Archived from groups: alt.internet.wireless (
More info?)
On Thu, 18 Nov 2004 09:44:02 -0500, William P.N. Smith wrote:
>jiten dash <jiten.dash.1fx2oa@no-mx.forums.yourdomain.com.au> wrote:
>>I got a new project on WIFI technology. I am facing a problem. The
>>problem is when user is accessing my desktop application through
>>internet. I have to identify which Access point he is using. In other
>>words I want to find out the current physical location of the member.
>This homework assignment seems to come up a lot. There's really no
>way to know unless you know the entire topology of the network.
He also doesn't have a very clear description or understanding of the
problem.
My guess(tm) is that he wants to play TDOA (time difference of
arrival) direction finder on the internet. This has been done before
and is actually quite easy if you make some rather marginal
assumptions. If you assume that:
1. A ping return comes back via the same route that it is sent.
2. Latency for a given ICMP echo responder is constant.
3. Latency on backbones is fairly constant over short periods of
time.
4. The router doesn't delay ICMP or UDP echos using QoS.
5. You have a ping with better resolution than the usual 1 msec.
6. Whatever else I forgot.
What's necessary is to ping the IP address from a variety of distant
locations. I watched it work at a local university to locate roaming
hackers and student illegally deployed servers. By mapping the ping
times from various nearby known locations, the unknown responder can
be found by comparing the patterns. I was amazed to see a solution
converge in less than a second. It's not foolproof and requires some
tweaking and guesswork, but it does work.
As for identifying the access point in use, that can't be done with
simple tools from the internet (WAN) side. The local router/firewall
will block most probes aimed directly at the AP (which is on the LAN
side of the router). If there's any information to be found on the
WAN side, it must be sent (initiated) by the client or access point
and not polled from the internet (WAN) side.
--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558