Internet Speed Measurement
Internet speed can be broken down into three distinct categories: download speed (the speed a user can retrieve something from the Internet), upload speed (the speed a user can send something to a remote location on the Internet) and latency (the lag or length of time that occurs between each point during information transfer).
Download and upload speeds are measured in the number of bits (or bytes) per second transferred, while latency is measure in milliseconds (or thousandths of a second). To provide an extremely simplistic explanation, think of this measurement as comparable to a truck payload, such that a big truck can carry more than an economy pickup truck.
Upload and Download Speeds
The most common measurement usually quoted is the download speed, followed by the upload speed. For example, a cable company advertises 15 Mbps down/1.5 Mbps up, as compared to a T1 line, which advertises 1.5 Mbps down/1.5 Mbps up. (Note that a T1 line is very expensive and comes with a service level agreement that guarantees uptime and quality of service, whereas a typical cable internet connection does not.) This measurement can be thought of as the payload, or the amount of information that can be moved in a tractor trailer truck (15 tons) as opposed to a pickup truck moving 1.5 tons.
If a user is predominately interested in downloading large files (movies from Blockbuster or Netflix), the download speed is the primary concern. The higher the numerical value for download speed means the less time the movie will take to get from the Blockbuster's site to your computer. In other words, if you download a movie at 15 Mbps it will theoretically take 1/10th as long to download than if used a 1.5 Mbps connection.
The upload speed indicates what kind of performance you would expect if you were sending a number of high-resolution photographs as an email attachment or uploading them to a photo printing service.
In the above example, the tractor trailer truck was moving 10 times the data that the pickup truck was capable of handling--but there is an important factor that was ignored: What speed are both vehicles traveling at? For example, if the tractor trailer is stuck in traffic and averaging 5 mph while the pickup truck is speeding down the highway at 70 mph, the pickup truck is actually moving the data faster. In this example, the speed would equal latency.
Latency is critical to many Internet applications. VoIP (a service sold by Vonage among others) is highly dependent on your voice getting to your caller's ear quickly. If there were to be a delay of three seconds between the time you say hello and they hear the word, a phone call would be next to useless. Gaming, a popular pastime, is also extremely susceptible to lag (another common term for latency).
While it is doubtful that latency would be an issue with most consumer-grade Internet connections, using any of the satellite Internet services will introduce latency that will prevent VoIP from being used and add an additional challenge to many fast paced, online games.