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High-scale cleartext RTP (-media_scale)

Full documentation (English): high-scale-cleartext-rtp.md — architecture, rationale (XDP vs userspace), tuning, acceptance criteria, and tests.

Gossipper can generate many parallel cleartext synthetic RTP streams without one goroutine and one time.Ticker per stream. Use this for load tests toward a single SBC or media gateway (for example 10k PCMU streams at 20 ms).

When to use

Use -media_scale Do not use
rtp_stream="synthetic,…" in scenarios SRTP / DTLS (-media_srtp)
-rtp_send with optional -rtp_streams N PCAP, mic, echo, rtpcheck
Send-only toward one or few peers Per-packet HEP RTP mirror on hot path

This path does not use XDP/eBPF. Throughput is improved by a central scheduler, buffer reuse, and batched UDP send (sendmmsg on Linux).

Flags

Flag Description
-media_scale Enable the scale RTP engine
-media_iouring With -media_scale: send RTP batches from the scheduler (Linux sendmmsg; fewer goroutines). Or GOSSIPPER_MEDIA_IOURING=1
-rtp_streams N With -rtp_send -media_scale, start N parallel streams (local ports step by 2)

-media_scale cannot be combined with -media_srtp.

Standalone example

# 1000 PCMU streams to one SBC (lab)
gossipper sipp -rtp_send -media_scale -rtp_streams 1000 \
  -rtp_addr 10.0.0.5:30000 -rtp_codec PCMU/8000 -rtp_freq 20 -i 10.0.0.1

Standard scenario (SIP + 10k RTP)

gossipper sipp -sn invite_media_scale -rsa SBC:5060 -i LOCAL -p 5060 -m 10000 -l 10000 -r 20

-media_scale is turned on automatically for -sn invite_media_scale. See high-scale-cleartext-rtp.md.

Custom scenario example

<exec rtp_stream="synthetic,0,0,PCMU/8000,20"/>

Run with -media_scale (or use the built-in name above). Remote RTP address comes from SDP (ParseAudioEndpoint).

OS tuning

Before large runs (especially 5k–10k streams):

  1. File descriptors: ulimit -n ≥ 20000 (one UDP socket per stream plus SIP).
  2. UDP buffers: apply sysctl values similar to Homer:
sudo sysctl -w net.core.rmem_max=33554432
sudo sysctl -w net.core.wmem_max=33554432
sudo sysctl -w net.core.wmem_default=4194304
sudo sysctl -w net.core.netdev_max_backlog=250000

Or use scripts/tune-udp-sysctl.sh / examples/sysctl/gossipper-high-scale.conf.

  1. CPU: set GOMAXPROCS to the number of physical cores on the generator host.

Acceptance checks

  • summary / JSON: media.rtp_packets_sent ≈ streams × (1000/freq_ms) × duration_seconds
  • Process goroutine count stays O(workers), not O(streams)
  • No sustained sendto errors on the generator (dmesg, ss -s)

Architecture

See internal/media/scale_engine.go: min-heap scheduler (1 ms tick), sender worker pool, per-stream UDP socket bound to [media_port].