How fast is your Internet?
“Speed”, when it comes to network connections, is measured by two different things: latency and bandwidth.
Latency is the measure of how quickly a little bit of information can get from one end of a connection to the other (and usually, back again). The “ping” program, which you may have used, is one tool which measures latency. Latency is generally expressed in milliseconds (e.g., “30ms round-trip time on average”)
Bandwidth is the measure of how much data you can hurl down an Internet connection in a particular length of time. Bandwidth is usually measured in some multiple of bits-per-second, for example, megabits per second (Mbps).
Latency and bandwidth are independent. You can have a very high-bandwidth connection that is also high-latency. High bandwidth is good, high latency is bad. Similarly, you can have a low-latency connection which isn’t very high-bandwidth.
Some examples: GPRS and EDGE are comparatively high-bandwidth, but also high-latency. As such, even though you can download files relatively quickly, browsing the web feels sluggish. High-latency connections mean that the “little” things—such as requesting, then downloading, a web page—take longer. For each image on a web page, your browser has to connect to the server and request it, and the server has to send it back to you. Even if it’s a tiny image, a high-latency connections makes that tortuous.
Similarly, you can have a low-latency connection which is either high- or low-bandwidth. ADSL connections are fairly low-latency, when they’re working properly, but the amount of bandwidth can vary from 512 kilobits per second (that’s half a megabit) up to fifty megabits per second and beyond. Browsing the web, you’re not likely to notice any difference between a 512kbps and 50Mbps connection of the same latency, assuming that’s all you’re doing. If you’re streaming video, downloading the latest Ubuntu release, grabbing an e-mail attachment and browsing the web, then you’ll notice the difference.
An oft-used analogy is that of a pipe (in fact, Internet connections are often called ‘pipes’ by networking geeks). Bandwidth is the measure of how big the pipe is, while latency is the measure of how fast the water is travelling down it. High-bandwidth high-latency is a big pipe with slow-moving water. Low-bandwidth high-latency is a trickle of water through a tiny pipe, while low-bandwidth low-latency is a tiny pipe with water pushed through it very quickly. You get the idea.
So when you see an advert for a “fast” Internet connection, just stop to ponder: why is it only ever the bandwidth that’s mentioned? If the bandwidth is the key factor as the adverts suggest, what’s the point in a “fast” connection if you can’t actually use it?
