Hi all,

We are a group of researchers at University of California, Riverside who have been working on measuring the transnational network performance (and have previously asked questions on the mailing list). Our work has now led to a publication in Sigmetrics 2020 and we are eager to share some

interesting findings. 

We find China's transnational networks have extremely poor performance when accessing foreign sites, where the throughput is often persistently

low (e.g., for the majority of the daytime). Compared to other countries we measured including both developed and developing, China's transnational network performance is among the worst (comparable and even worse than some African countries).

Measuring from more than 400 pairs of mainland China and foreign nodes over more than 53 days, our result shows when data transferring from foreign nodes to China, 79% of measured connections has throughput lower than the 1Mbps, sometimes it is even much lower. The slow speed occurs only during certain times and forms a diurnal pattern that resembles congestion (irrespective of network protocol and content), please see the following figure. The diurnal pattern is fairly stable, 80% to 95% of the transnational connections have a less than 3 hours standard deviation of the slowdown hours each day over the entire duration. However, the speed rises up from 1Mbps to 4Mbps in about half an hour.

We are able to confirm that high packet loss rates and delays are incurred in the foreign-to-China direction only. Moreover, the end-to-end loss rate could rise up to 40% during the slow period, with ~15% on average.

There are a few things noteworthy regarding the phenomenon. First of all, all traffic types are treated equally, HTTP(S), VPN, etc., which means it is discriminating or differentiating any specific kinds of traffic. Second, we found for 71% of connections, the bottleneck is located inside China (the second hop after entering China or further), which means that it is mostly unrelated to the transnational link itself (e.g., submarine cable). Yet we never observed any such domestic traffic slowdowns within China.

Assuming this is due to congestion, it is unclear why the infrastructures within China that handles transnational traffic is not even capable to handle the capacity of transnational links, e.g., submarine cable, which maybe the most expensive investment themselves.

Here is the link to our paper:

https://www.cs.ucr.edu/~zhiyunq/pub/sigmetrics20_slowdown.pdf

We appreciate any comments or feedback. 

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Best,
Pengxiong Zhu
Department of Computer Science and Engineering
University of California, Riverside