Glossary
A quick reference for live streaming and WebRTC terms — latency, ingest, delivery, and billing concepts explained.
- WebRTC
- A browser standard for real-time audio/video/data with sub-second latency and built-in encryption, used by PPCDN for both ingest and playback.
- WHIP
- WebRTC-HTTP Ingestion Protocol — a standard way to publish a live stream into a WebRTC server over a single HTTP request.
- WHEP
- WebRTC-HTTP Egress Protocol — the standard counterpart to WHIP for playing a stream out over WebRTC in the browser.
- SRT
- Secure Reliable Transport — a UDP-based contribution protocol with error recovery and low latency, used by PPCDN as an alternative ingest.
- RTMP
- Real-Time Messaging Protocol — the legacy ingest protocol built on TCP; still widely supported by encoders but higher-latency than WHIP/SRT.
- HLS
- HTTP Live Streaming — a segmented HTTP protocol with several seconds of structural latency; good for scale/VOD, not for live interaction.
- Simulcast
- Publishing one stream at multiple resolutions/bitrates so the server can deliver the best layer per viewer without re-encoding.
- ABR (Adaptive Bitrate)
- Automatically stepping a viewer up or down between quality layers based on live packet loss and RTT to keep playback smooth.
- P2P (peer-to-peer)
- Delivering media directly between the publisher and a viewer, bypassing edge servers to cut latency and egress cost.
- NAT traversal
- The techniques (STUN/ICE) that let two peers behind routers establish a direct connection; symmetric NAT or CGNAT can make it fail.
- TURN
- A relay server used when direct P2P is impossible. PPCDN deliberately does not relay P2P and falls back to the Edge path instead.
- DTLS-SRTP
- The mandatory encryption for WebRTC media, providing end-to-end confidentiality between peers.
- Origin / Edge
- The two-tier CDN topology: Origin ingests the publish stream reliably, Edge pulls from Origin and serves viewers nearby.
- End-to-end latency
- The time between a frame being captured at the publisher and shown at the viewer, measured in PPCDN via in-band timestamps.
- Jitter
- Variation in frame arrival time. High jitter hurts the experience more than a slightly higher average latency.
- Rebuffering
- When playback stalls waiting for data. ABR and simulcast layers are used to minimize rebuffering on weak networks.
- IDR frame
- A keyframe that resets the decoder — PPCDN switches simulcast layers on IDR boundaries to avoid visible artifacts.
- HEVC / H.265
- A newer video codec that delivers similar quality at roughly 30% less bitrate than H.264 where supported.
- CDN
- A network of servers that delivers media from locations close to viewers to reduce latency and origin load.
- Egress / downstream traffic
- Data delivered from servers to viewers. PPCDN bills downstream at $0.0244/GB and removes it entirely for successful P2P connections.
- SLA
- A measurable service target. PPCDN tracks a daily P2P latency SLA (P80 ≤ 300ms, P99 ≤ 2s) for display and alerting.
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