I've been testing the Madwifi driver for some time in Adhoc (IBSS) and AP / Sta modes.
For my latest tests I used the trunk version (rev 3408).
I have DLink cards using a 5212 chipset.
I did numerous throughput tests and found out that Adhoc will always give lower throughput than Ap / Sta mode.
In order to understand this issue I:
1. Fixed the rate (54 Mbits for example) to avoid the rate module.
2. Disabled AP background scanning.
3. Disabled any driver / hardware optimization (AR, XR, Turbo, FF, Burst, Compression).
4. Used a fixed channel that is clear (can't hear any other Sta / AP's)
5. Used a simple setup of 2 PC's connecting to each other.
The difference after all this is about 30% (16-17 Mbits in Adhoc mode vs. 20-21 Mbits in AP / Sta mode).
I looked in the protocol specification and I can't see a reason for this performance issue.
Can someone explain this situation?
Is it protocol related, implementation related or a bug?
I am willing to test the driver with other options / patches to see if it makes a difference.
Thanks for your time,