I intend to write an application where I will be needing to calculate the network bandwidth along with latency and packet loss rate. One of the constraints is to passively measure the bandwidth (using the application data itself).
What I have read online and understood from a few existing applications is that almost all of them use active probing techniques (that is, generating a flow of probe packets) and use the time difference between arrival of the first and last packets to calculate the bandwidth.
The main problems with such a technique are that it floods the network with probe packets, which runs longer and is not scalable (since we need to run the application at both ends).
One of the suggestions was to calculate the RTT of a packet by echoing it back to the sender and calculate the bandwidth using the following equation:
Bandwidth <= (Receive Buffer size)/RTT.
I am not sure how accurate this could be as the receiver may not always echo back the packet on time to get the correct RTT. Use of ICMP alone may not always work as many servers disable it.
My main application runs over a TCP connection so I am interested in using the TCP connection to measure the actual bandwidth offered over a particular period of time. I would really appreciate if anybody could suggest a simple technique (reliable formula) to measure the bandwidth for a TCP connection.
It is only possible to know the available bandwidth by probing the network. This is due to that a 80% utilized link will still send echo-packets without delay, i.e. it will appear to be 0% occupied.
If you instead just wish to measure the bandwidth your application is using, it is much easier. E.g. keep a record of the amount of data you have transferred in the last second divided into 10ms intervals.