An Overview of Opportunistic

Communication

Kaushik Choudhary kaushik.choudhary@wipro.com

The emergence of extremely powerful mobile communication devices in recent times has

triggered off the development of many exploitative technologies that attempt at

leveraging the ever increasing processing, storage and communicating capacities of these

devices. These devices that are literally carried by users in their pockets are already

equipped with multiple wireless network interfaces making it possible for them to be

used over heterogeneous networks that differ in data rates, power consumption, monetary

costs and coverage areas.

1. Introduction

Opportunistic Communication is the moniker for one such technology that has been of

particular interest to researchers in recent times. Strictly speaking, opportunistic

communication is an interesting evolution from Mobile Adhoc Networks (MANETs) and

from Delay Tolerant Networks (DTNs). A MANET, also known as a mobile mesh

network, is a self configuring network of mobile devices connected by wireless links.

Each device in a MANET is free to move independently in any direction, and will

therefore change its links to other devices frequently. Such networks may operate by

themselves or may be connected to the larger Internet. While, DTN is an approach to

computer network architecture that seeks to address the technical issues in heterogeneous

networks that may lack continuous network connectivity. Examples of such networks are

those operating in mobile or extreme terrestrial environments, or planned networks in

space. Opportunistic Communication involves mobile nodes that are capable of

communicating with each other even if a route connecting them never exists! Moreover,

nodes are not supposed to be aware of the network topology at any given point which is

its fundamental difference from MANETs where the nodes are supposed to determine

and be aware of the network topology at any given point. The communication routes are

built dynamically while the messages are en route to the destination and the nodes or

hops are chosen entirely based on the condition that using the node brings the message

closer to the destination. In this article I intend to discuss the model for an opportunistic

communication network and a case study of real life implementation of opportunistic

communication outlining the information discussed by Pelusi et al [1]. Lastly, I will leave

the reader with some thoughts and open areas.

2. Model network

Multi hop ad hoc networks were originally conceived for military applications and aimed

at improving battlefield communication and survivability, research on such networks has

lately been interposing the realms of many civil scenarios. Opportunistic communication

is an evolutionary technology coming out this research. In opportunistic communication,

assumptions about the existence of a complete path between two communicating nodes

are never made. In fact, the source and destination node might never even be in the same

network at the same time. Nevertheless, opportunistic networking techniques allow such

nodes to exchange data between them. Of course, such communication techniques

succeed at the cost of delays in message deliveries and mandate the availability of

applications that can tolerate the delay while a message is buffered in the network waiting

to be delivered to the next possible node in the network that will take it closer to the

destination. Although building delay tolerant applications is a daunting task given the

consumer demands in today’s world but the task of building such a network poses a much

more compelling challenge.

Often the terms opportunistic communication and delay tolerant networking are used

interchangeably due to the inexistence of a concordant formal definition in the literature

for both terms. In an opportunistic network, routes are determined at each hop while a

packet traverses different hops. Each node is equipped with local knowledge of the best

nodes around it and it uses this knowledge to determine the best path to transmit the

message to the eventual destination. In the absence of any such nodes, the node currently

holding the message simply stores the message and waits for an opportunity. In DTNs the

routes are determined using legacy internet technologies while keeping the cost of

unavailability of a link under consideration. In opportunistic networks each node acts as a

gateway which makes it much more flexible than DTNs.

Figure 1: Opportunistic Networking. [1]

Figure 1 shows an exemplary model for opportunistic communication. The hop by hop

communication takes place in the following steps:

1. The woman on the left at her desktop opportunistically

transfers a message for a friend via a Wi-Fi link in

the bus passing by her home.

2. The communication begins with the hope that the bus

will somehow “ferry” her message (data packet) to the

intended receiver. The bus moves travels through the

traffic and passes on the message to the mobile phone

of a girl getting off at one of the bus stops using

the Bluetooth radio.

3. The girl walks through a park where she transmits the

message forward to a cyclist passing by.

4. Proceeding in the same way, some hops later, the

message eventually reaches the receiver.

As it may be clearly seen, the two women never existed in the same network nor were the

participating nodes aware of a fixed data path to deliver the message. The message

traversed opportunistically to reach the receiver.

3. Real life case studies

Apart from the ambitious haggle project (http://www.haggleproject.org), which is EUs

initiative at studying and researching solutions in opportunistic networks there are other

possible implementations as well. Wildlife monitoring and tracking is one such

interesting field where opportunistic communications finds an indispensable use.

