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Wifi over USB, focus Access Point-usage

Question asked by Rob. on Jul 19, 2013
Latest reply on Jul 23, 2013 by Aaronwu

In doing experiments with hostapd, I encounter serious issues that partially do not appear when wifi is operated as a client.


Mainly, 2 driver families represent main choices in the xconfig tree: Atheros (standard & carl9170) and Ralink, and some other choices exist, e.g. Realtek.


I'd like to collect experiences from other users as well as from the ADI guys. Here are my experiences:


Ralink 8192cu is currently subject to data alignment crash, and hence no more experiences are made.

Atheros ath9k_htc and Ralink rt2800usb are doing the jobs as AP quite good, but with some restrictions:

- ath9k_htc perform very stable using iperf tests, but during iperf sessions, other applications do very, very slow (e.g. playback mp3, slow start and interrupted sound).

- rt2800usb crashes when the memory allocation model is SLAB. Under SLUB it performs more stable, but after 5-20 Minutes iperf testing, a nullpointer crash may occur. Very interesting aspect: with comparable transfer speeds (approx. 17 Mbits/sec with 54Mbps wifi speed) as in the atheros case, other apps do not slow down significantly (e.g. mp3 playback without any problems). Apparently, buffering design in rt2800 is better or simply eats less CPU.


In general, the throughput is good only when voluntary kernel preemption is active, not in "preemptive Kernel", regardless with of the three associated suboptions is used. Then throughput can be considerably slower, especially with rt2800.


Linux version: ADI-2011R1