View
216
Download
0
Tags:
Embed Size (px)
Citation preview
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