1 Delay Tolerant Networking Thomas Plagemann Distributed Multimedia Systems Group Department of Informatics University of Oslo Outline • Background, motivation, overview • Epidemic routing • Message ferrying • Mobility/density space • Acknowledgement: Many transparencies are from Mustafar Ammar’s keynote talk at Co-Next 2005
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Delay Tolerant Networking - Universitetet i oslo · Transport: Overlay Solution • A delay tolerant overlay – Store-carry-forward paradigm – Dts-Overlay – Inspired by MOMENTUM
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Delay Tolerant Networking
Thomas Plagemann Distributed Multimedia Systems Group
Department of Informatics University of Oslo
Outline
• Background, motivation, overview • Epidemic routing • Message ferrying • Mobility/density space • Acknowledgement: Many transparencies
are from Mustafar Ammar’s keynote talk at Co-Next 2005
2
Traditional Wired Networks
• separation between endsystems and routers • routers responsible for finding stable path
router
endsystem (source) endsystem
(destination)
[M. Ammar, Co-Next 2005]
“Traditional” Mobile Ad-hoc Wireless Networks (MANET)
• no separation between endsystems and routers • nodes responsible for finding stable path
node (destination)
node = endsystem + router
node (source)
[M. Ammar, Co-Next 2005]
3
“Traditional” Mobile Ad-hoc Wireless Networks (MANET)
• nodes may move • routing layer responsible for reconstructing (repairing)
stable paths when movement occurs
node (destination)
node (source)
[M. Ammar, Co-Next 2005]
The “Traditional” MANET Wireless Paradigm
• The Network is “Connected” – There exists a (possibly multi-hop) path from
any source to any destination – The path exists for a long-enough period of
time to allow meaningful communication – If the path is disrupted it can be repaired in
short order – “Looks like the Internet” above the network
layer
[M. Ammar, Co-Next 2005]
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The Rise of Sparse Disconnected Networks
[M. Ammar, Co-Next 2005]
Sparse Wireless Networks
• Disconnected – By Necessity – By Design (e.g. for power considerations)
• Mobile – With enough mobility to allow for some
connectivity over time – Data paths may not exist at any one point in
time but do exist over time
[M. Ammar, Co-Next 2005]
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Mobility-Assisted Data Delivery: A New Communication Paradigm
• Mobility used for connectivity • New Forwarding Paradigm Store Carry for a while forward • Special nodes: Transport entities that are not
sources or destinations
[M. Ammar, Co-Next 2005]
Data Applications
• Nicely suitable for Message-Switching • Delay tolerance … but can work at
multiple time scale (a.k.a. Delay Tolerant Networks )
[M. Ammar, Co-Next 2005]
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Some Delay-Tolerant Systems
• ZebraNet and SWIM • Data MULE and Smart-Tags • Vehicle-to-Vehicle Communication • DakNet • Epidemic Routing • Message Ferrying
[M. Ammar, Co-Next 2005]
SWIM
[M. Ammar, Co-Next 2005]
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Vehicles on Highways Networks
Source Destination
[M. Ammar, Co-Next 2005]
Vehicles on Highways Networks
Source Destination
[M. Ammar, Co-Next 2005]
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Vehicles on Highways Networks
Source Destination
[M. Ammar, Co-Next 2005]
DakNet (Pentland, Fletcher, and Hasson)
[M. Ammar, Co-Next 2005]
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Epidemic Routing
• Vahdat and Becker • Utilize physical motion of devices to transport
data • Store-carry-forward paradigm
– Nodes buffer and carry data when disconnected – Nodes exchange data when met – data is replicated throughout the network
• Robust to disconnections • Scalability and resource usage problems
[M. Ammar, Co-Next 2005]
Epidemic Routing – The Idea
[M. Ammar, Co-Next 2005]
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Epidemic Routing – The Idea
[M. Ammar, Co-Next 2005]
Epidemic Routing – The Idea
[M. Ammar, Co-Next 2005]
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Epidemic Routing – The Idea
message is delivered…
[M. Ammar, Co-Next 2005]
Epidemic Routing – Basic Elements
• Each node contains – Message buffer – Hash table – Summary vector – List of last seen nodes
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Epidemic Routing – The Protocol
[Vahdat & Becker, TechReport 200]
Epidemic Routing – Multiple Hops
• Each message contains: – Unique message ID – Hop count – Ack request (optional)
