Choosing the right architecture

Introduction

Selecting the right WebRTC architecture is a critical decision that impacts performance, scalability, cost, and user experience. Throughout this module, we've explored various architectures—P2P, MCU, SFU, Simulcast, and SFU Cascading—each with its unique strengths and trade-offs. There's no universal solution; the optimal choice depends on your specific requirements, constraints, and goals.

This lesson synthesizes the key insights from previous lessons to help you make an informed decision. We'll examine each architecture through the lens of real-world considerations, helping you understand which approach best suits your use case.

SFU with Cascading: Best Option for Most Use Cases

Why It's the Industry Standard

SFU with cascading has emerged as the dominant architecture for modern video platforms, and for good reason. It combines the efficiency of selective forwarding with the global scale of distributed systems, creating a solution that excels across multiple dimensions.

Most major video platforms have adopted variations of this architecture. Stream also uses SFU Cascading to allow the best possible experience for users around the world.

Key Advantages

The architecture provides several critical benefits:

1. Scalability at Global Scale: By distributing load across multiple regional SFUs, the system can handle millions of concurrent users. Each SFU serves its local region efficiently while seamlessly connecting to the global network.

2. Optimal Latency Management: Participants connect to nearby SFUs, minimizing network distance. Inter-SFU connections use optimized routes, resulting in the lowest possible end-to-end latency for global calls.

3. Built-in Redundancy: Multiple SFUs eliminate single points of failure. If one server fails, participants can be seamlessly migrated to others without dropping calls.

4. Quality of Experience (QoE) Optimization: The system can dynamically adjust routing, quality levels, and server assignments to maintain optimal experience for all participants.

Implementation Considerations

While SFU cascading offers the best overall solution, it comes with significant implementation complexity:

            // Example of the complexity involved in SFU cascading
class CascadedSFUManager {
  constructor() {
    this.regions = new Map();
    this.routingTable = new GlobalRoutingTable();
    this.stateManager = new DistributedStateManager();
  }

  async handleGlobalCall(participants) {
    // Complex logic for global participant management
    const regionalAssignments = await this.assignToRegions(participants);
    const interRegionalRoutes = await this.calculateOptimalRoutes(regionalAssignments);
    await this.establishCascadedConnections(interRegionalRoutes);
  }
}
        

When to Choose SFU Cascading

Select this architecture when:

• Building a platform for global audiences
• Requiring enterprise-grade reliability
• Needing to scale beyond thousands of participants
• Prioritizing user experience over infrastructure costs
• Having the resources to manage complex systems or budget for managed services

Peer-to-Peer (P2P): Most Cost-Effective

Understanding the Economics

P2P architecture eliminates server costs for media relay, making it the most economical option for certain use cases. Since participants connect directly, the only infrastructure required is for signaling and coordination.

Cost-Benefit Analysis

The true cost picture includes several factors:

1. Infrastructure Costs: Minimal server requirements—only signaling servers needed
2. Bandwidth Costs: Distributed to end users rather than centralized
3. Development Costs: Higher due to complexity of NAT traversal and connection management
4. Maintenance Costs: Ongoing challenges with diverse network conditions

Technical Limitations

P2P faces inherent scaling challenges:

            // P2P connection complexity grows quadratically
function calculateP2PConnections(participants) {
  return (participants * (participants - 1)) / 2;
}

// Example: 5 participants = 10 connections
// Example: 10 participants = 45 connections
        

Each participant must:

• Encode their stream once for each other participant
• Maintain multiple concurrent connections
• Handle increased CPU and bandwidth load

When to Choose P2P

Ideal for scenarios where:

• Cost minimization is the primary concern
• Calls involve 2-4 participants maximum
• Users have reliable, high-bandwidth connections
• Geographic proximity between participants
• Privacy is paramount (true end-to-end encryption possible)

MCU: Better for Legacy Systems

Historical Context

MCU architecture was developed when client devices had limited processing power and bandwidth. It centralizes all processing on powerful servers, allowing even basic devices to participate in multi-party calls.

