A Case for Marrying Censorship Measurements with Circumvention

Routing traffic from a user on ISP-B through a peer relay on ISP-A (which applied only HTTP-level filtering and permitted HTTPS) produced the smallest page load times in most cross-ISP comparison runs, beating both HTTPS/domain-fronting and Tor. The performance gain is attributed to lower end-to-end latency on the intra-country cross-ISP path relative to international relay routes.

§3.2 / Figure 2c / Insight-3 evaluation ip-blockingdpi pk

Direct circumvention via HTTPS/domain-fronting from Pakistan achieved an average throughput of ≈1.5 Mbps, whereas static proxies located in the US, Europe, and Asia yielded less than 0.9 Mbps in most cases. Page load times for the YouTube homepage (≈360 KB) were significantly lower under the direct method, and a TCP slow-start model predicts throughput could reach ≈2 Mbps if the flow completed within slow start.

§3.2 / Figure 1 / Table 2 evaluation ip-blocking pk

Across two major Pakistani ISPs, blocking mechanisms varied substantially for the same URL: ISP-A applied HTTP-level blocking with redirection to a block page, while ISP-B deployed multi-stage blocking combining DNS-level resolution to localhost and independent HTTP/HTTPS request dropping. A single ISP also used different filtering techniques for different URL categories (e.g., YouTube vs. HTTPS-accessible sites).

§3.2 / Table 1 evaluation dns-poisoningip-blockingdpi pk

C-Saw's design demonstrates that coupling circumvention capability with censorship measurement creates a self-reinforcing incentive loop: users opt in for improved page load times, their participation grows the vantage-point pool, and richer measurements enable finer-grained technique selection per ISP and URL. The system avoids requiring a pre-populated URL list by building a blocked-URL database dynamically from user-initiated requests.

§1 / §3.3 / §4.2 defense measurement-platform generic

In experiments using 200 back-to-back fetches of the YouTube homepage (≈360 KB), HTTPS produced lower page load times than Tor in most cases because Tor circuits do not optimize for performance and often select longer paths. Tor's page load times varied widely as circuits changed approximately every 10 minutes, producing a heavy tail in the latency distribution.

§3.2 / Figure 2a evaluation ip-blocking pk