How Does Latency Affect Maximum Download Rate?

Latency is an important factor in determining maximum download rates for small files; however, it is not very important for large file downloads. Latency measures the time it takes to establish a connection between two systems. Bandwidth measures how quickly data can be transferred between two connected systems. The combination of latency and bandwidth in a data transfer creates what person perceives as Internet connection speed. A lower latency connection improves the maximum download rate by eliminating the amount of time spent not downloading anything in between different data transfers.

Latency, or ping, is the time it takes for a data request to leave a computer, get to another computer over the network or Internet and return to the original computer. With file downloads, the latency is how long it takes for the download to start after a computer makes the information request. Latency is important when it comes to programs that are constantly talking back and forth with other devices. The back and forth files take split seconds to download, and the download speed can be increased by decreasing the time between transfers. Lower latency reduces the time in between requests, thus allowing the next download to begin sooner.

Bandwidth is the measurement of how much data can be sent at once. If the Internet was a highway, the bandwidth would measure how many lanes the highway is wide. Bandwidth is the most important factor when transferring large files that are a one-way communication. Once the transfer has started, the bandwidth becomes the more important factor.

The relationship between latency and bandwidth determines whether we consider an Internet connection to be fast. Latency doesn't affect bandwidth, but insufficient bandwidth can reduce latency. A high-latency, high-bandwidth connection would be slow to start downloading a Web page but would load quickly as soon as the download starts. A user loading a page with a high-latency, high-bandwidth connection that requests a page download experiences a page that hangs on a blank page for a moment and then loads almost instantly. A low-latency, low-bandwidth connection would quickly start loading a Web page but would take a longer time to finish. There is a cross-section file size determined by how a connection's latency and bandwidth relate -- anything smaller than a certain size will load faster with a lower latency, and anything larger will load faster with higher bandwidth. For example, a 1KB file would download much faster on a connection that has a 25ms ping and a 2Mbps bandwidth rating than it would on a connection with a 250ms ping and a 50Mbps bandwidth rating. Both connections have enough bandwidth, so the bandwidth isn't a factor.

Latency is relevant in smaller tasks, whereas bandwidth is relevant in larger tasks. A lower latency connection would be better for doing things like online gaming, instant messaging, teleconferencing and light website browsing. The higher bandwidth connection would be better for downloading large files, streaming videos and viewing complex, interactive websites.