Delay Tolerant Networks Roland Cheng

April 24, 2007Mobile Communication2 PAN ~1m LAN ~100 m MAN ~10 km WAN ~1,000 km Internet ~10,000 km Inter-planetary Communication ~100×10 6 km

April 24, 2007Mobile Communication3 Outline  Review Internet protocol stack Internet vs. Delay Tolerant Networks Lagrange point relays Summary

April 24, 2007Mobile Communication4 5 Layer TCP/IP Model Application Layerhttp, ssh, pop3 Transport LayerTCP, UDP Network LayerIP Data Link Layer Physical LayerMPSK, MQAM

April 24, 2007Mobile Communication5 Outline Review Internet protocol stack  Internet vs. Delay Tolerant Networks Lagrange point relays Summary

April 24, 2007Mobile Communication6 Assumptions in TCP/IP Small propagation latencies High data rates Bidirectional, symmetric channels Continuous connectivity AB

April 24, 2007Mobile Communication7 Assumptions in DTN Large propagation delays Low data rates Asymmetric channels Intermittent connectivity

April 24, 2007Mobile Communication8 Bundling Protocol Place another layer between application and transport layer Bundling protocol (CFDP) –Keeps all data and meta data needed to transmit a packet until receive ACK (store-and -forwarding) –Transmits data optimistically –Routing of packets should take advantage of scheduled outage –Uses new ARQ algorithms that can handle long delays

April 24, 2007Mobile Communication9 Data Flow Example in DTN

April 24, 2007Mobile Communication10 Outline Review Internet protocol stack Internet vs. Delay Tolerant Networks  Lagrange point relays Summary

April 24, 2007Mobile Communication11 Lagrange Point Relays SunEarth

April 24, 2007Mobile Communication12 Lagrange Point Relays A Lagrange point is a solution to the restricted 3-body problem –a small object at a Lagrange point will remain stationary relative to two large, orbiting masses, assuming only gravitational effects Placing a relay station at L4 and L5 will provide alternative signal paths when no line-of-sight

April 24, 2007Mobile Communication13 Outline Review Internet protocol stack Internet vs. Delay Tolerant Networks Lagrange point relays  Summary

April 24, 2007Mobile Communication14 Summary TCP/IP is not suitable for interplanetary communication –Large propagation delays, intermittent connectivity Bundling protocol extends the network stack by providing asynchronous store- and-forwarding service Lagrange point relays can alleviate LOS occlusions