1. BITS Pilani
Hyderabad Campus
A Survey of Social Based
Routing in Delay Tolerant
Networks: Positive and
Negative Social Effects
Abhishek Thakur
CSIS,
BITS-Pilani, Hyderabad Campus

2. 10/12/2013 Slide 2 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
For links that are intermittent or poor in quality, end-to-end
connectivity and routing may not be guaranteed especially in
Extreme Scenario.
Limits of MANets and Connected
Networks
Prob success (iid fail prob pf) over k links:
For E2E delivery must have all links up
But, expected # of failed links is
k
fsfs pkppp )1()(;1
fkp

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Probability of Delivery

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Optimizations on classic ad-hoc and delay-tolerant networking
algorithms and began to examine factors such as
security, reliability, verifiability
– Node mobility would be exploited to help deliver message (mobility-assisted or store-carry-
and-forward)
Delay-Tolerant Networking Architecture
– http://tools.ietf.org/html/rfc4838
Bundle Protocol Specification
– http://tools.ietf.org/html/rfc5050
Why? What?

5. 10/12/2013 Slide 5 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Deep Space Communications
– Beyond near-earth
– Landers, Orbiters, Deep Space Probes
Sensor Networks
– Terrestrial: Ocean or Land Based
– Extra-terrestrial objects (on planets, etc)
High-Stress Physical Environments
– Battlefield, Civil Emergency, Submarines
This and next few slides – ref Kevin Fall - 2008
What is Extreme?

6. 10/12/2013 Slide 6 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
• Large Delays
• Intermittent and Scheduled Links
• Bandwidth Asymmetry
• Limited Power
• Limited Emission Requirements (LPI/LPD)
• Heterogeneous Network Architectures
• Link Security Needs
• Very Large Scale (e.g. sensor nets)
Communications Challenges

7. 10/12/2013 Slide 7 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Unusual Devices

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Extreme systems
• Do not (won’t) run IP
– High overhead, for global routing
– Intra-Oceans: investigate routing
– Space: very limited routing [e.g. rover
to lander]
– Sensors: novel or simple routing, low
power
• Domain-specific features:
– Naming, delivery abstraction, QoS
But we don’t want to scrap
existing (Internet) software
and experience
Heterogeneous Architectures
The NASA Deep Space
Network (DSN)
– 3 70m-antenna array [USA, Spain,
Australia]
Underwater Acoustic Modems
– Bottom-to-top comm under 20kbps to
6Km
Low-Power CMOS Radios
– Conventional and (hopefully) UWB
SINGCARS and EPLRS
Military Radios

9. 10/12/2013 Slide 9 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Goals of the DTN architecture:
– Interoperability across network architectures
– Reliability robust to link and node failure
Components:
– Reliable Message Overlay with Routing
– Interoperability Gateways
– Flexible Naming Scheme
– Per-hop Authentication with CoS
Delay-Tolerant Network
Architecture

10. 10/12/2013 Slide 10 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
End-to-End Message Service: “Bundles”
– “postal-like” delivery over regional transports
– Optional class of service/notification
Key Idea: Custody Transfer
– Custodian owns reliable-delivery guarantee
– Bundles transferred between custodians toward
destination
– Sender may free resources upon successful custody
transfer
Reliable Message Overlay

11. 10/12/2013 Slide 11 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
“Classic” Concepts (Internet):
– Routing: selecting best next hop for every possible
destination
– Forwarding: sending packet to best next hop
• Typically, “on demand” [statistical multiplexing]
• Forwarders know a-priori next hop for every destination
DTN Concepts:
– Routing: selecting best DTN next hop for destination
– Forwarding: sending a bundle p2p when possible
– Custody Transfer: reliable intra-DTN delivery (with storage)
Routing, Forwarding and
Custody Transfer

12. 10/12/2013 Slide 12 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Bundle Routing Example
A
B
B
Intermittent Links
DS
B
B
B
End-to-end Acknowledgement
(Sent using bundles, path omitted for clarity)
Contact Schedule
Aircraft
HUMMV
Schedule
Aircraft
HUMMV

