Some systems may have to be designed around interruptions rather than around a steady connection. A recent NASA test offers one example.

Rethinking Network Assumptions

NASA has successfully tested the first deep space communications network modeled on the Internet. Engineers from NASA's Jet Propulsion Laboratory in Pasadena, Calif., used software called Disruption-Tolerant Networking, or DTN, to transmit dozens of space images. NASA and Vint Cerf, a vice president at Google Inc., in Mountain View, Calif., partnered 10 years ago to develop this software protocol.

Building for Breaks

The release set out the difference from the familiar internet: unlike TCP/IP on Earth, the DTN does not assume a continuous end-to-end connection. It said that in its design, if a destination path cannot be found, the data packets are not discarded. Instead, each network node keeps the information as long as necessary until it can communicate safely with another node.

One way to read this is that reliability can mean different things. A design that lets each step hold on to what it has may value eventual delivery over speed. For anyone building a project that depends on links they do not control, it may be worth asking what each part should do while it waits.

Harsh conditions can prompt a fresh look at what makes a system sturdy. Perhaps resilience depends less on keeping every connection open than on planning for the moments when one closes.

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