# On airplane bandwidth and latency

Having recently used Virgin America to transport myself across the country, I was very pleased to have Internet access while I was in the air. This, however, is not the sort of airplane bandwidth and latency that I am going to talk about. Instead, I would like to discuss a comparison between the bandwidth and latency of typical Internet connections with those associated with taking a hard drive on an airplane.

Let's say we compare a high speed (\(15\mathrm{Mbit}\)) DSL connection to taking a moderately large hard drive (\(500\mathrm{GB}\)) on a plane for data rates between San Francisco and Boston (\(\approx 7\mathrm{hr}\)):

Bandwidth: DSL: \(15\frac{\mathrm{Mbit}}{\mathrm{s}}\) Airplane: \(\frac{500\mathrm{GB}}{7\mathrm{hr}} \times \frac{1\mathrm{hr}}{60\mathrm{min}} \times \frac{1\mathrm{min}}{60\mathrm{s}} \times \frac{8000\mathrm{Mbit}}{1\mathrm{GB}} \approx 150\frac{\mathrm{Mbit}}{\mathrm{s}}\)

Latency: DSL: \(\approx 100\mathrm{ms}\) Airplane: \(>7\mathrm{hr}\)

For fun, let's try something a little bigger on both sides: OC-768 vs Boeing 747-400F plane filled with \(2\mathrm{TB}\) hard drives.

Bandwidth: OC-768: \(38\frac{\mathrm{Gbit}}{\mathrm{s}}\) 747-400F: \(\frac{250000\mathrm{lb}}{7\mathrm{hr}} \times \frac{2\mathrm{TB}}{1.7\mathrm{lb}} \times \frac{1\mathrm{hr}}{60\mathrm{min}} \times \frac{1\mathrm{min}}{60\mathrm{s}} \times \frac{8\mathrm{Tbit}}{1\mathrm{TB}} \approx 93\frac{\mathrm{Tbit}}{\mathrm{s}}\)

Latency: OC-768: \(<100\mathrm{ms}\) 747-400F: \(>7\mathrm{hr}\)

Clearly, hard drives on an airplane will win in a purely bandwidth driven application but airplanes suffer from incredibly high latency. You will have to decide which is best choice based on your particular use scenario.