I saw in Internet that Bandwidth-Delay product = Bandwidth * Round Trip Time = Send Window size + Receive Window Size.
As per definitions, Bandwidth Delay Product is the amount of data in transit within the time it takes for a sender to send a packet and receive acknowledgement. And send window determines the amount of data that can be sent without receiving acknowledgement. So , for me intuitively , the equation is----> send window size = bandwidth delay product. Unable to understand why receive window size plays any role here.
Can someone kindly explain ? Thanks.
Here is the interaction between Send and Receive Window Sizes:
First, Let's understand Send Window Limitation: If the send window size is smaller than the BDP, the sender cannot fully utilize the bandwidth. For example, if the BDP indicates you can send 1 MB of data before needing an acknowledgment, but the send window size is only 500 KB, you’ll only be able to send 500 KB worth of data before stopping and waiting for an acknowledgment, which limits throughput.
Receive Window Limitation: Similarly, if the receive window size is smaller than the BDP, the sender will be limited by the receive window size. Even if the sender’s window size is large enough to utilize the bandwidth, if the receiver cannot handle that amount of data (because its window size is too small), it won't be able to receive data at the full rate.
Now, let's look at Effective Window Size: The actual amount of data that can be in transit is constrained by the smaller of the two window sizes (send and receive). Therefore, for optimal performance, both window sizes need to be sufficiently large to match or exceed the BDP. If either window is too small, it can lead to reduced throughput and inefficient use of the network’s available bandwidth.
In summary, both the send window size and receive window size are critical because they together determine the maximum amount of data that can be in transit at any given time. The effective window size is limited by the smaller of the two, and ensuring that both are appropriately sized relative to the BDP is essential for achieving high network performance.
More Clarification: If you added the send and receive window sizes, it would not accurately reflect the maximum amount of data in transit. Adding the sizes might seem like it would give a larger number, but in practice, you cannot have more data in transit than the smallest constraint, because data cannot exceed the capacity of the receiver to handle it or the sender’s ability to keep track of it.
So, the formula to determine the data in transit does indeed use the minimum of the two window sizes:
Max Data in Transit=min(Send Window Size,Receive Window Size)
This correctly accounts for the limitation imposed by both sides of the communication.