Delay Tolerant Networks

Roland Cheng

April 24, 2007 Mobile Communication 2

PAN ~1m

LAN ~100 m

MAN ~10 km

WAN ~1,000 km

Internet ~10,000 km

Inter-planetary Communication ~100×106 km

April 24, 2007 Mobile Communication 3

Outline

Review Internet protocol stack

• Internet vs. Delay Tolerant Networks

• Lagrange point relays

• Summary

April 24, 2007 Mobile Communication 4

5 Layer TCP/IP Model

Application Layer http, ssh, pop3

Transport Layer TCP, UDP

Network Layer IP

Data Link Layer 802.11

Physical Layer MPSK, MQAM

April 24, 2007 Mobile Communication 5

Outline

• Review Internet protocol stackInternet vs. Delay Tolerant Networks

• Lagrange point relays

• Summary

April 24, 2007 Mobile Communication 6

Assumptions in TCP/IP

• Small propagation latencies

• High data rates

• Bidirectional, symmetric channels

• Continuous connectivity

A B

April 24, 2007 Mobile Communication 7

Assumptions in DTN

• Large propagation delays

• Low data rates

• Asymmetric channels

• Intermittent connectivity

April 24, 2007 Mobile Communication 8

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, 2007 Mobile Communication 9

Data Flow Example in DTN

April 24, 2007 Mobile Communication 10

Outline

• Review Internet protocol stack

• Internet vs. Delay Tolerant NetworksLagrange point relays

• Summary

April 24, 2007 Mobile Communication 11

Lagrange Point Relays

Sun Earth

April 24, 2007 Mobile Communication 12

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, 2007 Mobile Communication 13

Outline

• Review Internet protocol stack

• Internet vs. Delay Tolerant Networks

• Lagrange point relaysSummary

April 24, 2007 Mobile Communication 14

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