Troubleshooting Common Foo DSP SSRC Issues and Fixes

Foo DSP SSRC — Best Practices and Implementation Tips

What SSRC is (brief)

SSRC (synchronization source) is an identifier used in RTP-based media streams to label the source of a stream. In DSP systems like Foo DSP, SSRCs let receivers distinguish and synchronize multiple concurrent audio/video sources, detect stream restarts, and correlate RTP packets with internal processing paths.

Best practices

• Use stable, unique SSRCs per logical source: Generate SSRCs using a high-quality RNG and ensure each logical media source (microphone, encoder instance, mixed output) has its own SSRC to avoid collisions and ambiguous stream attribution.
• Persist across short interruptions: When a stream briefly pauses (e.g., network hiccup), retain the same SSRC if the source remains the same so receivers treat it as the same source and maintain continuity.
• Change SSRC on source reset or reinitialization: If the encoder or capture pipeline is restarted or its identity changes, pick a new SSRC and signal the change via appropriate RTP/RTCP semantics (e.g., RTP sequence number reset, RTCP BYE/SSRC collision handling) so receivers can re-sync.
• Coordinate SSRCs with SSRC multiplexing (SIM) and RTX: If Foo DSP uses SSRC multiplexing or retransmission streams (RTX), reserve distinct SSRCs for primary, RTX, and FEC streams and document mappings in session signaling (SDP or equivalent).
• Avoid predictable SSRCs: Don’t use easily guessable or sequential SSRCs if security through obscurity helps mitigate simplistic attack vectors in your deployment.
• Monitor for SSRC collisions: Implement runtime detection of SSRC conflicts (two active sources with same SSRC) and handle them by reassigning SSRCs and sending RTCP reports as needed.
• Align SSRC management with session signaling: Ensure SSRCs advertised in session descriptions (SDP/offer-answer) match runtime assignments and update session signaling on mid-session SSRC changes.

Implementation tips

• Centralize SSRC generation: Provide a single SSRC factory in Foo DSP so all modules request SSRCs from one source, ensuring uniqueness and consistent policies (persistence, reseed logic).
• Seed RNG with sufficient entropy: Use OS-provided cryptographic randomness to seed SSRC generation to reduce collision probability across devices.
• Track SSRC lifecycle: Maintain metadata for each SSRC: creation time, associated stream id, purpose (primary/RTX/FEC), last active timestamp, and restart count for diagnostics.
• Expose configuration: Allow operators to configure SSRC persistence windows, whether to reuse SSRC after brief pauses, and RTX/FEc SSRC assignment policies.
• RTCP integration: Emit regular RTCP Sender Reports tied to the correct SSRC and handle Receiver Reports to assess packet loss, jitter, and round-trip time per SSRC.
• Testing and tooling: Provide tools to simulate SSRC collisions, network interruptions, and multi-source scenarios; include logging that maps SSRCs to human-readable stream identifiers.
• Interoperability checks: Test Foo DSP with common endpoints and SFUs to ensure SSRC behavior (multiplexing, RTX) aligns with expectations in diverse environments.
• Document expected behaviors: In developer and operator docs, clearly state when Foo DSP will change SSRC, how collisions are resolved, and how to correlate SSRCs with higher-level stream IDs.

Quick checklist before deployment

• Centralized SSRC generator in place
• Cryptographically seeded RNG used
• Distinct SSRCs for primary/RTX/FEC
• RTCP reporting implemented per SSRC
• Collision detection and handling enabled
• Session signaling reflects runtime SSRCs
• Monitoring/logging maps SSRC → stream

Date: March 4, 2026