People often compare the Internet to an "information highway", but a more accurate metaphor should be an "information highway network". The Internet is as complex as the road network in reality, with a backbone network as fast as a highway connecting two places, and a network environment as bad as a difficult and rugged mountain road. And transferring data over the Internet is like driving from one place to another.
Now let's use this metaphor to explain three very important characteristics of Internet transmission: delay, packet loss, and jitter.
Suppose we now have 100 vehicles driving from Beijing Bird's Nest to Shanghai Oriental Pearl Tower, and one car departs every minute.
time delay
"Delay" refers to the average time for each car to drive from the Bird's Nest to the Oriental Pearl Tower.
Obviously, it is definitely faster for the convoy to take the expressway than to take various small roads, and the route from the Bird's Nest to the expressway also has a great influence. If it gets stuck on the third ring road, it will take several hours up.
So this value is related to the driving route chosen by the team. The same is true for Internet transmission. There are often many optional paths between two points that need to transmit data, and the delays of these paths often vary greatly.
packet loss
"Packet loss" means that some cars cannot reach the end point within the valid time, and may even never reach the end point.
Some cars may be stuck on Beijing's third ring road forever, and some cars may have accidents halfway.
If five of our one hundred vehicles fail to arrive in Shanghai on time due to various reasons, the "packet loss rate" of our convoy transmission is 5%. Yes, internet transmission is the same, it is not 100% reliable, there will always be data that cannot be transmitted to the destination on time.
jitter
"Jitter" refers to differences in the order, interval and departure of cars.
Although our 100 vehicles departed every minute at equal intervals in Beijing, they did not arrive in Shanghai one by one in order, and there may even be vehicles that departed later than those that departed earlier. to the situation.
The same is true for Internet transmission. If the audio and video data are simply played out in the order received, distortion will occur.
Latency, packet loss, and jitter are three unavoidable characteristics of the Internet, an information highway network. In the previous scenarios of e-mail, web browsing, and text chat, these three characteristics were not too big of a problem. After all, people could accept that e-mails arrived at the other party’s mailbox a few minutes late. But in the case of real-time audio and video communication, let alone a few minutes, even if there is only a few seconds of delay, the experience of audio and video communication will be greatly reduced.
Reprinted: https://zhuanlan.zhihu.com/p/21968527