Re: Dual band

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On 01/05/2018 03:09 PM, Matthias May wrote:
On 05/01/18 21:19, Fejes József wrote:

Yes this allows you to create 4 APs, but on the same frequency.
The key here is not that you can create 4 APs, but the "channels <= 1", meaning the card can only operate on a single
frequency.
Dual Band usually means the card can operate on 2.4Ghz and 5Ghz, but not at the same time.

I'm not aware of "any" card which supports multiple frequencies at the same time, not only from software side, but
mainly from hardware side.
How would this work? How would you isolate multiple transceivers transmitting at the same time?

Scenario:
Put 2 different cards into a single device, and put terminators on one, and a power meter on the other:
When the card with terminators transmits something, you will still see the signal with ~20dB attenuation on the other card.

BR
Matthias

The Asus RT-AC88U router is very similar to the Asus PCE-AC88 card:
both contain a single BCM4366 chip (they definitely run with the same
chip firmware). The router can definitely operate in simultaneous dual
band mode (one channel in the 2.4GHz band and another channel in the
5GHz band). The antenna and MIMO configuration also hints at this
capability. Except the router runs Broadcom's proprietary wl, not
hostapd.

Anyway, this part is obsolete for me, as I got a PCE-AC88 for testing,
but it physically didn't fit in the enclosure of the HP microserver.
We'll never know if it would have worked or not, my guess is 50-50. My
plan B is two separate cards in a Mikrotik RB14e so problem solved.

However, the following still stands: it would be nice if hostapd could
create and destroy virtual interfaces on demand. It would be somewhat
similar that I don't have to put the card into AP mode with the iw
command, hostapd does it for me, and I could create virtual interfaces
with iw but hostapd could do that too. Then I could run one instance
of hostapd with two configs, and both configs could reference the same
physical interface. It's nicer than setting up the virtual interfaces
by hand and ensuring it happens before hostapd starts.



If you look at the specification of the Asus AP you reference, you will
see that this AP uses internally 2 different cards (See [1]).
When you run a test on this AP where you actually try to use both bands
at 100% you will notice that the two cards interfere with each other.
You will get 100% airtime, but a lot of corrupt frames on both bands.

Regarding your other question:
You can't run multiple hostapd instances on the same physical interface.
What you can do is create multiple virtual interfaces with iw on the
same physical interface which share the hardware (thus the configured
frequency).
Please read the hostapd.conf example at [2]
Look for the section labeled "Multiple BSSID support"
In such a setup you have a single configuration for a single hostapd
instance but with multiple bssid sections.

You can also create multiple virtual interfaces on a single radio, and run a hostapd instance
on each.  You do have to be a bit careful about how you configure things,
and might need to hack hostapd in order to force it to not switch primary/secondary
channels in case where one vdev is HT20 AP and the other is VHT80, for instance.

I am guessing the approach you describe and my approach are effectively
the same in the end...I just find my way easier to support for my particular
application.

Thanks,
Ben



--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc  http://www.candelatech.com


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