S96 dynamic IP obfs4 bridge performance insufficiency

This issue describes a potential usability issue with S96 dynamic IP address obfs4 bridges. The network connectivity between these bridges hosted at OVH and Tor's China vantage has an insufficient performance level to get Tor bootstrap consistently.

Tor like any network application assumes a certain level of network performance to operate correctly. However, the dynamic IP obfs4 bridge currently set up have a download speed of 5-20 KByte/s during some time of the day. This speed makes its end-user experience inconsistent, and sometimes stop working(This is observed by both @cohosh and me when the bridge is unable to finish bootstrap and progress stuck at 50%).

Additional diagnose(see below) show ping to Sr2CobaltPluto bridge provided by @irl have a packet loss of 8%. For an ordinary TCP stack, this packet loss level will almost always result in a slow transfer speed.

The root cause of this issue is the TCP stack used is not designed to sufficiently compensate for packet loss; network link to OVH instance is throttled(intentional or not) with 1. transit via congested AS4134 CHINANET backbone network (as presumably a deprioritized traffic), 2. traffic between instance located Europe and vantage point took a detour at the US(see traceroute in the link above).

This issue is marked as confidential to prevent the IP address of our vantage point become public. (traceroute info removed to make this ticket public.)