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nearest router

 
 
Patricia Shanahan
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      11-04-2006
Mark Jeffcoat wrote:
> http://www.velocityreviews.com/forums/(E-Mail Removed) writes:
>
>> Hi,
>>
>> I will try with a network newsgroup, but I sent my question here
>> because i'am doing an homework in java. The reason I would like to know
>> the first router (nearest one) is because i want to be able to know
>> where is the person with the pocket pc. I was supposed to do something
>> with infrared access point but the project aborded. So i was thinking
>> that maybe it was possible to do something with the ip data from the
>> network. Like, my pocket pc can send a packet in a specified interval
>> of time to a server and the server or the pocket pc could determine the
>> position with the info. from the nearest router. In the university we
>> are using wireless network...
>>

>
> Wow. Are you trying to triangulate the position of the
> handheld computer by timing the response from multiple
> wireless routers? Because that would be a sexy project,
> though extremely ambitious if you don't already have a
> rough idea of what you're doing.


I don't think signal travel times would be very good. As well as the
issues you mention, any reflections would really mess things up. Most of
the systems I've read about or been involved in use either signal
strengths, or the set of access points with signals above a threshold.

Of course, GPS does use signal travel time, but the beacons are very
accurate clocks, and transmit timing signals so that a GPS receiver can
measure the differences in travel times extremely precisely.

>
> Seems unlikely that the the timing difference would
> map very well to physical differences, though, since
> the actual travel time of the signals is negligible.
> Maybe you'd end up with some sort of interference map?
>
> Ping estimates timings with ICMP, which Java definitely
> doesn't natively support. You'd need to go through JNI,
> or find some library that wraps the JNI for you.
>
>
> [Sigh. On my fourth reading of the post I'm replying
> to, I've decided that the original poster probably
> just wants to figure out, say, which building the
> pocket pc is in based on which router it's connected
> to. I just can't throw away the (hopeless) triangulation
> idea; I live in a house with two wireless routers and
> a Treo I lose all the time.]
>


There has been a lot of research on finding location from wireless
access point measurements. The Placelab publications page,
http://placelab.org/publications/, is a good starting point for seeing
the current state of the art.

Usually, location is driven off signal strengths, or the set of visible
beacons. Millions of access points have already been mapped - see
http://wigle.net/

Indoor location in office buildings does have problems with reflections
and variations in signal strength due to walls, floors, metal beams, etc.

The ActiveCampus project, which does indoor location using 802.11
wireless access points, has arrangements for user-entered corrections to
deal with some of those problems.

For a general description of ActiveCampus, see W. G. Griswold, P.
Shanahan, S. W. Brown, R. Boyer, M. Ratto, R. B. Shapiro, and T. M.
Truong, "ActiveCampus - Experiments in Community-Oriented Ubiquitous
Computing", IEEE Computer, Vol. 37, No. 10., pp. 73-81, October 2004.

Generally, 802.11 works much better than cell phones, but cell phones
are rapidly displacing 802.11 equipped PDAs as the common handheld
device. There is some hope for combined cell and 802.11 devices being
able to find themselves accurately.

Patricia

[Who should be getting on with her ubiquitous computing research instead
of reading newsgroups.]
 
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Mark Space
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Posts: n/a
 
      11-04-2006

> thanks anyway
> Daniel Pitts wrote:
>> (E-Mail Removed) wrote:
>>> hi !
>>>
>>> is there a java command or a property that I can check ?
>>>
>>> probably i can use traceroute, but it will be difficult because i use a
>>> pocket pc ?
>>>
>>>
>>> (E-Mail Removed) wrote:
>>>> The nearest router is the default gateway. There are some commands that
>>>> shows that, may be you can invoke the in your java programme.
>>>>
>>>> (E-Mail Removed) wrote:
>>>>> hi !
>>>>>
>>>>> I would like to know if there is a way to retrieve the ip or the name
>>>>> of the nearest router when we send a socket ?
>>>>>
>>>>> thanks

>> Maybe knowing why you need this, we'd be able to give more help.
>> Generally with network programming, you're not supposed to care/know
>> about the route. Information is generally sent in the form of
>> "packets" into a black box (the internet) and comes out the other side
>> in the same packet form.
>>
>> If you really must know the first IP in the route, then you need to
>> find a system specific way (try a networking newsgroup maybe?) and
>> implement it using JNI or an external process call.

>


(E-Mail Removed) wrote:
> Hi,
>
> I will try with a network newsgroup, but I sent my question here
> because i'am doing an homework in java. The reason I would like to know
> the first router (nearest one) is because i want to be able to know
> where is the person with the pocket pc. I was supposed to do something
> with infrared access point but the project aborded. So i was thinking
> that maybe it was possible to do something with the ip data from the
> network. Like, my pocket pc can send a packet in a specified interval
> of time to a server and the server or the pocket pc could determine the
> position with the info. from the nearest router. In the university we
> are using wireless network...
>


Hmm, I think "do something" is the problem here. Do what? You're a
coder in search of a customer.

I think first you should investigate Java thoroughly. You'll have to
know it really well if you are going to do tricky networking. Next
you'll have to figure out exactly what it is you want to do.

Java is a very high level language. Think further up the computer food
chain. Determining locations of close-by systems is relatively low
level. You should also check out some books on TCP/IP to learn it
better. Not programming books, per se, but books on how TCP/IP works.
Something like The Protocols (TCP/IP Illustrated, Volume 1) by W.
Richard Stevens .

Anyway, a neat app might be a Java applet than anyone can download on
their PC (pocket or otherwise) and chat over the wireless network.
It'll need a central server to send all the chat messages to and
download the app from.

Good luck.
 
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