network bandwidth analysis with iperf

yum install iperf

Before going ahead with the test, lets understand some networking concepts related to speed test.

Network Throughput

Transfer rate of data from one place to another with respect to time is called as throughput. Throughput is considered a quality measuring metric for hard disks,network etc. Its measured in Kbps(Kilo bits per second),Mbps(Mega bits per second),Gbps(Giga bits per second.)

TCP Window

TCP (Transmission Control Protocol), is a reliable transport layer protocol used for network communications. How TCP works, is beyond the scope of this article. TCP works on a reliable manner, by sending messages and waiting for acknowledgement from the receiver.

Whenever two machine's are communicating with each other, then each of them will inform the other, about the amount of bytes it is ready to receive at one time.

In other words, the maximum amount of data that a sender can send the other end, without an acknowledgement is called as Window Size. This TCP window size affects network throughput very badly sometimes. Lets take an example.

Suppose you want to send a 500MB of data from one machine to the other, with the tcp window size of 64KB.

Which means for sending the whole 500MB data, the sending machine has to wait 800 times for an acknowledgement from the receiver.

500MB / 64KB = 800

So you can clearly see that, if you increase the Window size a little bit to tune TCP, it can bring significant difference to the throughput achieved.

Suppose you have a windows machine and want to measure the speed between it and another Linux machine, then you need to make one as client, and another as the server. Lets see how.