The current Internet design falls short in scenarios characterized by intermittent connectivity and absence of supporting infrastructure. Pocket switched networking allows communication between portable handheld user devices in such environments through the store-carry-forward paradigm. This involves storing data in device memory, exploiting user movement to physically transport the data, and forwarding through available short-range wireless interfaces. In this regard, user devices can be leveraged as data mules for point-to-point communication in two main scenarios: (i) conveying data between major infrastructures in urban areas (e.g., transporting sensor data to gateways in smart cities); and (ii) extending wireless coverage to provide connectivity in developing regions (e.g., bridging user devices and remote Internet access points). User movement in such scenarios exhibit spatial locality, which is the preference to a geographical location than others. This feature influences the data transfer opportunities that exist between different sets of users. This paper investigates the impact of locality on routing in pocket switched networks by: (i) evaluating the performance of existing routing strategies for point-to-point communication over different degrees of locality; and (ii) providing insights towards enhancing routing performance for realizing the aforementioned application scenarios through locality awareness. This presentation was given in the 10th IEEE WoWMoM Workshop on Autonomic and Opportunistic Communications 2016 (AOC 2016), on June 21st, 2016 in Coimbra, Portugal.

1. Spatial Locality in
Pocket Switched Networks
June 21st, 2016
Tekenate E. Amah*, Maznah Kamat*,
Kamalrulnizam Abu Bakar*, Waldir Moreira†,¥,
Antonio Oliveira-Jr‡, and Marcos A. Batista§
The 10th IEEE WoWMoM Workshop on Autonomic and Opportunistic Communications (AOC 2016)
Coimbra, Portugal
*Dept. of Computer Science, Faculty of Computing, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia | †COPELABS, University Lusófona, Lisboa, Portugal |
¥PPGMO, Federal University of Goiás, Catalão, Brazil | ‡INF, Federal University of Goiás, Goiânia, Brazil | §IBiotec, Federal University of Goiás, Catalão, Brazil

2. Agenda
Introduction
Motivation
Methodology
Results
Towards locality aware PSN routing
Conclusions and Future work

3. Introduction
Ubiquitous portable handheld devices
Portable handheld devices form the center of human communication today
1
Store Carry Forward (SCF) communication
Communication via short-range wireless interfaces, user movement and opportunistic encounters
2
Pocket Switched Networks (PSNs) = Handheld devices + SCF
Opportunistic networks formed by user devices for non-real-time communications
3
Presents a scalable and resource efficient solution for data transfer
Urban: connecting major infrastructure | Developing regions: providing non-real-time connectivity
4

4. Motivation
User movement exhibits spatial locality
Users show preference to certain geographical locations or districts more than others
1
Locality affects encounter and data transfer opportunities
Lower locality presents more encounter opportunities, and vice versa
2
PSN routing strategies depend on encounter opportunities
There is need to understand the impact of locality on routing performance in PSNs
3
The impact of locality on point-to-point communication in PSNs
How does locality affect PSN routing and how can such routing benefit from locality awareness?
4

5. Methodology
The Helsinki city area in the Opportunistic Network Environment (ONE) Simulator
3 scenarios: locality is increased by including more overlapping districts
Small scenario
Low locality: 1 district
Medium scenario
Medium locality: 4 districts
Large scenario
High locality: 16 districts

6. Methodology
Simulation parameters
Parameter
Total simulation time (days)
Warm up period (days)
Wireless interface
Transmission range (m)
Transmission rate (Mbps)
Buffer size (Mb)
Value(s)
5
1
Bluetooth
10
2
100
Message size (Mb)
Message TTL (days)
Number of nodes
Ave. meg generation/node
0.5 to 1
1
19, 76 & 304
1 msg/hr

7. Results
Average delivery ratio
• Delivery ratio decrease
• Unlimited replication increases
buffer overflow
• Lower delivery ratio for
destinations farther away
• Spraying mitigates the ‘slow
start’ phase
Average overhead ratio
• Overhead ratio increase
• Increased locality requires more
replicas to reach destinations
• Unlimited replication increases
overhead
• Spraying controls the number of
replicas
Average delivery delay
• Delay increase (except SnF)
• Transitivity in the ‘focus’ phase
(in SnF) reduces delay
• Transitivity incurs storage
overhead

8. Towards Locality-aware PSN Routing
PRoPHET-LA
• Highly active nodes forward
messages traversing multiple
regions
• Others forward messages within
their home region
• PRoPHET-LA decreases
average overhead by 57%
SnF-LA
• The optimal value of L varies
over different degrees of locality
• The value of L for a message
depends on the home proximity,
p, of the source-destination pair
• SnF-LA varies L according to
L = 2(p+1)
PRoPHET-LA2
• PRoPHET-LA2 nodes maintain
only encounter information for
neighbours from their home
region
• 11% less delivery ratio, 84%
less overhead and 5% less delay,
with 88% less encounter
information stored

9. Conclusions and Future Work
Performance degradation
PSN routing performance
decreases over higher locality
Storage overhead
Storage overhead increases with
network size
Locality awareness
Locality awareness complements
existing routing strategies
Next steps
A measure for
locality
A study of the
concepts of locality
Validation of the synthetic
movement scenarios
Effects of locality on routing
fairness and energy consumption

10. Thank you
Acknowledgement: Thanks are due to Fundação de Amparo à Pesquisa do Estado de Goiás
(FAPEG) and PNPD/CAPES.