The increasing number of personal devices with wireless communication capabilities makes it possible the creation of spontaneous networks in which devices communicate occasionally depending on contact opportunities. This intermittent communication may be due to mobility and power-limitations of devices, physical obstacles and distance, resulting in the possible nonexistence of end-to-end paths toward a destination. In summary, spontaneous networks are characterized by being highly dynamic, composed of mobile and static nodes that are able to take advantage of opportunistic time-varying contacts. This tutorial aims to give an introduction to the challenges and research issues behind the development of opportunistic networking solutions able to boost the deployment of spontaneous networks. Special attention will be given to the fundamental building block: routing over opportunistic networks. Since the effciency of spontaneous networks depends upon the way contacts occur between carriers of communication devices, special attention will also be given to the analysis of method to detect social structures based on opportunistic contacts. To emphasize the impact that opportunistic networking technology may have, this tutorial ends up with the description of major aspects of future forwarding schemes: interest-based and information-centric forwardings. This presentation was given as a tutorial in the IEEE 3rd Latin-American Conference on Communications (LATINCOM), on Oct 26th, 2011, in Belém/PA, Brazil. http://www.ieee-latincom.ufpa.br/

1. Opportunistic Networking: Extending Internet
Communications Through Spontaneous Networks
Waldir Moreira and Paulo Mendes
waldir.junior@ulusofona.pt
Oct 26th, 2011
IEEE Latincom 2011, Belém-PA/Brasil

2. Agenda
• Introduction
• The case of Delay/Disruption Tolerant
Networks
• Use cases
• Routing over Opportunistic Networks
• Future Directions
2

3. Introduction
3

4. Picture today
• Users are eager for retrieving/providing
information
• Popularization of portable devices
4

5. Opportunistic Networking
User
Willingness
Powerful
Devices
5

6. Opportunistic Networking
Opportunistic
Networking
6

7. Straightforward Definition
OppNets are highly dynamic, composed of
mobile and static nodes (i.e., devices) and
take advantages of opportunistic time-
varying contacts among users carrying
them to exchange information
7

8. OppNet Elements
• Nodes
- PDAs, cell phones, anything with networking capabilities
• Contacts
- Scheduled (i.e., mules, buses, LEO satellites)
- Opportunistic (i.e., random contact with a strange)
• Information
- Anything that can deal with the high queueing delays
8

9. General OppNets
Characteristics
• Occasional contacts
• Intermittent connectivity
• Highly mobile and fixed nodes
• Power-constrained devices
• Possible nonexistence of e2e paths
9

10. Application Scenarios
• Disaster and Emergency Networks
• Animal-Tracking Networks
• Sensor Networks
• Inter-Planetary Networks
• Delay/Disruption Tolerant Networks
10

11. The case of Delay/
Disruption Tolerant
Networks
11

12. Interplanetary Internet
"to permit interoperation of the Internet
resident on Earth with other remotely
located internets resident on other planets
or spacecraft in transit."
[9] Interplanetary Internet Home
12

13. Interplanetary Internet
[13] A. McMahon, S. Farrell. Delay- and Disruption-Tolerant Networking,
IEEE Internet Computing, 2009
13

14. IPN Characteristics
• Significant propagation delays
- 4 minutes one-way light-trip time between
Earth and Mars
• Intermittent connectivity
- Planetary movement
• Low and highly asymmetric bandwidth
• Relatively high bit-error rate
14

15. History
• Interplanetary Internet envisioned by Vint Cerf (1997)
• Collaboration between Cerf and NASA’s Jet Propulsion
Laboratory (1998)
• Interplanetary Internet Research Group (IPNRG)
• Interplanetary Internet (IPN): Architectural Definition
(2001)
• Delay-Tolerant Network Architecture: The Evolving
Interplanetary Internet (2002)
• IPNRG -> DTNRG
• Delay-Tolerant Networking Architecture (2007)
15

16. Simple DTN Definition
Occasionally-connected networks where
partitions are rather frequent
16

17. Regular Assumptions
• New networks do not have what it takes:
- Continuous, bidirectional e2e paths
- Short round-trips
- Symmetric data rates
- Low error rates
17

18. Why the need for DTN?
• DTNs can cope:
- Intermitent connectivity
- Long/Variable delay
- Asymmetric data rates
- High error rates
18

19. DTN Architecture
• Bundle layer
- e2e message-oriented overlay based on hop-by-hop transfer
with persistent storage to overcome network interruption
- Focus on reliable transport structure than in routing itself
19

20. Store-Carry-and-Forward
Paradigm
[16] W. Moreira and P. Mendes, “Survey on opportunistic routing for delay
tolerant networks,” SITI, University Lusofona, February, 2011
20

