Simulate network speeds using Fiddler

Question

I am using Fiddler and want to simulate different network speeds

Is there any published data that I can use to simulate different speeds using the delay value ?

Following is default code of Fiddler to simulate 56kb modem speed.

if (m_SimulateModem) {     // Delay sends by 300ms per KB uploaded.     oSession["request-trickle-delay"] = "300";      // Delay receives by 150ms per KB downloaded.     oSession["response-trickle-delay"] = "150";  } 

I want the delay values for 256kbps, 512kbps, 1Mbps etc...

Answer 1

This is simply a math problem.

Assuming that content is available instantly (e.g. you're playing it back from the AutoResponder) then the only delay is controlled by request-trickle-delay and response-trickle-delay flags.

There are 1000 milliseconds per second.

So, if you want to gate the connection to 1 megabyte per second, you would use a delay of 1 ms. If you want to gate it to 512 kilobyte per second, then use a delay of 2 ms. For 256 kilobytes per second, use a delay of 4 ms.

Keep in mind that bandwidth is often measured in bits per second rather than bytes per second. So if your goal is to measure things in bits-per-second, then multiply each value by 8.

Answer 2

I made changes to request-trickle-delay and response-trickle-delay that EricLaw Recommended. I used SpeedTest.Net to valaidate the changes I made. They didn't match up perfectly. For example I expected that if I set Trickle Delay values to 8 I would get download speed of 1 Mbps, but actually got 2.05 Mbps. Based on EricLaw's answer at least I was able to identify a pattern. Thanks Eric.

After each change to the Fiddler CustomerRule.js file I re-enabled "Simulate Modem Speed". FYI, when you make a change to the CustomerRule.js file the "Simulate Modem Speed" is disabled. So you must re-enable the setting.

I added a few images of results from SpeedTest.net.

Below are the results for each setting change:

Fiddler Settings

Here I set request-trickle-delay and response-trickle-delay to 16. As you can see I received 1.03 Mbps

Here I set request-trickle-delay and response-trickle-delay to 32. As you can see I received 0.52 Mbps