Mobility

Evaluation: Reachability after interface switch

The goal of the evaluation was to check how long it takes PTP to be available again after an interface switch (e.g. wifi to mobile network).

Setup

• Two devices: Android smartphone (Nexus 5X) and a server running Linux
• Android smartphone: runs Tor 0.2.8.9, Doze disabled for PTP (Settings -> Battery -> Battery Optimization -> PTPEvaluationApp -> Not optimized), screen was off during evaluation, started with fully charged battery
• Server: runs Tor 0.2.8.11
• PTP settings: IsAliveTimeout 30s, IsAliveSendTimeout 20s

Evaluation process

• Execute run.sh in evaluation/connectivity
• Change connectivity when requested ("Change connectivity and press enter")
• Press Enter
• Wait until reconnecting is successful

Results

datetime	from	to	time to reconnect
20.12.16 22:21	wifi	4g	36s
20.12.16 22:29	4g	wifi	44s
20.12.16 22:33	wifi	4g	26s
20.12.16 22:36	4g	wifi	44s
20.12.16 22:39	wifi	4g	31s
20.12.16 22:42	4g	wifi	39s
21.12.16 19:18	wifi	4g	36s
21.12.16 19:26	4g	wifi	53s
21.12.16 19:29	wifi	4g	36s
21.12.16 19:32	4g	wifi	42 s

Conclusion

Implemented mechanisms to detect a broken connection and close the respective Tor circuit seem to work. The lower bound of the time to reconnect is the value of the IsAliveTimeout configuration option. The option determines after which time a circuit gets closed if the remote end doesn't answer a message.