13. 10/12/2013 Slide 13 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Is it possible that data can be delivered?
– path between a source and a destination maybe
always won’t exist
Solution
– Traditional protocols: Internet (RIP, OSPF); Ad hoc
(DSR, AODV) would fail
– Formerly, mobility viewed as evil; Now, it’s perfect
– Node mobility would be exploited to help deliver message
(mobility-assisted or store-carry-and-forward)
Mobility-assisted routing

14. 10/12/2013 Slide 14 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Two categories
– auxiliary nodes assisted (ANA) routing
• a set of special auxiliary nodes needed to assist data delivery
• VANETs etc.
• Throw-boxes / Ferry / Courier nodes / Autonomous Agents …
– independent mobile nodes (IMN) routing
• there is no additional participants in the deployment area
• message delivery achieved by node’s inherent movement
• Proactive & reactive
• Flooding vs. Heuristics based
Overview of Routing schemes

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Pure Flooding
Probabilistic Flooding
Utility Based Flooding – goes into Heuristics
Multiple copies get created; Delivery reports used to clean them up
Epidemic: Flooding-based

16. 10/12/2013 Slide 16 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
tX(Y): time since X last saw Y
Indirect location information
 diffused with node mobility
smaller timer closer distance
 For most mobility models
Utility-based Routing
A
D
B
tB(D) = 100
t(D) = 0
t(D) = 26
t(D) = 68
tA(D) = 138
t(D) = 218
Last encounter timers
D D
Utility UX(Y) = f(tX(Y))
Policy: forward to B if
UB(D) > UA(D) + Uth
(A. Lindgren et al. ‘03)

17. 10/12/2013 Slide 17 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Other knowledge-based routing
– MaxProp: A variation of Dijkstra’s algorithm
• Link weight: an estimate of delivery likelihood between two nodes
– MobySpace: each node maintains a high-dimension Euclidean
space
• Euclidean space: to describe mobility pattern of each node
• Encounter occurred: handover message only if the encountered node
has more similar mobility pattern with the destination.

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Performance metric
– Message delivery ratio
• The fraction of generated messages that are correctly delivered to
the final destination within a given time period
– Transmission delay
• The time from a message is generated through it is received by
destination
– Number of transmissions (copies)
• The number of message exchange occurred between two nodes
Routing objective

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The performance of 2-hop scheme is close enough to multi-hop
scheme (Burns et al, ’05)
Spray and wait scheme
– 2-hop relay scheme
• “Spray” a number of copies to the network, then “wait” until one of relay
nodes meets the desination
– Limited number of copies to L
• Multi-path diversity to reduce delay
• Achieves O(1) per node capacity
2-hop relay (multiple copies)

20. 10/12/2013 Slide 20 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
source starts with L copies
whenever a node with L > 1 copies finds a new node, it hands over half of the copies (L/2)
that it carries; Until L = 1
Binary Tree-based Spraying
Src
C
B
Dst
D
E
F
D
D
D
DL = 4
L = 2
L = 2
L = 1
L = 1
L = 1
L = 1

21. 10/12/2013 Slide 21 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Routing issue in DTN is challenge, attracting more attention
Category of routing scheme
Have good scalability of DTN by exploring node mobility
Future direction: develop more realistic networks; from military to public
application
– Vehicle-based networks
– Pocket-switched networks
– Social networks
– Wildlife tracking networks
Summary
ANA scheme IMN scheme
Knowledge-basedFlooding-based
Routing schemes

22. 10/12/2013 Slide 22 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
• DTN Intro
• Node Mobility vs. User’s Social Relations and Behavior
• Positive Social Characteristics
• Negative Social Characteristics
Brief Information From Paper

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Community Detection
• Modularity, Network of Communities
Information Propagation
• Spread factor, Spreading Time
• Connection Density, Influencing Factor, Critical Nodes
Recommendation System(s)
• Online shopping / reviews, Twitter / RSS ranking etc.
Security and Privacy
• Anti-Spam, limitations of blacklists, multiparty Authorization.
• Privacy / Anonymity and re-identification algo for anonymized social
network
Social Network Analysis

