[Computer Network] Understanding of Delay-Bandwidth Product (Easy to Understand Graphical Illustrations)

1. Definition of delay-bandwidth product

Delay-bandwidth product = propagation delay * bandwidth

• Propagation delay: The time it takes for an electromagnetic wave to propagate a certain distance in a channel
• Bandwidth: the "highest data rate" that a certain channel can pass, the unit is the data rate unit bit/s, that is, "bits per second"

2. Give examples to understand

Assume that a certain channel

• Bandwidth: 2bit/s, that is, the channel can pass two bits per second
• Propagation delay: 2s
  , the delay bandwidth product is: 2bit/s * 2s = 4bit, which means the channel has a total of 4 bits
  
• The two small red dots in the first picture represent two bits , which are ready to be sent at 0 seconds
• The two small red dots in the middle of the channel in the second picture represent the bits being sent in the channel (because the propagation delay is assumed to be 2s, it reaches the middle of the channel at the 1s)
• The last two red dots in the third picture represent the two bits arriving at the end point , and the two small red dots in the middle represent the bits sent in the first second . At this time, there are a total of 4 bits
  in the channel. To sum up: the delay bandwidth product of this channel is 4 bits , so the delay-bandwidth product is also called: "link length in bits"