Modern Relevance

While largely superseded by SFU architectures, MCUs still serve important niches:

1. Legacy System Integration: Many enterprise systems still use MCU-based protocols
2. Specialized Use Cases: Broadcasting, recording, and transcoding scenarios
3. Device Compatibility: Supporting very old or limited devices
4. Compliance Requirements: Some industries require server-side processing

Architectural Trade-offs

MCUs involve significant trade-offs:

            // MCU processing requirements scale linearly with participants
class MCUServer {
  calculateResourceRequirements(participants, quality) {
    return {
      cpu: participants * this.cpuPerStream * quality.factor,
      memory: participants * this.memoryPerStream,
      bandwidth: participants * quality.bitrate,
      transcoding: participants * this.transcodingCost
    };
  }
}
        

The server must:

• Decode all incoming streams
• Mix audio and compose video
• Re-encode for each participant
• Handle all processing centrally

When to Choose MCU

Consider MCU when:

• Integrating with legacy systems that require it
• Supporting devices with minimal processing power
• Server-side recording or processing is mandatory
• Budget allows for expensive server infrastructure
• End-to-end encryption is not required

SFU without Cascading: Good for Simple Use Cases

Simplified Architecture

A single SFU provides many benefits of selective forwarding without the complexity of cascading. This makes it an attractive option for organizations that want to self-host their infrastructure.

Practical Limitations

Single SFU deployments face several constraints:

1. Geographic Limitations: Higher latency for distant participants
2. Scaling Ceiling: Limited by single server capacity
3. Single Point of Failure: No built-in redundancy
4. Resource Constraints: All traffic flows through one location

Implementation Simplicity

The reduced complexity makes self-hosting feasible:

            // Simple SFU implementation
class BasicSFU {
  constructor() {
    this.participants = new Map();
    this.streams = new Map();
  }

  async handleParticipant(participant) {
    // Straightforward connection handling
    this.participants.set(participant.id, participant);
    await this.setupStreamForwarding(participant);
  }
}
        

When to Choose Single SFU

Appropriate for:

• Regional applications with local user base
• Medium-scale deployments (up to few hundred participants)
• Organizations wanting to self-host
• Projects with limited development resources
• Use cases where some latency is acceptable

Decision Framework

Step 1: Define Requirements

Start by clearly identifying your needs:

• Expected number of participants per call
• Geographic distribution of users
• Quality and latency requirements
• Budget constraints
• Development resources
• Compliance and security needs

Step 2: Evaluate Constraints

Consider your limitations:

• Infrastructure budget
• Development expertise
• Operational capabilities
• Time to market
• Scalability requirements

Step 3: Match Architecture to Needs

*For small groups only

Step 4: Consider Hybrid Approaches

Many successful platforms use hybrid architectures:

• P2P for 1:1 calls, SFU for group calls
• MCU for recording, SFU for live participants
• Regional SFUs with selective cascading

Implementation Recommendations

For Startups and Small Teams

1. Start Simple: Begin with P2P for 1:1 calls and basic SFU for small groups
2. Use Managed Services: Leverage providers like Stream or Agora for complex architectures
3. Plan for Growth: Design with future scaling in mind
4. Monitor and Iterate: Collect metrics to inform architectural decisions

For Enterprise Applications

1. Prioritize Reliability: Choose SFU cascading for global reach and redundancy
2. Consider Compliance: Evaluate MCU if server-side processing is required
3. Invest in Monitoring: Implement comprehensive observability
4. Plan for Integration: Ensure compatibility with existing systems

For Specialized Use Cases

1. Education Platforms: SFU with simulcast for varied device capabilities
2. Telehealth: P2P for privacy, with fallback to SFU
3. Gaming: Custom hybrid architectures optimized for low latency
4. Broadcasting: MCU for production, SFU for distribution

Conclusion

Choosing the right WebRTC architecture requires careful consideration of multiple factors. While SFU with cascading offers the best overall solution for most modern applications, each architecture has its place:

• SFU Cascading: Best for global scale and reliability
• P2P: Optimal for cost-sensitive, small-scale applications
• MCU: Necessary for legacy integration and specialized processing
• Single SFU: Good balance for regional or medium-scale deployments

The key is to match your architecture to your specific needs, constraints, and growth plans. Start with the simplest solution that meets your requirements, but design with scalability in mind. As your application grows, you can evolve your architecture to meet changing demands.

Remember that these architectures aren't mutually exclusive. Many successful platforms use hybrid approaches, combining the strengths of different architectures to create optimal solutions for their specific use cases.