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More Pandemic and the Internet interactions

已有 2206 次阅读 2021-6-2 01:15 |个人分类:S and T|系统分类:海外观察

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More Pandemic and the Internet interactions

During this pandemic, use of “ZOOM” software as a communication tool had a tremendous increase. This constituted a stress test for the workings of the Internet which it more or less successfully passed. However, there is a back story to this episode which most users of the Internet and zoom are not aware of. It is worth reporting to let the public know something about how “ENGINEERING” works to make our life more comfortable and of high quality. Previously, I wrote about the workings of GPS as a triumph of engineering http://blog.sciencenet.cn/home.php?mod=space&uid=1565&do=blog&quickforward=1&id=1057130. This article illustrates another example, i.e., how the Internet works? I am indebted to my colleague Professor Weibo Gong of UMass Amherst to bringing this to my attention. But he is too modest and declined my invitation for him to write about this. Thus, readers should thank him for any insight you gleam from this account. I am of course shall be responsible for any mistakes in this blog article.

For readers in the US (and possibly in China) who watches talk shows on TV, you must have noticed during the past year occasionally a guest’s video image will freeze and/or his voice not synchronized with his mouth shown on video. The host of the talk show will of course notice this and mention this as a technical glitch to be fixed. This is both “yes and no”! It is simply the Internet undergoing an involuntary stress test.

What happened is that there are too many people using the Internet for zoom meetings to transmit all video images and a slight traffic jams result. This is understandable. However, alert readers may immediately point out how come this never happens to the host when he is speaking? This is because the Internet uses two different speed for uploading and downloading of data. When you watch a talk show. The host uses the faster download speed to transmit his voice and video image while the guests use the slower upload speed to do the same. When a traffic jam results from too much traffic and not enough bandwidth, the Internet uses an algorithm known as AIMD (Additive Increase and Multiplicated Decrease) to allocate and adjudicate between supply and demand. This bring about occasional faulty transmission of some video and audio messages when AIMD is working under stress. By the way, this AIMD algorithm was invented by two former Harvard Ph.D graduates in Applied Mathematics and Engineering Science named Dahming Chiu and Raj Jain https://en.wikipedia.org/wiki/Additive_increase/multiplicative_decrease. Dahming did his ph.d thesis with me long ago and now teaches at the University of Hongkong. Very few academics can claim such distinction of inventing a product/service that is used so widely and benefits mankind so much.




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