Hi Dan,
So far, with Linux, I have only used the iwconfig and iw tools. For one of the drivers, using iwconfig, I was able to set the data rate, which was used for broadcasts. I could set the data rate to both 802.11b and 802.11g rates. However, the hardware would send a CTS frame and apparently an 802.11g frame with what appears to be corruption giving a CRC error for all 802.11g rates. This only occurred when a node detects the presence of other nodes operating at 802.11b/g, which corresponds to 802.11n coexistence behavior. Not what I was expecting. For other drivers, I was unable to get anything but 1 Mbps broadcasts. As I think this is useful for floodfill types of data traffic requirements, as opposed to unicast or multicast, my next step is to take a look at the Linux MAC80211 layer. This is very much a "corner case" use for mesh networks, but I happen to need it. Still hoping for a simple solution to this.
David
On Thu, Jun 16, 2011 at 5:20 AM, Daniel Seither post@tiwoc.de wrote:
Hi!
Am 16.06.2011 00:04, schrieb David Beberman:
The second way I'm using it is to take advantage of broadcasting as a simply floodfill algorithm. All of my nodes transmit to all other nodes on a periodic basis. This is an IPv6 local multicast. I believe this translates to 802.11 MAC FF:FF:FF:FF:FF:FF broadcast address, and everything works.
What I noticed with a network sniffer is that all of the broadcasts were sent with 1 Mbps data rate.
This is the behavior specified in IEEE 802.11 [1], §9.6 (Multirate support): "All frames with multicast and broadcast in the Address 1 field that have a UP of zero shall be transmitted at one of the rates included in the BSSBasicRateSet parameter, regardless of their type or subtype."
The basic rate set seems to often consists only of small rates such as 1 or 2 MBit/s in 11g networks. However, I couldn't find out how to get the basic rates supported by my wifi card or configured in the wireless stack. Does anyone know how to do this?
- Daniel
[1] http://standards.ieee.org/getieee802/download/802.11-2007.pdf