Delay Tolerant Networks

Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space.
   — Douglas Adams, HHGTTG

One way to get an idea of what’s in store for the internet is to peek over the technical horizon by reading the Internet Drafts put out by the Internet Engineering Task Force (IETF) and the Internet Research Task Force (IRTF).

One interesting current research area is that for Delay Tolerant Networks (DTNs); networks where the conventional TCP/IP assumptions of continuous connectivity and “low” delay are broken. One of the things this translates into is standards for an Interplanetary Internet, but it also has relevance for sensor networks, communications with submarines and web access for reindeer herders.

[2018-03-05: Updated with new URLs, some via the Wayback Machine. The reference to the main Internet-Draft has become a reference to the superseding RFC.]

If you are interested in this area, the best place to start is probably the DTN Research Group’s web site. This references the latest versions of the relevant Internet-Draft documents as well as many others, and has a collection of links to other relevant sites.

In terms of interesting documents to read, the starting point has to be the current version of the Delay-Tolerant Network Architecture Internet-Draft by Cerf et al. The Bundle Protocol Specification document is probably not a must-read unless you are planning to launch a satellite soon, but the Example Interplanetary Internet Bundle Transfer gives a walkthrough of how the system might work in practice. A single paragraph from the latter gives a flavour of the kind of practical concerns involved:

Note that any bundles sent by GW3 after 1156 GW1 time cannot be acknowledged before the next contact, because the bundle will arrive at GW1 after the end of GW1’s transmission time (1200). Since the next contact between GW1 and GW3 might be the subsequent Monday, the acknowledgement delay might be VERY long. Bundles sent by GW4 after 1358 cannot be acknowledged during the current contact, because they will not be received before GW1’s transmission time ends at 1430.

The web site also includes a prototype C implementation of the architecture.