21. Use Cases
21

22. Different Environments
• Disruptive environments:
- Sparse scenarios where communication
is established through sporadic contacts
• Urban environments
-Dense scenarios with communication
suffering different interference levels
22

23. Disruptive Environments
Deep Space Communications
• Purpose: provide communication means
for manned/robotic exploration
• Main challenges: very long delays,
sparseness, shadow areas and spacecraft
lifetime
• Function: Information and commands are
exchanged between landers/rovers and
earth station through orbiters
23

24. Disruptive Environments
Deep Space Communications
[19] News on Deep Space Networking
[12] Mars Reconnaissance Orbiter
24

25. Disruptive Environments
Noise Monitoring
• Purpose: keep track of noise to ensure
acceptable levels
• Main challenges: high cost of equipments
and communication medium
• Function: buses (i.e., data mules) collect
data from monitoring stations
25

26. Disruptive Environments
Networks for Developing World
• Purpose: provide asynchronous Internet
access despite the scarce/expensive
infrastructure
• Main challenges: long delays and
scarce/expensive infrastructure
• Function: data is sent/retrieved either
through USB stick carried by a motorbiker
or via dial-up connection
26

27. Disruptive Environments
Networks for Developing World
[10] S. Jain, K. Fall, R. Patra, Routing in a delay tolerant network, 2004
[20] News on Pigeon Carrier
27

28. Disruptive Environments
Earthquake Monitoring
• Purpose: keep track of seismic activity
• Main challenges: very long delays
• Function: activity is relayed through
nodes until reaches the sink
28

29. Disruptive Environments
Earthquake Monitoring
[14] Middle America Subduction Experiment (MASE)
29

30. Disruptive Environments
Undersea Acoustic Networking
• Purpose: provide connectivity to
autonomous underwater vehicles
• Main challenges: delay, and challenging
medium
• Function: information exchanged
between AUV/subs and command center
through repeaters, buoys, and sattelite
links
30

31. Disruptive Environments
Undersea Acoustic Networking
[21] Seaweb Network
31

32. Disruptive Environments
Zebranet
• Purpose: Study zebra movements
through collars carried by them
• Main challenges: energy constraints
• Function: collars opportunistically
exchange GPS location later then
obtained by scientists
32

33. Disruptive Environments
Zebranet
33

34. Disruptive Environments
Sámi Network Connectivity
• Purpose: provide location information on
reindeer herds
• Main challenges: very little infrastructure
and sparseness
• Function: herds locations is carried on
snowmobiles back to villages
34

35. Disruptive Environments
Tactical Military Networks
• Purpose: establish quick communication
means among military soldiers, vehicles,
and aircrafts
• Main challenges: high disruption and
partition
• Function: information is relayed among
military units
35

36. Disruptive Environments
Tactical Military Networks
[15] MITRE Corporation
(C2 On-the-Move Network, Digital Over-the-Horizon Relay)
36

37. Urban Environments
Opportunistic Sensing
• Purpose: gather information from sensing
systems
• Main challenges: short contact times
• Function: sensor present in different
devices gather information which is then
collected mobile devices (i.e., custodian)
to be transfered to the sensing system
central
37

38. Urban Environments
Opportunistic Sensing
[3] CamMobSens - Cambridge University Pollution Monitoring Initiative
38

39. Routing over
Opportunistic Networks
39

40. What is it about?
Considers any contact among nodes and
forwarding decisions are made using locally
collected knowledge about node behavior to
predict which nodes are likely to deliver a
content or bring it closer to the destination
40

41. 2000-2010 Analysis
[16] W. Moreira and P. Mendes, “Survey on opportunistic routing for delay
tolerant networks,” SITI, University Lusofona, February, 2011
41

42. Existing Taxonomies
[16]
42

43. Major Routing Families
[16] W. Moreira and P. Mendes, “Survey on opportunistic routing for delay
tolerant networks,” SITI, University Lusofona, February, 2011
43

44. Flooding-based
Approaches
• Function: replicate messages at every
encounter
• Advantages: optimal delivery probability
• Disadvantages: elevated resource
consumption
44

45. Flooding-based
Approaches
• Epidemic
[24] A. Vahdat, D. Becker, Epidemic routing for partially connected ad hoc
networks, Tech. Rep. CS-200006, Duke University, 2000.
45

46. Forwarding-based
Approaches
• Function: only one copy of the message
traverses the network
• Advantages: spare resources
• Disadvantages: low delivery rate and high
delay
46

