Spontaneous networks will speed net access

New Scientist                        Vol 181 Issue 2434                             February 2004, page 22

 

PEOPLE using cellphone networks to connect laptop PCs and PDAs to the internet could vastly increase their access speeds if they are willing to share their connections with those of people nearby.

That's the latest idea to emerge from Hewlett-Packard's research lab in Palo Alto, California, where software engineers say such "collaborative mobile networking" could allow groups of people to transform a sluggish link via the cellphone network into one capable of downloading large files in a flash.

Many of the latest mobile computing devices such as laptops, PDAs and smartphones are able to handle two different types of wireless connection. One is a Wi-Fi connection to a local wireless network that is in turn connected to the internet by a broadband landline. Wi-Fi gives access speeds of many megabits per second, but to use it you have to be within about 100 metres of a "hotspot" antenna - in an office, or in a cafe or airport lounge, say.

Outside Wi-Fi hotspots, these devices can access the internet via cellular phone networks, but these links are often far slower. On GPRS networks, sometimes called 2.5G, data rates are measured in tens of kilobits per second. HP's idea is that cellphone users who happen to be in Wi-Fi range of each other will pool their slower cellphone links in what it calls a collaborative mobile community, to create a faster link that each member can use in turn.

The new system, developed by Puneet Sharma and colleagues [SJ Lee, Jack Brassil, Kang Shin] in Palo Alto, relies on the fact that most people don't use the full capacity of their internet connection for more than the few seconds it takes to download a file. Typically they will then spend several minutes reading the file, leaving the bandwidth free.

Sharma's team is proposing to fit mobile devices with software that senses when similar devices are nearby - in a train carriage, for example - and spontaneously sets up a Wi-Fi network among them. Each device would also connect to the web via its own cellphone link.

In addition, HP's plan would require that cellphone companies or other service providers run a "community server" that keeps track of which devices belong to the ad-hoc network. When someone on the train requests, say, a video clip from the BBC, the request is intercepted by the community server, which passes it on to the BBC on the public internet. When the BBC's server starts sending packets of data, they go first to the community server. Then, instead of having to send them slowly down one cellular link, the community server will split the data stream between all the cellular links owned by the mobile devices on the train, making the transfer much faster.

When the collaborating mobile devices receive the packets making up the video clip, they send them on over the Wi-Fi network to the device that asked for the clip (see Graphic), which reassembles the data to recreate the original file. "It's oblivious to where it came from," says Sharma.

In a lab test involving downloading a 1-megabyte file, each of four mobile users was linked to the net via a simulated GPRS link, whose effective speed was 45 kilobits per second. But when they shared their links in a collaborative network, the peak bandwidth available to each one more than quadrupled to over 200 kilobits per second. As more users joined the community, the effective bandwidth available to each one increased, as the system automatically adjusted to the extra devices in the ad hoc community.

Sharma acknowledges that there are security concerns, though. For instance, a hacker could deliberately overwhelm a collaborative mobile community by streaming large amounts of data to it via the community server. This could also prevent users from receiving phone calls. But in such situations, he says, users could simply opt out of the community.

In exchange for faster access, people whose phones are linked to a community server will have to accept that at times their bandwidth will be used by other people downloading files. They may also find their phone's battery draining faster than usual as it downloads data for other people on the network. But Sharma thinks the success of peer-to-peer networks such as Napster suggests that this is a price people will be willing to pay. "It's not like charity. You are also benefiting," he says.

  Figure 1:



Anil Ananthaswamy