24. 10/12/2013 Slide 24 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Custody Transfers tied to contact graphs and duration of contact
Communality, Centrality and Similarity of nodes
Time slot based graph vs. Each edge records number, time and
period of encounters
Contact graphs for DTN nodes and Social graphs for owners
are loosely identical.
Question: How do the encounter tables get shared on large
DTNs? Possibly scope to research further.
Social property if DTN : Graphs

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Since DTN nodes are carried by people, they will tend to mimic
communities. {impact of device sharing}
Sociological Centrality metrics will imply that such nodes are
strong relay nodes
• Degree, Betweenness & Closeness to Destination
Similarity to Destination User location, Destination User
Interests etc. implies that such relay nodes are likely to get
near the destination. {challenge other than location how to
capture and model similarity – data generated, apps used
etc.}
Social property if DTN :
Community, Centrality, Similarity

26. 10/12/2013 Slide 26 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Similarity can infer Friendship: Long lasting regular contacts
coupled with common interests in real world.
Rational Selfish behavior of social nodes implies that they want
to send/receive DTN data not act as relay’s for other’s data
… Friendship and Selfishness

27. 10/12/2013 Slide 27 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
Label Routing Hui & CrowCroft – Pocket Switched nodes –
IEEE PerCom 2007
• Community included as part of label
• Nodes also share their affiliations and Groups i.e. Social
communities
SimBet Routing Daly and Haar (ACM Symposium … 2007)
• Explores bridge nodes using betweenness, centrality and
similarity.
• Using Betweenness and Similarity to destination, the Utility
of node as next hop can be evaluated
• Scales by estimating centrality using only locally visible
information – but can have –ve effects
Approaches used for Benefiting
from Social Characteristics

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Bubble Rap Forwarding Hui & other (MobiHoc 2008)
• Community and centrality
• Fast transfer towards destination community – bubble up
towards global centrality and bubble within community
• Changeless to in Hierarchical communities or for
communities on periphery (non-central)
Social Multicasting Gao & others (MobiHoc 2009)
• Centrality metric and community metric for relay
• Single data or multi-data multicast
• For Single data, assumed uniform destination distribution
• For Muti-data – use gateway nodes for multiple communities
Approaches used for Benefiting
from Social Characteristics…

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Homophily Based data diffusion Zang & others (MobiHoc
2009)
• Prioritizes data propagation order (contact duration / storage
space limited)
• Homophily => shared interest {challenge to identify / model this}
• Share most similar data items between friends and most
different Data Items between strangers
Social Multicasting Bulut & others (GLOBECOM 2010)
• Social Pressure Metric [weighted by frequent long lasting regular contacts]
• Data sharing / storage complexity is high
User Centric Disseminataion Gao & Cao (INFOCOMM 2011)
Approaches used for Benefiting
from Social Characteristics…

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Questions ?
Thanks

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Backup

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http://www.dtnrg.org
http://irtf.org/dtnrg
http://www.nasa.gov/mission_pages/station/research/experimen
ts/DTN.html
– Disruption Tolerant Networking
Slide references
– http://bwrc.eecs.berkeley.edu/php/pubs/pubs.php/762/Delay%20Tolerant%20Architectur
e%20v1%20Kevin%20Fall.ppt
– http://www.networks.howard.edu/hguo/docs/prest05.ppt
– http://netlab.cs.ucla.edu/wiki/files/relaycast_icnp08_final.ppt
Additional References

33. 10/12/2013 Slide 33 NetClique.in Internal Presentations BITS Pilani, Hyderabad Campus
• Bundle, Payload, Fragment
• Bundle node
• Bundle protocol agent
• Convergence layer adapters
• Application agent
• Bundle endpoint
• Forwarding, Registration, Delivery
• Deliverability/Abandonment
• Deletion, Discard
• Transmission
• Custody
Terminology