Ad hoc Networking

Boxing day (December 26) of 2004 will forever be etched in our

memories. Struck the shores of Indonesia, Sri Lanka, India and others. It was

the day when the Tsunami stuck. While innumerable people died in the wake of the

flooding waters, thousands died in the aftermath, for want of medicine and food.

There was no real paucity of medicine and food packages. What

was lacking was a communication structure over which the relief process could be

coordinated. But how can relief agencies communicate, when the whole

infrastructure has been ripped apart? Satellite communication is quite dear

(cost wise) and often unreliable in cases of far-flung locations.

An alumnus from IIT-Delhi, based in the US, Pritwish Basu, is

currently working on a technology that will make all such concerns

(communications without infrastructure) redundant. A scientist at BBN

Technologies, Basu has developed algorithms that enable wireless devices to

interconnect with each other (ad hoc networks) with very low drop rates. For his

work Basu was recently awarded the prestigious TR35 award by MIT's Technology

Review.

What are Ad-hoc Networks?



He describes ad hoc networks as wireless networks that can be set up quickly
for communication between nodes, and do not require any infrastructural support

from satellites, cellular towers or base stations.

Unlike a traditional network in which all devices are linked to

a central hub, in an ad hoc network, all devices communicate with each other and

relay data forward.

It may seem fairly similar to the Wi-Fi network that is common

nowadays. Basu clarifies: "The similarity with Wi-Fi (IEEE 802.11a/b/g) or

WiMax is that an ad hoc network also may use similar wireless radio

transceivers. However, the difference is that in the case of Wi-Fi etc, there is

a static base station that is established a priori and that allows wireless

nodes to access the Internet. In the case of ad hoc networks, there is no base

station and nodes communicate directly with other nodes in their transmission

(radio) range, and they can help in cooperatively forwarding packets to remote

nodes that are not in direct communication range of the source node. There are

several well-known ad hoc routing protocols that can perform this task," he

says. Ad hoc networks symbolize cooperation, wherein one device collaborates

with another for transmitting data.

Mind-boggling Potential



Considering the nature of these networks, military applications come
naturally to mind. But as of now, defense forces use satellite communications

extensively. What is the real benefit they can derive from this emerging

technology? "Indeed, the military uses satellite networks for a lot of

their communication needs. But the bandwidth that is available over satellite

channels is usually inadequate to satisfy the communication needs. Ad hoc

networks are extremely useful when the nodes are localized (within a few kms or

tens of kms of each other) and have to communicate with each other. Then they

can get higher data rates with lower delays," says Basu, adding:

"Also, satellite signals are often inaccessible indoors and in dense

foliage. Needless to say, access to a satellite communication link often costs

several dollars per minute whereas ad hoc wireless links are free."

"The MAC and routing problems are what make ad hoc

networking very different from traditional wired IP networking or even wireless

cellular or Wi-Fi networks," emphasizes Basu. According to him, in an ad

hoc network, the MAC layer has to coordinate the order in which different nodes

transmit in a distributed manner because there is no luxury of a central

authority like the base station for computing the transmission schedule. The

routing layer too has a more difficult task. Whereas in wired IP networks,

hierarchical routing is feasible because nodes have static IP addresses which

can be aggregated into hierarchical sub-network addresses. This is not possible

in mobile ad hoc networks since nodes could be moving around. One mechanism of

computing routes is by periodically broadcasting the status of all current

neighboring links to all other nodes in the network. "A lot of research has

been carried out in the last decade for optimizing this process since the

wireless channel is much more resource-limited than a wired network. Recently,

people have been rethinking even the design of physical layers to benefit ad hoc

networking (eg, techniques such as cooperative diversity)," he says.

Ad hoc networks can play a major role in our day-to-day

business. For instance, Basu talks about networking parking meters that could be

configured through an ad hoc network. "One could have a transmitter on each

parking meter; then you add a sensor that can tell whether there is a car in

that spot. Thus, if a user wants a parking slot near his building all he does is

query on the console in his car. The query is sent to the nearest parking meter,

and if it isn't empty, the request would be forwarded to the next meter till

it finds a free spot, and then even reserve it, if possible," he says.

Buildings could also be networked on such sensorized mesh ad hoc

networks, he says. "If it is a bit chilly, the sensors in different windows

transmit a message, and they are closed automatically, thereby saving

heat," adds Basu.

"Blue tooth is the first true ad hoc product. It can

support up to 80 nodes, sadly till date it has only been used for cable or wire

replacement. It is a cool application, so is Zigbee," he says.

Battery life is one of the biggest challenges faced by the

industry. "Since the devices are constantly transmitting data, the battery

life could be a big issue. For that one needs to develop better protocols, or

dramatic gains in the battery technology is required," Basu adds.

In the years to come, Basu hopes to see a lot more ad hoc

networks, even in India. "The potentiality of ad hoc networks is mind

boggling-from saving lives, in case of natural disasters like the tsunami or

an earthquake, to making our lives easier and more happier. The future could be

quite like the science fiction movies that we often watch. We are getting closer

to that future with ad hoc networks," signs off an optimistic Basu.

Shashwat Chaturvedi



maildqindia@cybermedia.co.in