mature and well-documented. Players see immediate feedback on their actions while the server validates asynchronously.
• Object spawning - network object lifecycle management is clean. Spawning, despawning, and ownership transfer are straightforward.
• Custom serialisers - we wrote custom serialisation for our 64-bit stat system. FishNet's serialiser API made this painless.
• Performance - benchmarks consistently show lower bandwidth overhead than Mirror for equivalent workloads.
• Active development - the maintainer ships regular updates and is responsive to issues.

Weaknesses

• Smaller community - fewer tutorials, Stack Overflow answers, and third-party integrations compared to Mirror
• Documentation gaps - improving rapidly, but some advanced features require reading source code
• Learning curve - developers coming from PUN or Mirror will need adjustment time

Mirror: The Community Standard

Strengths

• Massive community - the most widely used Unity networking solution. Finding answers to common problems is easy.
• Extensive transports - supports WebSocket, KCP, Steam, and more out of the box
• Battle-tested - used in hundreds of shipped games across diverse genres
• Low barrier to entry - getting a basic multiplayer prototype running is fast
• Well-documented - comprehensive documentation and numerous tutorials

Weaknesses

• Bandwidth efficiency - Mirror's default serialisation is less efficient than FishNet's. For small-scale multiplayer (4-16 players) this is irrelevant. For MMO-scale, it adds up.
• Prediction - client-side prediction exists but is less mature than FishNet's implementation. Requires more manual work for smooth results.
• Host migration - limited support. If the host disconnects in a client-hosted game, recovery is complex.

When to Choose Mirror

Mirror is the right choice when:

• Your game has 2-16 players (co-op, competitive matches)
• Development speed matters more than bandwidth optimisation
• Your team has existing Mirror experience
• You need maximum community support and third-party asset compatibility

Photon: Managed Infrastructure

Strengths

• No server management - Photon handles matchmaking, relay servers, and infrastructure scaling. You do not run your own servers.
• Global infrastructure - data centres worldwide with automatic region selection
• Quick prototyping - PUN (Photon Unity Networking) gets a multiplayer prototype running in hours
• Photon Fusion - their newer framework supports server-authoritative architecture with tick-based simulation, comparable to FishNet in capability

Weaknesses

• Cost at scale - Photon charges per CCU (concurrent user). For an MMORPG with thousands of concurrent players, costs escalate quickly. This was a decisive factor in our decision not to use Photon for Domi Online.
• Vendor lock-in - your networking code is tied to Photon's API. Migrating away is a significant rewrite.
• Less control - you cannot inspect or modify the server infrastructure. Debugging latency issues requires Photon's support team.
• PUN limitations - PUN is client-hosted only. For server-authoritative, you need Fusion, which has a steeper learning curve.

When to Choose Photon

Photon is the right choice when:

• You do not want to manage servers
• Your CCU will stay under a few hundred (where the free/affordable tiers apply)
• You need rapid prototyping with minimal backend work
• Global matchmaking is a requirement and you want it out of the box

Head-to-Head Comparison

Framework Comparison at a Glance

Here is how FishNet, Mirror, and Photon compare across the factors that matter most when choosing a multiplayer framework:

Our Recommendation

There is no universal "best" framework. The right choice depends on your game:

• Building an MMO or competitive game with a persistent world? FishNet. The bandwidth efficiency and prediction systems justify the smaller community. This is what we chose for Domi Online.
• Building a co-op or small-scale multiplayer game? Mirror. The community support and rapid development speed outweigh its efficiency gap at small player counts.
• Building a prototype or MVP with no backend team? Photon PUN. Get something playable fast and evaluate whether the pricing model works at your projected scale.
• Need server-authoritative without managing infrastructure? Photon Fusion. But model your CCU costs carefully before committing.

Key Takeaway: The framework you prototype with is not necessarily the framework you ship with. Evaluate based on your production requirements, not your prototyping requirements.

Related Reading

• Domi Online Case Study - Our MMORPG networking architecture in practice
• Network Engineering Services - How we approach multiplayer projects
• Domi Online Project Page - The game itself
• Game Development Cost Estimator - Multiplayer significantly affects project cost.