Distruption-tolerant networks: great emergency communication tool

12/13/06

Wow! Here’s one of the final missing links in my networked homeland security strategy: an innovative technology that had this observer looking back to 1860 and to a playground game of tag.

Let me explain…

Network World had a feature on distruption-tolerant networks (DTN), mobile nets that continue to work even if there are “… broken links and long delays.” The trade-off is that it can take longer to send and receive data — understandably, since these nets are marked by “frequent and unpredictable disconnections, changing nearby nodes, and very long delays.” However, when the alternative is no communication at all, which is frequently the case during a disaster for conventional, fixed networks, that intermittent access looks better and better.

Much of the work on DTN is being done near hear, at Internet pioneer BBN Technologies in Cambridge. under a DARPA grant. They simulated a 20-node DTN with each node available only 20% of the time, but were able to deliver 100% of the packets transmitted.

The key was to alter the normal packet structure of Internet messages.
Normally, there’s an end-to-end path for routing the packets. “But,” as
the article points out, “all that breaks down when the network ruptures
because of repeated disconnnections and long long delays. BBN has
developed a network protocol and code that moves information from node
to node as connection become available, and can hold information in
persistent storage until a connection is available.” Based on the
experiment’s success, BBN is created a full reference implementation of
the DTN routing protocol (”Bundle”) plus a hardware and software
platform incorporating it. They will also create APIs so “third parties
can substitute their own code for some parts of the DTN system, and
creating code that will let the DTN software elements run over different
types of underlying network transports..” including Ethernet, Bluetooth
and 802.11.

DTN’s already being implemented at
UMass,UMass Diesel Net map which has mounted the system in 40 buses on its campus
(hence, “DieselNet”!). As buses with the computer/GPS/radio
combinations near each other, the DTN nodes “… query each other to
find out what other nodes each sees most frequently. If another node
is related to the final network destination of a message, that message
is handed off to the passing node in the second the buses are close
enough for the Wi-Fi connection. At some point, the message is handed
to a node attached to the wired Internet.” Is that cool, or what?

Whoa! Consarn it! Wait just a darned second, here, big fella! Didn’t this here message
delivery system run from April 3, 1860 through October, 1861, from St.
Joe Missouri to Sacramento?? Ain’t it called the Pony Express? Sure
do sound like the same idea, don’t it?

Oops, pardon my John Wayne moment.

When DieselNet launched in the spring, the article says the median
amount of data transferred between buses was 1 MB in 10 second, and now
it’s about half that amount in 8 seconds, perplexing the researchers.
Now they’re testing stationary, wireless nodes called “throw boxes,”
powered by PV panels and batteries, on buildings along the route: the
packets are transferred from the bus to the box until another bus
passes. Tag, you’re it!

WiFi laptops on the buses can access cached information, including bus
routes, news, and weather. Eventually, users will be able to get
information from the Web a la the Cedar
Rapids mobile Internet cafes (AKA the city bus lines) I wrote about
last year although a lot slower (but again, that’s not the point:
we’re talking some access, rather than none). It’s also reminiscent of Kurt Keville’s proposal for
a PV or wind-powered stationary homeland security communications
communications network.

The Network World article also deals with another problem of a disrupted system:
information searches: you can’t just Google stuff:

“To compensate, the BBN researchers are
combining the new routing protocol with a technique called ‘late
binding.’ In a DTN, messages can be launched from a source node en
though the final destination’s IP address can’t be known because of
disruptions of name servers or routers. In effect, the message has
blank spaces for the naming and address information.

“‘The message makes its way through the network, and the blanks get
filled in,’ BBN’s [Rajesh] Krishman says. Eventually, the destination
IP address-binding takes place.”

The article concludes with discussion of a new caching method for DTNs,
which would track the cached content and respond to requests.
Eventually, they foresee a system in which “.. information requests
(who wants to know what) move through the network and meet information
advertisements (who knows what).”

The example they use is real 21st century stuff: a scout troop in the
woods, led by a scoutmaster with a wireless PDA with maps of the route
(these aren’t your 1990s scouts, after all…). He still gets lost, and
uses the PDA to request new maps from Google. However, because he
doesn’t have a WAN connection, the request to Google doesn’t go
through. Never fear: when Scoutmaster Chuck broadcasts the request, it
turns out “Scout Billy has maps of the area stored in the browser cache
of his PlayStation Person, which returns the map to Chuck’s PDA.”

From the Pony Express to Scout Billy’s PSP, it definitely seems to me disruption-tolerant networks are a major trend to watch. IMHO, while blindingly fast data transmission is cool and essential,
when it comes to emergency communications, DTN is really an astonishing and equally vital accomplishment: in a
crisis such as Katrina or after a terrorist attack, with the potential that much of the fixed communications
infrastructure is compromised or has gone kerfluie, some wireless
communication is better than none. Bravo, BBN and UMass!

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