Hong Kong is the sole geographic exception: it experiences no measurable slowdowns when accessing the foreign Internet, and Chinese mainland receivers accessing Hong Kong as a sender averaged only ~3 hours of slowdown per day — compared to 5–17 hours for US, European, and most Asian senders — making it an effective high-performance relay between mainland China and the rest of the world.

Hop-by-hop bottleneck localization showed that in more than 71% of measured paths the first lossy hop is located deep inside China (beyond the border), with only 34.45% of bottleneck hops coinciding with the GFW hop as detected by RST injection probing — suggesting Chinese ISP infrastructure underprovisioning rather than GFW intervention as the primary cause.

§5, Figure 13 evaluation

The bottleneck exhibits strong and consistent diurnal patterns: 80–95% of receiver–sender pairs show a standard deviation of less than 3 hours in daily slowdown duration, and the patterns persist unchanged across weekends and national holidays (May 1–2 and October 1 national day). Packet loss is strictly asymmetric — occurring only for traffic entering China (inbound data and outbound ACK packets), not for traffic leaving China.

§4.2 Observation 2, Observation 3, Figure 10 evaluation

The Great Bottleneck of China affects 79% of measured receiver–sender pairs, with more than 70% of those pairs suffering throughput below 1 Mbps for more than 5 hours every day. M-Lab NDT data independently corroborates this: in 64% of 75,464 tests from China, download speed was below 500 kbps.

§3, §4.2 Observation 1, Figure 5 evaluation

A/B testing across HTTP, HTTPS, VPN, and Shadowsocks traffic found no measurable difference in packet loss rates, ruling out censorship-targeted protocol throttling as the cause. Even at probe rates as low as one packet per 10 seconds, loss rates were similar across all protocol variants, indicating no per-connection or per-protocol speed throttling by the GFW.

§4.2 Observation 4, Experiment 3 detection

During the June 2025 Iran shutdown, circumvention tool performance diverged sharply by transport design. Psiphon's multi-protocol architecture sustained 1.5 million concurrent users—roughly one-third of its normal Iranian base. Lantern's "proxyless" protocol (domain-fronting via CDN, ~40% of Lantern's Iranian traffic) showed moderate success. Tor usage collapsed during the blackout but bridge connections surged and rebounded quickly after lifting. BeePass (serving 500k+ daily users at shutdown onset) used live A/B testing of port/obfuscation-prefix combinations to probe the censors' blocking parameters in real time. The Ceno Browser's P2P network grew from 600 active peers on June 13 to ~8,000 by July 11, indicating that decentralized fallback paths stayed up even during peak blocking.

2025-iran-shutdown-measurement §Tool Performance dpithrottling

Article 19 documents that Iran's National Information Network (NIN / SHOMA) was designed with explicit reference to China's Great Firewall as a model, with institutional mirroring: Iran's Supreme Council of Cyberspace parallels China's Cyberspace Administration of China, and both governments share a "cyber sovereignty" doctrine used to justify domestic content controls and cross-border technology transfer. The report frames Iran's filtering infrastructure as deliberately architected to replicate GFW capabilities, not as an independently developed system.

2026-article19-tightening-the-net §2, §3 dpisni-blockingdns-poisoningip-blockingbgp-hijackthrottling

Article 19 documents that Iran combines technical filtering with formal coercion of major foreign platforms (including Telegram, Instagram, and WhatsApp) to comply with content removal orders under threat of full blocking. The report notes that Iran's 2022 Women Life Freedom protests accelerated platform blocking when foreign operators refused compliance, demonstrating that the censorship system operates in two modes: coerce-and-allow for compliant platforms, block for non-compliant ones. Domain fronting via these platforms is therefore subject to sudden revocation if political conditions change.

2026-article19-tightening-the-net §6 ip-blockingdns-poisoningthrottling

The report maps specific Belt and Road Initiative Digital Silk Road projects through which Chinese technology vendors have transferred censorship and surveillance infrastructure to Iran, including fiber backbone investments, data-center co-location agreements, and equipment supply chains. Specific vendors named include Huawei and ZTE as network infrastructure providers, with the report noting that equipment exports include filtering-capable hardware that Iran's ISPs have deployed at network choke points.

2026-article19-tightening-the-net §4, §5 dpisni-blockingthrottling

The April 2026 enforcement cycle created a resource-scarcity feedback loop: upstream providers cut lines with no obligation to refund resellers, newly acquired replacement resources can themselves be reported and cut within days, and stable-resource availability windows are described as "越来越短" (increasingly short) while costs rise concurrently. The overall effect is systemic capacity contraction forecast to continue through at least May 2026.

2026-ermao-april-airport-outage §这轮波动到底发生了什么 / §四月后的趋势判断 ip-blockingasn-blackholingthrottling

An infrastructure-level adversary must balance watermark detectability against connection stability: the paper's threat model requires a minimum shaping rate rmin to prevent Tor circuit stalls, timeouts, or circuit replacement, and notes that repeated poor-throughput events can cause the circuit to be abandoned before sufficient watermark evidence is accumulated. This detectability–stability trade-off constrains the practical attack to macroscopic (30-second) modulation periods rather than fine-grained packet-level timing manipulation.

2026-fan-activeflowmark-assessing-tor §III.A, §VII.A flow-correlationtraffic-shapethrottling