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Communicating Even When the Network Is Down
coondoggie writes to mention a NetworkWorld article covering efforts to maintain network connectivity even when the network has holes. Building off of the needs of the military, the end goal is to create a service which will route around network trouble spots and maintain connectivity for users. From the article: "Researchers at BBN Technologies, of Cambridge, Mass., have begun the second phase of a DTN project, funded by $8.7 million from the Department of Defense's Defense Advanced Research Projects Agency (DARPA). Earlier this year, the researchers simulated a 20-node DTN. With each link available just 20% of the time, the network was able to deliver 100% of the packets transmitted." The article is on five small pages, with no option to see a linkable, printable version.
"But all that breaks down when the network ruptures because of repeated disconnections and long delays. BBN has developed a network protocol and code that moves information from node to node as connections become available, and can hold information in persistent storage until a connection is available. " They are solving the case when at each point in time, there is *no* end-to-end path. ARPANET assumes there is at least one path, though the path can vary over time.
A real criticism of what BBN is doing is that, heck, my cell phone is low enough on memory already--and I would be very put out having to share that meager space in order to persist that scoutmaster request for google earth maps. Also, think about how that mechanism would have to be configured--does every scout have to "allow" the scoutmaster to query/query-through their PDA's? How complicated would that be? If BBN decides to simplify it by allowing a certain level of adhoc-ness, then what would be the security ramifications?
I suppose that that's why this is a DARPA project (which connotes research)--because I think there is no way this can be more than an experiment.
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This is an old wive's tale that deserves to die. The ARPANet was NOT built as an experiment in resiliant networking; it was built by DARPA to connect scientists so they could share all the large computers that DARPA was funding.
e rnet/dp/0684832674
See: Where Wizards Stay Up Late
http://www.amazon.com/Where-Wizards-Stay-Late-Int
and
http://www.businessweek.com/1996/38/b349359.htm
The goal of the Arpanet was to provide resilient packet forwarding in the presence of multiple node failures. However, the Arpanet model does assume that at any given moment there is end-to-end connectivity between the two communicating endpoints. DTNs do not assume that there is necessarily *ever* a direct, end-to-end connection between communicating endpoints. DTNs are store-and-forward networks, much like email or UUCP, they don't look anything like Arpanet or the Internet.
It is clear from the article that they are aiming for something more than OSPF or other link state routing protocols. If a link is cut inside a network, OSPF adjusts so that traffic is routed through alternative paths. But, until there is convergence (which is quite fast in most cases), packets may be lost. Packet drops do tend to occur if a router cannot find a suitable route to a destination, if it is able to find a route but the link to that route is down, or even if the queue on that link is congested (full). That's the very nature of our present best effort internet.
It appears to me that these guys try to address some of these "shortcomings" by making certain privisions that can guarantee packet delivery, even in a overly late fashion. A routing instability, lost routes or links should not be able to cause packet drops if they have it right.
However, I used the quotes in "shortcomings" because I am not entirely certain that this has not been tried before. If, instead of a best effort packet routing service, you try to invent a "smart" network layer that can guarantee stuff like ordered delivery (packets are delivered in the order they departed), assured delivery (even with great delays) etc, you are basically trying to invent a (gasp!) connection oriented service. Not that connection oriented technologies are inherently bad, but, well, they are certainly an order of magnitude harder to implement. Anyone remembers OSI? It might as well be easier to leave IP simple as it is and try to move some smartness to the upper layers.
Additionally, it would be better to try to build on top of unreliable services like IP and construct stuff like SMTP (as a previous poster very cleverly pointed out), that can function even if parts of the network are mulfunctioning.
Well, anyway, you might want also to take a look at the efforts on the interplanetary internet, this article reminded me of it.
No, this has not been done before in this manner. The internet does not communicate when disconnected. Try to send a file to a machine that is turned off or not connected to the net and see what you get?
This type of network, DTN (Disruption tolerant network - which btw, is similar to DTN - delay tolerant network - (see IETF working group)) is oriented towards disconnected operation, mobile nodes and ad-hoc environments.
BBN is not the only participant (though it is a big one). The project includes various universities and research institutes.
Look for DTN to be used in upcoming NASA missions (see interplanetary internet) as well as next-generation military networks. DARPA and NASA are serious about this, and have Vint Cerf's backing as well. I expect that there will be quite a few commercial-off-the-shelf solutions that spin off once the dust settles around the standard.
It won't replace the current internet protocol suite - just augment it.
No, they named algorithms after an Arabic mathematician named Al-Khwarizmi(Algorismus). He translated a lot of greek works too. Check him out. Some of his translations and original work form the basis of what has become algebra, which is another etymological contribution from him.
SRSLY.
Actually, a planned convergence layer for the DTN project is sneakernet.
DTNs work by storing packets (well, "bundles," really) at the router, until an opportunistic connection is available. Bundles move from hop to hop, until they arrive at their destination.
This is accomplished over a variety of "convergence layers," such as TCP and UDP, with UDP being the most commonly used for transmitting bundles currently in research. However, other convergence layers for other uses are being planned. One of these is sneakernet, where data is copied to physical media, the media is physically taken over to another node, and the other node reads the data and forwards the bundles to the next hop as available.
The main research page is at http://dtnrg.org/.
They carry endpoint IDs, which achieve a similar functionality to IP addresses and TCP/UDP ports, but are also human-readable. DTN protocols are fairly high-level, so they can do that.