Hi, Yes. There's nothing really stopping you from doing this. You can just associate in both directions and then only send data out one link.
Now, having the nic be _transmit only_ and the other nic be _receive only_ is a little tricky, as there's a bunch of 802.11 negotiation stuff that's going on that really assumes it's happening on a single VAP. The net80211 code could be hacked to transmit things out a different device - ie, one VAP has a transmit device and a receive device. You'd have to turn off things like hardware ACK, hardware RTS/CTS, etc. But it's doable. -a On 21 May 2014 11:39, Richard Yao <[email protected]> wrote: > Dear Everyone, > > I recently read about Ubiquiti’s AirFiber hardware and noticed that its link > efficiency is remarkable. Air Fiber’s link speed is about 770Mbps up and > 770Mbps down (a 1:1 split). People are reporting benchmarks that show 700Mbps > throughput over miles. The link efficiency is therefore in the range of wired > ethernet, which typically obtains iperf results in the range of 85% to 95%. > So far, all benchmarks of WiFi that I have seen never touch 1/e or roughly > 37% efficiency. A few have come rather close to 1/e though. > > The 1/e number is significant because I am told that it is the theoretical > limit on the efficiency of wired ethernet when a there is a shared collision > domain on a coaxial cable. After reading about how the Air Fiber hardware > works, I hav suspicion that its link efficiency can be replicated between two > computers with off the shelf Wi-Fi hardware by abusing the radios via the > kernel driver. In specific, you would have two systems, each with two radios > on different frequencies. I will call each system A and B and refer to their > radios as indices into an array. e.g. A[0] and B[1]. > > Much like the AirFiber, I envision node A as having A[0] be transmit-only on > the frequency that B[0] uses (frequency 0) with B[0] being receive only. > Similarly, I envision node B as having B[1] be transmit-only on the frequency > that A[1] uses (frequency 1) with A[1] be receive only. The kernel driver is > to instruct the WiFi hardware to ignore everything about the 802.11 protocol > possible (e.g. RTS is to be ignored), send frames when given a packet (in > send mode) and receive forward frames when hearing a packet (in receive > mode). No radio in send mode is to listen to packets and no radio in listen > mode is to send packets. The radios would be attached to directional antennas > and frequency 0 != frequency 1. > > I asked Adrian Chadd about this in IRC. He replied that it is possible to > hack the driver to obtain tight control over when 802.11 frames are > received/sent, but doing something like this would require oscillator > isolation and baseband RF isolation. He also asked that I send my question to > the list, so here it is. > > How doable is this with off the shelf hardware? Could simultaneous dual-band > equipment be abused to obtain the proper isolation (where 2.4GHz is 1 > direction and 5GHz is another)? Would it be reasonable to expect wireless > throughput to achieve 90% of the link speed in this configuration? > > Yours truly, > Richard Yao > > P.S. I am not on the mailing list, so please include me on CC. > _______________________________________________ > [email protected] mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-wireless > To unsubscribe, send any mail to "[email protected]" _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-wireless To unsubscribe, send any mail to "[email protected]"