• Tradeoff buffer size vs. message delivery
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Epidemic Routing – Evaluation • Implementation in ns-2
– 50 mobile nodes – Area 1500m x 300m – Random waypoint – Speed 0 – 20 m/s (uniformly distributed) – Message size 1 KB – 45 message sources/sinks (each sends one message to the
others) – Each second 1 message
IEEE 802.11 MAC protocol Model of radio propagation
• A delay tolerant overlay – Store-carry-forward paradigm – Dts-Overlay – Inspired by MOMENTUM [1] – Messages are sent hop-by-hop – Route through carrier nodes when no route exist
• Problem: packet loss
Dts-Overlay
UDP
IP / OLSR
MAC(IEEE 802.11 a/b)
Route availability
+MAC address/ARP status
Rejectedpackets
+Retransmission
queue status
PHY(IEEE 802.11 a/b)
Dts-Overlay
UDP
IP / OLSR
MAC(IEEE 802.11 a/b)
PHY(IEEE 802.11 a/b)
<OverlayMessage>
Node 1 Node 2
[1] Cabrero, S., Paneda, X.G., Plagemann, T., Goebel, V.: Overlay solution for multimedia data over sparse MANETs. In: International Wireless Communications and Mobile Computing Conference, IWCMC (2009)
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Packet loss • OLSR routes with broken links
– In essence, lower layers are not delay tolerant
• Address Resolution Protocol (ARP) 1. ARP will loose packets if no nodes reply with
matching MAC address to the broadcasted IP address
• IEEE MAC 802.11
1. Packets silently dropped after final retransmission 2. .. or if queue exceeds limit
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Solution • ARP Support:
– Avoid packet loss by only forwarding when address is resolved
• MAC Support (IEEE 802.11b):
– MAC Return: Do not drop packet after final re-transmission, hand it to Dts-Overlay
– Link Adapt: Do not forward if the MAC transmission queue is filling (link is probably down)
• Wireless model: – IEEE 802.11b ad hoc mode – DSSS modulation – Friis propagation loss model – Constant speed propagation delay model
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Evaluation • Metrics:
1. Packet reception (Rxv) 2. Buffered packets (Buf ) 3. Packet loss (Pl) 4. Sum of bytes (video) at PHY layer (Txtot)
• Present average from five different runs 3600 s duration • Main-Studies (3600 s duration):
– ER (custom scenario) – Sparse MANET (1250 m x 1250 m, 20 nodes, random walk) – Dense MANET (250 m x 250, 20 nodes and additional workload,
random walk)
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Results: Pre-Study
• Address Resolution
– Affect packet loss substantially! – We achieve lowest packet loss with Dynamic
ARP! – .. wait for ARP resolution before using a link
Default Static Dynamic Pl 39.3 % 31.7 % 19.5 %
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Configurations
C3 C4 C5 C6 C7 Re-trans. 7 3 3 3 3 MAC Return
No No No Yes Yes
Link Adapt No No Yes No Yes
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Results: ER
0 %
10 %
20 %
30 %
40 %
50 %
60 %
70 %
80 %
90 %
100 %
C3 C4 C5 C6 C7
Pl Buf Rx
Lowering retransmission limit cause packet loss
Deploying Link Adapt does not affect packet
reception much
MAC Return close to eliminates all
packet loss
Link Adapts improves further,
even reduces total transmission ov by
4%
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Results: Sparse MANET Tendencies are the same, high standard deviation (mobility)
Switch to single run
0
20000
40000
60000
80000
100000
120000
140000
160000
0 500 1000 1500 2000 2500 3000 3500
Pack
et co
unt (
#)
Time (s)
SentC3C4C5C6C7
0
100
200
300
400
500
600
700
800
900
0 500 1000 1500 2000 2500 3000 3500
Txt (
MB)
Time (s)
C3C4C5C6C7MAC Return
improves reception
With even less transmissions than default configuration
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Results: Dense MANET
0 20 40 60 80
100 120 140 160
C3 C4 C5 C6 C7
TxTot (MB)
TxTot (MB)
Not much loss really, although some duplicates for MAC Return
Link Adapt has strong effect on transmissions
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Conclusion
• MAC Support Evaluation: – MAC Return drastically reduce packet loss – Allow us to lowering MAC retransmission limit – Link Adapt lowers overhead of transmissions
that are not meaningful • Usability is strengthened through
evaluation also in a dense MANET
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Summary
• Background, motivation, overview • Epidemic routing • Message ferrying • Mobility/density space • Acknowledgement: Many transparencies
are from Mustafar Ammar’s keynote talk at Co-Next 2005