47. Forwarding-based
Approaches
• Direct transmission
- Forwarding only to the destination
• Utility-based routing with 1-hop diffusion
- Function based on encounter timers
[23] T. Spyropoulos, K. Psounis, C. S. Raghavendra, Efficient routing in
intermittently connected mobile networks: the single-copy case, 2008
47

48. Replication-based
Approaches
• Function: spread enough copies to quickly
reach destination
• Advantages: increase delivery probability
while sparing resources
• Disadvantages: metadata overhead
48

49. Replication-based
Approaches
• Encounter-based
• Resource Usage
• Social Similarity
49

50. Replication-based Approaches
Encounter-based
• Frequency Encounter: history of encounters with a
specific destination
- Encounter-Based Routing (EBR)
* Counts the number of contacts (Current Window
Counter)
* Determines node’s past rate of encounters
(Encounter Value)
[18] S. Nelson, M. Bakht, R. Kravets, Encounter-based routing in DTNs,
2009
50

51. Replication-based Approaches
Encounter-based
• Aging Encounter: time elapsed since last
encounter with destination
- FResher Encounter SearcH
(FRESH)
* Time elapsed
since last encounter
[7] H. Dubois-Ferriere, M. Grossglauser, M. Vetterli, Age matters: efficient
route discovery in mobile ad hoc networks using encounter ages, 2003
51

52. Replication-based Approaches
Resource Usage
• Aging Message: avoid messages to be kept
being forwarded
- Spray and Wait
* Spread L number of copies
* Direct transmission
[22] T. Spyropoulos, K. Psounis, C. S. Raghavendra, Spray and wait: an
efficient routing scheme for intermittently connected mobile networks,
2005
52

53. Replication-based Approaches
Resource Usage
• Resource Allocation: forwarding decisions
that wisely use available resources
- RAPID
* Replication occurs based on the effect
that it may have on a predefined
performance metric
[2] A. Balasubramanian, B. Levine, A. Venkataramani, Dtn routing as a
resource allocation problem, 2007
53

54. Social Aspects:
The New Trend
• Since 2007
• Have shown great potential
• Use social relationship
• Much wiser decisions
54

55. Replication-based Approaches
Social Similarity
• Community Detection: creation of communities
considering people social relationships
- Bubble Rap
* Forwarding based on
community and local/
global centrality
[11] P. Hui, J. Crowcroft, E. Yoneki, BUBBLE Rap: Social-based Forwarding in
Delay Tolerant Networks, 2011
55

56. Replication-based Approaches
Social Similarity
• Shared Interests: nodes with the same interest as
destination are good forwarders
- SocialCast
* predicted node’s co-location (probability of
nodes being co-located with others)
* change in degree of connectivity (mobility and
changes in neighbor sets)
[5] P. Costa, C. Mascolo, M. Musolesi, G. P. Picco, Socially-aware routing for
publish-subscribe in delay-tolerant mobile ad hoc networks, 2008
56

57. Replication-based Approaches
Social Similarity
• Node Popularity: use of social information
to generate ranks to nodes based on their
position on a social graph
- PeopleRank
* Forwarding based on social ranking of
nodes
[17] A. Mtibaa, M. May, M. Ammar, C. Diot, Peoplerank: Combining social
and contact information for opportunistic forwarding, 2010
57

58. Drawbacks with Detection
of Social Structures
• Community detection, shared interests, node popularity
• Communities are statically defined
• Do not consider the age of contacts when computing the
centrality
• Strong assumptions
• Full knowledge on social information is not enough
• Some social metrics (e.g., betweenness centrality) can
lead to node homogeneity
[8] T. Hossmann, T. Spyropoulos, F. Legendre, Know thy neighbor: Towards
optimal mapping of contacts to social graphs for dtn routing, 2010
58

59. Future Directions
59

60. Recap
• Lots of users
• Different new types of networking
• Many options to perform forwarding
60

61. Community-based
Forwarding
• Based on destination's community
- e.g., Kclique
[11] P. Hui, J. Crowcroft, E. Yoneki, BUBBLE Rap: Social-based Forwarding in
Delay Tolerant Networks, 2011
61

62. Interest-based
Forwarding
• Data travels based on interest
• Publish-Subscribe paradigm
• Next-hop node is chosen based on its
interest in the message's content
62

63. Information-Centric
Forwarding
• Focus on the content and its interested
parties
• Data is labeled (which is used to retrieve it)
• Users seamlessly exchange data among
themselves
[1] The FP7 4WARD Project
63

