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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
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]
4
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]
5
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]
6
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]
7
Vehicles on Highways Networks
Source Destination
[M. Ammar, Co-Next 2005]
Vehicles on Highways Networks
Source Destination
[M. Ammar, Co-Next 2005]
8
Vehicles on Highways Networks
Source Destination
[M. Ammar, Co-Next 2005]
DakNet (Pentland, Fletcher, and Hasson)
[M. Ammar, Co-Next 2005]
9
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]
10
Epidemic Routing – The Idea
[M. Ammar, Co-Next 2005]
Epidemic Routing – The Idea
[M. Ammar, Co-Next 2005]
11
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
12
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
13
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
Model of node mobility
IMEP IMEP IMEP IMEP IMEP
ERA ERA ERA ERA ERA
Internet MANET Encapsulation Protocol
Epidemic Routing Agent
Epidemic Routing – Evaluation
[Vahdat & Becker, TechReport 2000]
14
Epidemic Routing – Evaluation
[Vahdat & Becker, TechReport 200]
Epidemic Routing – Evaluation
[Vahdat & Becker, TechReport 2000]
15
Epidemic Routing – Evaluation
[Vahdat & Becker, TechReport 2000]
Epidemic Routing – Evaluation
[Vahdat & Becker, TechReport 2000]
16
The Trouble with ER
• Potentially high-failure rate • Message duplication consumes nodal
resources • Some mobility patterns can cause
disconnection • Can be improved with contact probability
information - Levine et al
[M. Ammar, Co-Next 2005]
Message Ferrying (MF) @ GT
• Zhao and Ammar • Exploit non-randomness in device
movement to deliver data – A set of nodes called ferries responsible for
carrying data for all nodes in the network – Store-carry-forward paradigm to
accommodate disconnections • Ferries act as a moving communication
infrastructure for the network
[M. Ammar, Co-Next 2005]
17
Message Ferrying – The Idea
D
MF
M
S
MF
S M
D
[M. Ammar, Co-Next 2005]
MF Variations
• Ferry Mobility – Task-oriented, e.g., bus movement – Messaging-oriented, e.g., robot movement
• Regular Node Mobility – Stationary – Mobile: task-oriented or messaging-oriented
• Number of ferries and level of coordination • Level of regular node coordination • Ferry designation
– Switching roles as ferry or regular node [M. Ammar, Co-Next 2005]
18
MF for Networks with Mobile Nodes
• Nodes are mobile and limited in resources, e.g., buffer, energy
• Single ferry is used – Not limited in buffer or energy – Trajectory of the ferry is known to all nodes
• Data communication in messages – Application layer data unit – Message timeout
[M. Ammar, Co-Next 2005]
Four Approaches • Non-Proactive ( = Messaging-Specific) mobility
– Ferrying without Epidemic Routing – Ferrying with Epidemic Routing
• Proactive Routing Schemes – Node-Initiated MF(NIMF)
• Nodes move to meet ferry – Ferry-Initiated MF (FIMF)
• Ferry moves to meet nodes
[M. Ammar, Co-Next 2005]
19
Node-Initiated Message Ferrying
Meet the
ferry? OK
Working
If no, keep working
[M. Ammar, Co-Next 2005]
Node-Initiated Message Ferrying
Go to Ferry
[M. Ammar, Co-Next 2005]
20
Node-Initiated Message Ferrying
Send/Recv
Go to Work
[M. Ammar, Co-Next 2005]
Node-Initiated Message Ferrying
Go to Work
[M. Ammar, Co-Next 2005]
21
Intentional
Not planned
Mode Transition
WORKING GO TO FERRY
GO TO WORK SEND/RECEIVE
detour: whether the node is detouring; mode: which mode the node is in; 1. WORKING mode
detour = FALSE; IF Trajectory Control indicates time to go to the ferry,
detour = TRUE; mode = GO TO FERRY;
On reception of a Hello message from the ferry: mode = SEND/RECV;
2. GO TO FERRY mode Calculate a shortest path to meet the ferry; Move toward the ferry; On reception of a Hello message from the ferry:
mode = SEND/RECV; 3. SEND/RECV mode
Exchange messages with the ferry; On finish of message exchange or the ferry is out of range:
IF detour is TRUE, mode = GO TO WORK; ELSE mode = WORKING;
4. GO TO WORK mode Move back to node’s location prior to the detour; On return to the prior location:
mode = WORKING; On reception of a Hello message from the ferry: mode = SEND/RECV;
Node Operation in NIMF
[Zhao et al., MobiHoc04]
22
Ferry Operations in NIMF
1. Move according to a ferry route; 2. Broadcast Hello messages periodically; 3. On reception of an Echo message from a
node: Exchange messages with the node;
[Zhao et al., MobiHoc04]
Node Trajectory Control
• Whether node should move to meet the ferry • Goal: minimize message drops and reduce
proactive movement • Go to ferry if
