Imagine this: You are the head of your company’s sales department. It’s 8:55 AM, and in five minutes you need to give a presentation to your CEO on last month’s sales figures. But as you download the files off your company’s server in the “cloud,” the progress bar remains stuck at 20%. You’ve got a 20 Mbps Metro Ethernet connection, but your computer is reporting a measly 1.3 MBps transfer rate. THAT’S IT! You’re going to be late and it’s your IT guy’s fault for choosing TPx as your Internet service provider. Hold on, don’t drop the “people’s elbow” on your IT guy just yet….

First, your computer is reporting your transfer rate to you in Megabytes-Per-Second (MBps) while your blameless carrier TPx is providing you bandwidth in Megabits-Per-Second (Mbps). To get Megabits from Megabytes you have to multiply your results by 8, so your actual transfer rate is 10.4 Mbps.

Well that is just fine, however 10.4 Mbps isn’t 20 Mbps. That is true – but unbeknownst to you, that guy from Marketing is streaming Gangnam Style for the 20th time that morning, which is consuming another 5 Mbps over your connection. So now you’re up to 15.4 Mbps. What’s happening to the last 4.6 Mbps?

Now it is time for the technical stuff…

1. Overhead (consisting of IP headers, error correction bits, and time stamps) consumes approximately 7% of your bandwidth.
2. Your maximum transfer rate is determined by the slowest link between your computer and the endpoint you are downloading from. That means the bottleneck could be somewhere out on the Internet, and therefore outside of your carrier’s network/control.
3. Most data transfers utilize TCP (transmission control protocol), which is designed for the reliable transmission of data, so it requires the receiver to send an acknowledgment to the sender. These acknowledgments will take up some of your bandwidth over the connection, and the ability of your computer to process these acknowledgments will affect your results.

The above considerations also apply to bandwidth speed test results. You will likely never see your entire port speed (in this case, 20 Mbps) when doing a bandwidth speed test.

I hope this has demystified bandwidth usage and saved your IT guy from unnecessary physical injury.

About the Author

Adam Czarkowski is a Director of Service Delivery for TPx Communications. His team manages the installation of TPx’s hosted communications and data services products. Adam has held a number of management roles in technical support and operations over his 17 years in the technology industry.