64. Acknowledgements
To FCT for financial support via PhD grant
(SFRH/BD/62761/2009)
64

65. Your view
What do you envision ??
65

66. References
[1] 4WARD Project, The FP7 - http://www.4ward-project.eu/index.php?id=29
[2] A. Balasubramanian, B. Levine, A. Venkataramani, Dtn routing as a resource allocation problem, in: Proceedings of
ACM SIGCOMM, Kyoto, Japan, August, 2007.
[3] CamMobSens - Cambridge University Pollution Monitoring Initiative - http://www.escience.cam.ac.uk/mobiledata/
[4] V. Cerf, S. Burleigh, A. Hooke, L. Torgerson, R. Durst, K. Scott, K. Fall, H. Weiss, Delay tolerant network
architecture, IETF Network Working Group. RFC 4838, 2007.
[5] P. Costa, C. Mascolo, M. Musolesi, G. P. Picco, Socially-aware routing for publish-subscribe in delay-tolerant mobile
ad hoc networks, Selected Areas in Communications, IEEE Journal on 26 (5) (2008) 748–760.
[6] Delay-Tolerant Networks Home - http://www.dtnrg.org/
[7] H. Dubois-Ferriere, M. Grossglauser, M. Vetterli, Age matters: efficient route discovery in mobile ad hoc networks
using encounter ages, in: Proceedings of ACM MobiHoc, Annapolis, USA, June, 2003.
[8] T. Hossmann, T. Spyropoulos, F. Legendre, Know thy neighbor: Towards optimal mapping of contacts to social
graphs for dtn routing, in: Proceedings of IEEE INFOCOM, San Diego, USA, March, 2010.
[9] Interplanetary Internet Home - http://www.ipnsig.org/
[10] S. Jain, K. Fall, R. Patra, Routing in a delay tolerant network, in: Proceedings of the ACM SIGCOMM, Portland, USA,
August,2004.
[11] P. Hui, J. Crowcroft, E. Yoneki, BUBBLE Rap: Social-based Forwarding in Delay Tolerant Networks, To appear in:
Mobile Computing, IEEE Transactions on, 2011.
[12] Mars Reconnaissance Orbiter - http://www.nasa.gov/mission_pages/MRO/news/mro-20060912.html
[13] A. McMahon, S. Farrell. Delay- and Disruption-Tolerant Networking. IEEE Internet Computing, 2009.
66

67. References
[14] Middle America Subduction Experiment (MASE) -
http://www.gps.caltech.edu/~clay/MASEdir/MASEprogress_report.html#Figure1
[15] MITRE Corporation (US Marine Corps) (Presentation on C2 On-the-Move Network, Digital Over-the-Horizon Relay) -
http://www.ietf.org/proceedings/65/slides/DTNRG-2.pdf
[16] W. Moreira and P. Mendes, “Survey on opportunistic routing for delay tolerant networks,” Tech. Rep. SITI-TR-11-02,
Research Unit in Informatics Systems and Technologies (SITI), University Lusofona, February, 2011.
[17] A. Mtibaa, M. May, M. Ammar, C. Diot, Peoplerank: Combining social and contact information for opportunistic
forwarding, in: Proceedings of INFOCOM, San Diego, USA, March, 2010.
[18] S. Nelson, M. Bakht, R. Kravets, Encounter-based routing in DTNs, in: Proceedings of INFOCOM, Rio de Janeiro, Brazil,
April, 2009.
[19] News on Deep Space Networking - http://www.engadget.com/2008/11/19/nasas-interplanetary-internet-tests-a-
success-vint-cerf-triump/
[20] News on Pigeon Carrier - http://www.dailymail.co.uk/news/article-1212333/Pigeon-post-faster-South-Africas-
Telkom.html
[21] Seaweb Network (Presentation)- http://www.ietf.org/proceedings/65/slides/DTNRG-14.pdf
[22] T. Spyropoulos, K. Psounis, C. S. Raghavendra, Spray and wait: an efficient routing scheme for intermittently
connected mobile networks, in: Proceedings of ACM SIGCOMM WDTN, Philadelphia, USA, August, 2005.
[23] T. Spyropoulos, K. Psounis, C. S. Raghavendra, Efficient routing in intermittently connected mobile networks: the
single-copy case, IEEE/ACM Trans. Netw. 16 (1) (2008) 63–76.
[24] A. Vahdat, D. Becker, Epidemic routing for partially connected ad hoc networks, Tech. Rep. CS-200006, Duke
University, 2000.
[25] F. Warthman, Delay-tolerant networks (dtns): A tutorial, Warthman Associates. Version 1.1, May, 2003.
67

68. Opportunistic Networking: Extending Internet
Communications Through Spontaneous Networks
Waldir Moreira and Paulo Mendes
waldir.junior@ulusofona.pt
Oct 26th, 2011
IEEE Latincom 2011, Belém-PA/Brasil