– Work-time percentage > threshold – and – Estimated message drop percentage > threshold
[M. Ammar, Co-Next 2005]
23
Simulations
• Ns simulations using 802.11 MAC and default energy model
• 40 nodes in 5km x 5km area • 25 random (source, destination) pairs • Node mobility
– random-waypoint with max speed 5m/s • Message timeout: 8000 sec • Single ferry with speed 15m/s
– Rectangle ferry route [M. Ammar, Co-Next 2005]
Performance Metrics
• Message delivery rate • Message Delay • Number of delivered messages per unit
energy – Only count transmission energy in regular
nodes
[M. Ammar, Co-Next 2005]
24
Message Delivery Rate
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
100 200 300 400 500 600 700 800
Mes
sage
delivery rate
Node buffer s ize (mes s ages )
E pidemic R outingE pidemic R outing (w/ ferry)
NIMFFIMF-‐NNFIMF-‐T A
FIMF
NIMF
F w/ER
ER
[M. Ammar, Co-Next 2005]
Message Delay
0
500
1000
1500
2000
2500
3000
3500
4000
100 200 300 400 500 600 700 800
Mes
sage
delay
(sec
)
Node buffer s ize (mes s ages )
E pidemic R outingE pidemic R outing (w/ ferry)
NIMFFIMF-‐NNFIMF-‐T A
FIMF
F w/ER
ER
NIMF
[M. Ammar, Co-Next 2005]
25
Impact of Node Mobility Pattern
Mobility Model Scheme Delivery Rate Delay (sec) Energy efficiency (KB/J) Random
Waypoint NIMF 0.912 3569 300 FIMF 0.931 3691 181
ER(w/ ferry) 0.661 2084 14 ER 0.316 1546 10
Limited Random
Waypoint NIMF 0.699 3896 267 FIMF 0.850 4091 137
ER(w/ ferry) 0.211 2851 11 ER 0.061 2221 6
[M. Ammar, Co-Next 2005]
Where Does MF Fit?
• Consider the space of wireless mobile networks
• Two Important Dimensions – Relative Mobility – Density
[M. Ammar, Co-Next 2005]
26
Some Terminology • A Space Path: A multi-hop path where all the
links are active at the same time
• A Space/Time Path: A multi-hop path that exists over time
• NOTE: S path is a special case of S/T path • See http://www.cc.gatech.edu/fac/Mostafa.Ammar/papers/STroute.ps
[M. Ammar, Co-Next 2005]
Example
A Space Paths Network
[M. Ammar, Co-Next 2005]
27
Example
A No Path Network
[M. Ammar, Co-Next 2005]
Example
A Space Time Path
[M. Ammar, Co-Next 2005]
28
Example
A Hybrid Network
[M. Ammar, Co-Next 2005]
The Mobile Wireless Space
Node Density
“ Relat
ive M
obility
”
High
Low
High
Space Paths
Low
No (Space/Time) Paths
Space/Time Paths
Hybrid Environments
[M. Ammar, Co-Next 2005]
29
Mapping Solutions to Space
Node Density
“ Mob
ility
”
High
Low
Low
High
Space Paths
No (Space/Time) Paths
Space/Time Paths
Hybrid Environments
MF is necessary here
Traditional MANET solutions apply here
MF is applicable for the entire space
[M. Ammar, Co-Next 2005]
MAC Layer Support for Delay Tolerant Video Transport in
Disruptive MANETs Morten Lindeberg, Stein Kristiansen, Vera Goebel and omas Plagemann
University of Oslo, Department of Informatics [mglindeb, steikr, goebel, plageman]@i".uio.no
30
Background and Motivation
• Emergency and rescue scenarios • Video streaming services can improve
communication and operational efforts – E.g., firemen wearing head-mounted cameras
• Infrastructure destroyed or not existing
• Solution: Mobile ad hoc networks with possible disruptions
59
Target Scenario
CCCCCCCr2Cr1
I5I4
Cr1
I5I4
I3I3
I2
I
I1
I2
I1Sr
Ix - Intermediate node(s)Sr - Source node
Crx- Carrier node(s)CCC - Command Control Center
Location of the accident
500 m
500
m
Command and control center
Distance=1750 m
• Mimic realistic scenario • Enforce store-carry-forwarding
60
31
Use existing technology? • Video encoding:
– H.264 significantly reduce bandwidth requirements • Transport:
– TCP does not work well
• Network: – IP + MANET routing: OLSR
• Wireless: – IEEE 802.11 ad hoc mode
61
Transport: Overlay Solution
• 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)
62
32
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
63
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)
– Reduce non-meaningful re-transmissions (MAC re-transmission limit)
64
33
Implementation • Implemented in ns-3 (network simulator)
• Workload: – Foreman CIF resolution (352x288) – 12 second duration on repeat – H.264 baseline profile – Target bitrate 256 kb/s
• Wireless model: – IEEE 802.11b ad hoc mode – DSSS modulation – Friis propagation loss model – Constant speed propagation delay model
65
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)
66
34
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 %
67
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
68
35
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%
69
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
70
36
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
71
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
72