At 64 bps FSK encoding over cellular voice, Dolphin achieves a bit error rate below 2% across all tested data sizes (100–5000 bytes), cellular providers, and geographic distances up to ~3600 miles. Rates of 128 bps and above cause BER to jump to 5–22%, making transmission too unreliable for practical use.

A 280-character tweet via Dolphin takes under 1 minute end-to-end; a 500-character email takes approximately 2.7 minutes (∼1 minute for ECDH secure-channel setup plus ∼1.7 minutes for data transmission). Performance was confirmed during a real Internet shutdown in Delhi, India, where a 300-character email transferred reliably in about 1 minute.

§5.2, §5.4, Figs. 8–10 evaluation

FSK-encoded Dolphin audio is distinguishable from normal human speech via offline amplitude analysis: Dolphin's mean signal amplitude is 0.4 (std 224) versus 205 (std 1590) for natural speech — approximately an order of magnitude lower — enabling classification by a telecom operator who records calls. The paper also notes that standard CRC checksums appearing periodically every chunk provide a unique detectable signature if the adversary attempts to decode the audio.

§6.5, Figs. 11–12 detection

Documented Internet shutdown events grew from 75 in 2016 to 213 in 2019 across 33 countries, with individual shutdowns lasting from hours to 472 days (Chad). These shutdowns completely sever IP connectivity, rendering all existing circumvention tools (Tor, VPNs, Shadowsocks, etc.) non-functional since they require at least partial Internet access to operate.

§1–2 deployment

An adversary introducing audio perturbations every 2.5 seconds (sufficient to corrupt each 20-byte chunk at 64 bps) degrades PESQ call quality to 1.6, below the 2.0 'unusable' threshold, making the attack self-defeating. However, targeting only acknowledgment windows (every ~12.5 s under Dolphin's default batch-of-5 configuration) achieves PESQ 3.6 — acceptable to human callers — while fully disrupting Dolphin data transfer.

§6.2 defense