Choosing the right real-time protocol is crucial for your application’s success. This comprehensive guide helps you navigate the decision based on your specific requirements, constraints, and use cases.

Quick Decision Framework

Primary Questions

1. Do you need bidirectional communication?

   • ✅ Yes → Consider WebSockets, WebTransport, MQTT, WebRTC, gRPC
   • ❌ No → Consider SSE, HTTP streaming, Long Polling

2. Is ultra-low latency critical (less than 50ms)?

   • ✅ Yes → WebRTC, WebTransport, WebSockets
   • ❌ No → Any protocol based on other requirements

3. Do you need to work through restrictive firewalls?

   • ✅ Yes → WebSockets, SSE, Long Polling
   • ❌ No → Consider all options including WebTransport, WebRTC

4. Is browser support important?

   • ✅ Yes → WebSockets (99%+), SSE (98%+), Long Polling (100%)
   • ⚠️ Limited → WebTransport (Chrome/Edge), WebRTC (95%+)

Protocol Comparison Matrix

Protocol	Bidirectional	Latency	Complexity	Browser Support	Best For
WebSockets	✅ Yes	Low	Medium	99%+	Real-time apps, chat, gaming
SSE	❌ No	Low	Simple	98%+	News feeds, notifications
Long Polling	⚠️ Simulated	High	Simple	100%	Legacy support, simple updates
WebTransport	✅ Yes	Very Low	Complex	Limited	Next-gen apps, gaming
MQTT	✅ Yes	Low	Medium	Via bridge	IoT, messaging
WebRTC	✅ Yes	Ultra Low	Complex	95%+	Video/audio, P2P
gRPC	✅ Yes	Low	Complex	Via proxy	Microservices

Decision Tree

Start Here
    │
    ├─ Need real-time communication?
    │   │
    │   ├─ No → Use traditional HTTP REST APIs
    │   │
    │   └─ Yes → Continue
    │       │
    │       ├─ Need bidirectional data flow?
    │       │   │
    │       │   ├─ No → Use SSE or HTTP streaming
    │       │   │
    │       │   └─ Yes → Continue
    │       │       │
    │       │       ├─ Building for IoT/embedded?
    │       │       │   │
    │       │       │   └─ Yes → Use MQTT
    │       │       │
    │       │       ├─ Need peer-to-peer or media streaming?
    │       │       │   │
    │       │       │   └─ Yes → Use WebRTC
    │       │       │
    │       │       ├─ Building microservices?
    │       │       │   │
    │       │       │   └─ Yes → Consider gRPC
    │       │       │
    │       │       ├─ Need cutting-edge performance?
    │       │       │   │
    │       │       │   └─ Yes → Consider WebTransport
    │       │       │
    │       │       └─ Standard real-time web app?
    │       │           │
    │       │           └─ Use WebSockets ✓

Use Case Recommendations

Chat Applications

Recommended: WebSockets

• Bidirectional messaging
• Presence detection
• Typing indicators
• Message delivery confirmation

Alternative: Consider WebTransport for next-generation apps

Live Dashboards

Recommended: WebSockets or SSE

• WebSockets for interactive dashboards
• SSE for read-only displays
• Consider update frequency and data volume

Gaming

Recommended: WebSockets or WebTransport

• WebSockets for turn-based and casual games
• WebTransport for high-performance requirements
• WebRTC for P2P gaming

IoT Applications

Recommended: MQTT

• Designed for constrained devices
• Efficient binary protocol
• Built-in QoS levels
• Bridge to WebSockets for web clients

Video/Audio Streaming

Recommended: WebRTC

• Ultra-low latency
• P2P capabilities
• Built-in media handling
• NAT traversal

Financial Trading

Recommended: WebSockets

• Reliable bidirectional communication
• Wide infrastructure support
• Can be secured with TLS
• Proven at scale

Implementation Complexity

Simple to Implement

1. Long Polling - Basic HTTP knowledge sufficient
2. SSE - Simple server push, minimal client code
3. WebSockets (with libraries) - Well-documented, many tools

Medium Complexity

4. WebSockets (raw) - Connection management, reconnection logic
5. MQTT - Broker setup, topic design
6. gRPC-Web - Protocol buffers, code generation

Complex Implementation

7. WebTransport - Limited documentation, evolving spec
8. WebRTC - Signaling servers, ICE/STUN/TURN setup

Infrastructure Considerations

WebSockets

• Most CDNs and proxies support WebSockets
• Load balancing requires sticky sessions
• Horizontal scaling needs careful planning

SSE

• Works through most proxies
• Simple to cache and scale
• No special infrastructure requirements

WebTransport

• Requires HTTP/3 support
• Limited CDN support currently
• Firewall traversal can be challenging

MQTT

• Requires MQTT broker deployment
• Many cloud-hosted options available
• Bridge needed for web clients

Security Considerations

All protocols can be secured:

• WebSockets: Use WSS (WebSocket Secure)
• SSE: Use HTTPS
• WebTransport: Built on QUIC (always encrypted)
• MQTT: Use TLS, authentication options
• WebRTC: Mandatory encryption
• gRPC: TLS support built-in

Making Your Decision

Choose WebSockets when:

• You need bidirectional real-time communication
• Browser compatibility is crucial (99%+ support)
• You want proven, stable technology
• Your team has JavaScript/web expertise
• You need extensive library ecosystem

Consider alternatives when:

• SSE: Unidirectional updates are sufficient
• WebTransport: You need cutting-edge performance
• MQTT: Building IoT or message-centric systems
• WebRTC: Media streaming or P2P is required
• gRPC: Building microservice architectures

Implementation Resources

Getting Started with WebSockets

• Use established libraries (Socket.IO, Ably, Pusher)
• Implement reconnection logic
• Handle connection state properly
• Plan for horizontal scaling

Testing Your Choice

1. Prototype with your specific use case
2. Test under realistic network conditions
3. Measure latency and throughput
4. Evaluate operational complexity
5. Consider long-term maintenance

Conclusion

WebSockets remain the most versatile and widely-supported option for real-time web applications. They offer the best balance of:

• Broad compatibility (99%+ browsers)
• Proven reliability at scale
• Extensive tooling and libraries
• Reasonable complexity
• Strong community support

However, specific use cases may benefit from alternatives:

• Choose SSE for simple server-to-client streaming
• Choose WebRTC for media or P2P requirements
• Choose MQTT for IoT deployments
• Consider WebTransport for future-proof applications

The key is matching the protocol to your specific requirements rather than choosing based on novelty or theoretical performance alone.

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Written by Matthew O’Riordan, technical co-founder of Ably with 25+ years of experience building real-time systems powering billions of devices worldwide.