Researchers try to track wild species to understand their habitats and behaviors and their

interactions and influences on each other. Opportunistic networks serve as a cost-

effective, unintrusive and reliable means of arranging for the collection of this data. In

such systems, animals under study wear sensor tags which are capable of collecting and

sending data to the few base stations located around their habitat. Sometimes these base

stations may be mobile. Collating data collected by these base stations from the different

sensors is a challenging task and so the sensors are always made to communicate with

each other in order to synchronize all data available to them at a given point. This enables

a base station to collect maximum possible data from one single animal and also as a

results of its proximity or interaction with other animals carrying these sensors. The

ZebraNet project (http://www.princeton.edu/~mrm/zebranet.html) is one such

implementation of this technology and is deployed over the vast savanna area of central

Kenya under the control of Mpala Research Center in collaboration with Princeton

University. [2]

There are many other possible implementations including deployment in rural areas in

underdeveloped and developing countries where the network infrastructure for legacy

Internet connections is virtually absent and this technology serves as the only cost-

effective way of providing intermittent but existent internet connectivity in these areas.

Such systems have already been under development and have seen deployment in India.

The DakNet project [3] and the KioskNet project [4] are prime examples.

4. Challenges

One of the major challenges of implementation of opportunistic networks is the absence

of a consistent route or data path. The design of efficient routing strategies in

conventional networks is usually based on the knowledge of the available infrastructure

and the network topology, whether physical or logical. Unfortunately, such knowledge is

not available in such networks as the formation of data path is entirely opportunity based.

For achieving a reliable data path a trade off against the performance of the network must

be met before designing the routing strategy. Opportunistic networks may or may not be

infrastructure based. An infrastructure based network may have fixed or mobile nodes

while a non-infrastructure based may be contextual and purely opportunity based. A

thorough study and analysis on design strategies and possible topologies in opportunistic

networks is presented in [5] and [6]. Investigation into security strategies for such

heterogeneous topologies remains as another challenge for researchers as conclusive

work towards implementation impends.

5. Conclusion

Opportunistic Communication presents a profitable prospect to business owners by

offering extremely low cost and sometimes even zero investment infrastructure

requirements. With the usage of powerful and smart mobile devices only poised to

proliferate, this area of communication poses innumerable opportunities. The DakNet and

KioskNet projects exemplify inspirational usage of research and technology to address

demands which technology should be ideally addressing – service to the common man.

Flow of information paves way for transformation that one can hardly imagine. The use

of opportunistic networks will pave way for groundbreaking methods of information

dissemination and it only remains to be seen what a common man can do with

overwhelming information that will be delivered to him via the internet. Aside from that,

business opportunities will come abound should one try and tap the immense potential in

the vast rural markets where the government programs fund projects on empowerment.

Unbeknownst to none is that Government programs are intrinsically slow paced which

presents a great opportunity for businesses to consider this low investment market which

will not only pay dividends in terms of returns on investments but will also help the

popularity of a business for taking up a noble endeavor. Essentially, opportunistic

communication presents its case as a win-win situation. These rural markets are not just

limited to India but to the majority of developing nations all around the world. The

possibilities are only limited by one’s imagination.

References

[1] L. Pelusi, A. Passarella, M. Conti, “Opportunisitic Networking: Data forwarding and Disconnected

Mobile Ad Hoc Networks Export”, IEEE Communications Magazine, Vol. 44, No. 11. (November 2006),

pp. 134-141.

[2] P. Juang, H. Oki, Y. Wang, M. Martonosi, L.S. Peh, and D.I. Rubenstein, “Energy-efficient computing

for wildlife tracking: Design tradeoffs and early experiences with ZebraNet”, ACM SIGPLAN Notices,

vol. 37, 2002, pp. 96-107.

[3] A. Pentland, R. Fletcher, and A. Hasson, “DakNet: Rethinking Connectivity in Developing Nations”,

IEEE Computer, vol. 37, no. 1, January 2004, pp. 78-83.

[4] S. Guo, M.H. Falaki, E.A. Oliver, S. Ur Rahman, A. Seth, M.A. Zaharia, U. Ismail, and S. Keshav,

“Design and Implementation of the KioskNet System”, International Conference on Information

Technologies and Development, December 2007.

[5] L. Pelusi, A. Passarella, and M. Conti, “Beyond MANETs: dissertation on Opportunistic Networking”,

IIT-CNR Tech. Rep., May 2006, online available at http://bruno1.iit.cnr.it/~bruno/techreport.html.

[6] Z. Zhang, “Routing in Intermittently Connected Mobile Ad Hoc Networks and Delay Tolerant

Networks: Overview and Challenges”, IEEE Communications Surveys, vol.8, no.1, First Quarter 2006.

[7] http://en.wikipedia.org/wiki/Delay-tolerant_networking

[8] http://en.wikipedia.org/wiki/Mobile_ad_hoc_network