Wireless Bridge Backbone

André Luiz Ribeiro Moutinho andre.moutinho
Mon Feb 10 04:42:15 PST 2003


We are developing an application which is based on a 802.11 wireless
as described below:

     0(------------)0(------------)0(-- . . . --)0--------[control center]
   node 1         node 2         node 3        node N
 data source                                              data destionation

The nodes are based on SBC (single board computer) running linux. Each node
run 2 802.11 radio lan cards and each card will be connected to one branch
of the backbone.

The backbone will be used to transmit MULTIMEDIA (image, voice) contents.

At first, I thought There were 2 options to accomplish this:

1) Using N routers. Each node pair forming a network and constructing
   routing rules on each node of the backbone.

2) Replacing each node's couple wavelan card by a logical adapter forming 
   bridge. So, each node of the backbone will be on the same network.

Constraints on the above options where found:

1) The number of Wireless routers on a network is limited to a maximum of 3.
More than 3 hopes will lead to a timeout of ACK packages in level 2. This
will collapse the whole 
network performance.

2) 802.11 protocol has some architectural differences from standard ethernet
protocol.  Standard bridge setup on linux I have tried have failed.

Some research on the Internet lead me to some possible alternatives:

1) On some forum emails I have read that some firmware modifications could
be done but will demand a "very strong 802.11 protocol knowledge". 

2) Using vtun tunnel. Further details on http://vtun.sourceforge.net

3) Creating a bridge using cards having the prism chipset onboard
(manufactured by Harris Intersil). There are drivers for those cards
available at www.linux-wlan.com <www.linux-wlan.com>  (which is the website
from Absoval), and I found a mail that says that there is the necessary
firmware and an upload tool available for Linux to the public. If you need
additional features of an access point you should also talk to Absoval. 

4) Vladimir Ivaschenko has created parprouted, a daemon for transparent IP
(Layer 3) proxy ARP bridging. This allow to do "IP bridging" on any 802.11
card (instead of MAC bridging). http://www.hazard.maks.net/

5) InfoTech was developing a 802.11 software stack for Linux, including the
Access Point functionality. 
<http://opensource.instant802.com/what_is_openap.php>  (Opensource version)

6) Jouni Malinen has developed a driver for the PrismII cards supporting
Host AP mode and bridging.
http://hostap.epitest.fi/ <http://hostap.epitest.fi/> 

We demand some urgent solution for our backbone solution. 
Any comments, suggestions or advice will be very appreciated
and useful.


Andre Moutinho
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