802.11 xx "ad-hoc" mode

clockhar

Senior member
Dec 29, 2000
271
0
0
For the highly techincal:
I am doing a little research on how the 802.11 a,b,g, etc. standards are implemented. These wireless standards are able to exists in 'ad-hoc' or infrasture mode, right? Within ad-hoc mode, how does 'client a' know that 'client b' is still there? i.e. how do the clients know a client, that they've set up communications with already, is still online and hasn't been forced off the network? Is there a periodic "i'm here" packet sent by the clients to identify they're still around? Is it done in a better more efficent way?

Does anyone have any insight?
Thanks ahead of time.
 

Matthias99

Diamond Member
Oct 7, 2003
8,808
0
0
Well... I'd have to go look in the actual 802.11 specs to find what they really do, but I believe that if not too much time has passed since the last successful communication with another nearby system, and it wants to talk to that system (or to relay a message through him), it simply sends the message and tries to find another route if it doesn't get a successful response. If it's been a while, it might try to "ping" client B first, so as to not waste extra time/power transmitting a message that may just fail anyway. I don't believe the systems *continually* update each other on their status, although I do think they do send out an "I'm here!" occasionally (every few minutes) in order to discover new systems that may have wandered into range but just aren't broadcasting anything right now. Broadcasting an extra packet each time would slow down communications even more, and waste power.

But basically, no, there's no way to be 100% sure that a system which you were talking with is still there. But there's *never* any way to be sure of that, even in a wired network (it may just have crashed, for instance), so high-level networking protocols already take care of this. There's some extra stuff that has to happen in the bottom routing layers in an ad-hoc network that doesn't usually happen in an infrastructure network, though.
 

AFB

Lifer
Jan 10, 2004
10,718
3
0
I belive there is an Identifying Name similar to a SSID but for ad-hoc. Bssid?


PS: you might get better luck in networking.
 

Shalmanese

Platinum Member
Sep 29, 2000
2,157
0
0
If you want a simple way to think about it, each wireless card is acting as a mini-AP at the same time. It does all the functions an AP does for handling roaming, finding routes etc.