进入全球课堂
More than 1 million international students are enrolled in American universities, 其中几乎一半来自中国, 根据来自 EducationData.org. 在2020年, many of these students were required to attend classes remotely from their home countries, due to a mixture of controversial student visa policy changes, 家庭的偏好, 以及旅行限制. This created large challenges for universities as they worked to reliably deliver online video instruction around the world. But these are not new challenges for either schools or students. 约35万美元.S. 每年都有大学生出国留学, and many of them take online courses from their home university while overseas. The scale was new, though, so we were able to learn a great deal.
中国提供了一个特别有趣的案例研究, due to both its huge population size and the difficulty of operating in its networks. All network traffic in China is routed through 10 national hubs. 直到2015年, all Chinese internet traffic was routed through three hubs in Beijing, 上海, and Guangzhou; to this day, those three hubs connect the Chinese network to the global internet via undersea fiber-optic cable. Those hubs also operate the world’s most sophisticated censorship apparatus—the so-called Great Firewall of China—to block or disrupt foreign websites and internet services the government deems undesirable, 最著名的, 所有谷歌和Facebook的产品.
A consortium that includes Google and Facebook had plans to run the Pacific Light Cable Network, a 120Tbps fiber-optic cable system that was to span from Los Angeles to Hong Kong. 然而，这些计划被美国政府否决了.S. 联邦通信委员会, and the undersea cable will stop short of Hong Kong and end at Taiwan and the Philippines. 在中国, it’s illegal to host a website without a government-approved Internet Content Provider (ICP) license, 而且这些债券很少发行给非中国实体. 中国最大的流媒体公司是爱奇艺, 但其ICP许可证由另外两家中国公司持有, 该公司在2018年提交给美国证券交易委员会的IPO文件中详细说明了这一点.美国证券交易委员会.
Given this background, how might schools reliably deliver streaming media to students in China? One option is to establish a presence within China to bypass the bottleneck of the Beijing/上海/Guangzhou ingress points and firewalls. 这需要一个拥有ICP许可证的中国合作伙伴. 例如, Coursera partnered with Chinese internet company NetEase in 2013 to host a mirror of Coursera videos within China, 有效地将其CDN扩展到防火墙之外. Duke University struck a partnership with Wuhan University in 2011 to form Duke Kunshan University. It began hitting its stride in the last few years and could ultimately provide the same benefit.
A less ambitious alternative is to optimize your video to traverse the firewalls and the bottlenecks. The feedback I’ve gotten over the past year says that maintaining a rung on your encoding ladder with a bitrate of, 最多, 550Kbps total will usually allow video to be smoothly playable at normal speed during off-peak hours; students overseas will struggle to watch video at faster playback rates since the data rate increases apace the speed. My lowest rung is 148K, which will allow students to play video smoothly at 1.5倍的速度，即使在高峰使用时间. Students have also reported that their internet speeds are much worse during peak workday hours overseas, although I wasn’t able to determine whether that was a bottleneck problem at ingress, 最后一英里, 或两个. And finally, overseas VPN usage dramatically reduces measured throughput. vpn在中国可以说是非法的, so I would advise schools to absolutely avoid anything on the internet that’s blocked by the Great Firewall.
An attractive hybrid approach would be to use peer-to-peer (P2P) streaming, in which students would share among themselves video data that has traversed the firewall instead of fetching it through the firewall each time. Since educational video tends to be viewed in batches as cohorts of students go through the course, 它很适合这个模型, 中国的网络架构也是如此, in which P2P is a proven technology of platforms like PPTV and PPS.
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