To achieve effective data transfer mechanism, I need to find out how many bits can fill up a network link.

Let me explain the situation, Once I send a data(application protocol) it will reply a ACK after it process the data (in application layer) . If the RTT is high (Like 500 ms RTT) it takes too much time to send a ACK back. Until the ACK is received data will not being sent and it is in idle mode. To rectify the situation , I need to flight some data in-between intervals.

So I decide to transfer the data until the bandwidth delay product value(how many bits can fill up a network link) is exhaust by sent data size

BDP = Bandwidth(bits per sec) x RTT ( in secs).

How to find the network bandwidth of the device. Is there any Windows API or other ways to finds the bandwidth of link ?

PS : I am newbie to network programming

CodePudding user response：

You do not calculate bandwidth. The bandwidth is a property of the network interface. A 100 Mbps ethernet interface always has a 100 Mbps bandwidth. You are using the incorrect term.

If you are using TCP, the sender will constantly increase the send/congestion window until there is a problem, then it exponentially reduces the window size, and again starts increasing it until there is again a problem, repeating that over and over. Only a sender will know this window.

The receiver has a buffer that is the receive window, and it will communicate the current window size to the sender in every acknowledgement. The receive window will shrink as the buffer is filled, and grows as the buffer is emptied. The receive window determines how much data the sender is allowed to send before stopping to wait for an acknowledgement.

TCP handles all that automatically, calculating the SRTT and automatically adjusting to give you a good throughput for the conditions. You seem to want to control what TCP inherently does for you. You can tweak things like the receive buffer to increase the throughput, but you need to write your own transport protocol to do what you propose because you will overrun the receive buffer, losing data or crashing the receiving host.

Also, remember that TCP creates a connection between two equal TCP peers. Both are senders and both are receivers. Either side can send and receive, and either side can initiate closing the connection or kill it with a RST.

CodePudding user response：

winapi GetIpNetworkConnectionBandwidthEstimates() gets "historical" BW "estimates" for a network connection (this is more relevant than the whole interface/link) on the spec'd intf.