dtn

Overview ¶

Example: Store and forward for deep space

Everything else in these examples assumes the link is up. On a deep space mission it usually is not: a relay is behind the planet, a station is scheduled for someone else, or the round trip is forty minutes and a handshake finishes tomorrow.

Delay-Tolerant Networking is the answer, and it is two layers:

Bundle Protocol (CCSDS 734.2, pkg/bp)
  The network layer. A bundle is addressed, prioritised and given a
  lifetime, then stored at each hop rather than held in an end-to-end
  session.

Licklider Transmission Protocol (CCSDS 734.1, pkg/ltp)
  The convergence layer for one hop. It pushes a whole block, then asks
  what was missed. No handshake, because a handshake costs a round trip.

This example builds a bundle, sends it over LTP across a link that loses a segment, recovers it, and reads the bundle out the other side. Then it fragments a bundle for a contact window too short to fit it.