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Unifying Undersea Wireless Communication Using TCP/IP
Nerval's Lobster writes "Wireless and cellular networks cover beaches and extend over the ocean to ships at sea but not, so far, under the ocean. A team of researchers at the University of Buffalo believe they've solved at least the technical problem of how to push wireless networking signals for long distances through the deep ocean to connect offshore oil and gas platforms, floating and underwater tsunami sensors and other remote facilities without having to bounce signals off a satellite first. Radio waves tend to be smothered or distorted by travel through water; most ocean-based sensors use acoustic waves instead, which link sensors into underwater acoustic sensor networks (UWASN). The team designed a low-power IPv4/IPv6-compatible networking protocol that uses very low power, compresses headers, is tolerant of fragmented data and connection delays, allows bi-directional communication with (and reconfiguration of) existing underwater sensors and is compatible with standard TCP/IP networks and IP router proxies. The approach is more than a simple translation from one networking medium to another. It leaves the higher-level TCP/IP networking protocols intact, but adds an adaptation layer between the data-link layer and network layer that compresses headers, changes packet size, transmission time-out settings and other requirements to be compatible with slower underwater transmissions. The team tested the implementation using a Linux-based driver, both PC and ARM-based computers and a Teledyne Benthos SM-75 Modem. They sealed two network nodes in 40-pound waterproof cases, dumped them into Lake Erie near Buffalo and transmitted instant-messaging signals from the application IPTUX from one to the other. They were also able to transfer files using FTP from an underwater client to server."
^ subject says it.
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It's a shitty day to be a whale.
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Yes they do travel through water. Their attenuation is frequency dependent and is given by the skin depth of water. Lower frequency waves propagate further than high frequency. At the wireless frequencies, water highly attenuates its propagation such that it can only communicate a few meters, but submarine ELF frequencies (73 Hz) can penetrate on the order of 1 km with only 60 dB loss or so, and ionospheric waves (approx .5 Hz) go through the complete ocean and into the lithosphere. [Source: Me. I am currently doing heavy research into this subject for a research contract] As a layman thinking only of WANs and 2.4 GHz stuff I could see how you could make this mistake, but what you way is false. Even GHz waves will travel, albeit an insignificant amount, but still finite.
Moderating /. posts takes longer under water.
Knowledge is how to play a game, intelligence is how to win, wisdom is knowing what game to play.
Finally, Spongebob gets dialup!
Not quite. Acoustic networking is a necessity in water, as compared to eM in space. Acoustic networking is also notorious for being easily influenced by its ambient environment (temperature, pressure, acidity, salinity). Not to mention the long delays, which can easily vary over the course of a single day many times. Add to this the mix of those special ambient conditions that can lead to "black-holes" where sound from outside doesn't enter, and you've got a mix of an environment that is a pain to handle.
That said, I am not sure the authors' work on essentially porting 6LoWPAN to UWAN is the right way to go since it doesn't account for many things, but it is a step in the appropriate direction. Though, honestly, equipping underwater sensors or vehicles with IP networking might be a bit of an overkill.
Long delays.
Sound travels at the speed of sound, which is a lot slower than light causing large delays. In space things are simply so far away that the light speed delays are similar.
If you have a 3 hour delay you do not wish to use the default TCP/IP, because the syn/ack phase would take hours.
My best guess is that you have a quite long sync phase and then just send the data and wait for confirmation that it's received correctly after sending everything. If it isn't received correctly you send the parts that went wrong again.
Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
How are they going to shoot us? Only sharks have lasers on their heads.
Close, but not quite the the same. I understand that background radiation, solar flares, planets, moons, comets and asteroids have a negative impact upon radio communication. However, this is something that we do understand how to deal with in some respect, given our history of working successfully with radio. I am not trying to say it is easy, but the challenge there is within the scope of technology that is better understood.
Also, while all those factors you mentioned pose problems, the underwater acoustic channel is still more volatile. Imagine a temperature shift of one degree, i.e. from morning to evening, completely changing your delay factor. Not just that, but as a result now your ideal frequency and power combination that obtains you optimal bandwidth is also different. Underwater nodes are also notoriously hard to get power to (and yes, I understand that there is no power station sitting in space either, but you still do have access to energy gathered from solar radiation and etc.), which makes switching all of this really hard to do.
Now add the factor that the depth of your transmitter and receiver might be different, and this results in both of them having a different set of optimal (or near optimal) communication requirements. Both might even have different windows of opportunity to work in, making synchronization near impossible to achieve. This is not counting the problem of ambient noise that keeps changing based on surface winds, thermal effects and waves. Add to this multi-path echoes that are quite plenty and you start to get an idea of some of the many issues that this channel is faced with.
In the end, yes, both channels are similar in the fact that there are long delays and to some extent these might vary in space as well. But the very nature of the underwater acoustic channel is different from radio in space. There might be some things that can be learnt from NASA's space-tuned TCP/IP stack, but in general, TCP/IP is a bad idea in a channel that can hardly carry a few bits at a time. In the case of 6LoWPAN, which the authors of the paper in question look to for inspiration, they have still more bits than what you get underwater. Header compression and similar things can help, but in the end, fragmentation and reassembly is not the best approach. Hence my previous statement that maybe, TCP/IP is not the best idea for underwater acoustic channels.
TLDR: Yes, the two channels have some similarities, but they are not the same thing. Will there be things that can be learnt by each field from looking at solutions in either fields? Sure, but that doesn't cover it all.
A lot. Air is almost non-conductive, whereas seawater is highly conductive, so the interface is highly reflective, and refractive.
Yes, thats all true. As I said above, its penetration depth is given by the frequency dependent skin depth of the medium. BUT, some things don't need much bandwidth, nowhere near as much as 1200 bps. And if the navy invested millions into a 28 mi antenna to produce that 76 Hz, the low bandwidth it gets, and the concept of radio in seawater, is obviously not that silly. http://en.wikipedia.org/wiki/Project_Sanguine
It's worse than that. The water temperature (and pressure) changes with depth, which means the speed of sound does as well. This causes sound initially heading down to arc back up, until it hits the surface and heads back down again and repeats (fig 12). Consequently, any sound which isn't traveling a short enough distance that it can travel straight to the target gets smeared out over time due to multipath.
It leads to some interesting phenomena. A thermocline (layer of water with an abrupt temperature change) can refract the sound enough to prevent it reaching anything underneath. Submarines sometimes use this to hide from sonar, but it will also block any listening devices you have from hearing what a surface station is broadcasting. And a SOFAR channel where the temperature forms an acoustic waveguide, allowing you to transmit sounds around the globe with little loss (though it adds a lot of distortion due to the multipath). Whales use this to "broadcast" their songs for thousands of miles.