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mrb
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Four APs vs two APs over bridge

Thu Feb 28, 2013 11:46 pm

I have 4 RB951-2n devices, all running ROS 5.24.

Area I want to cover is an office in an apartment building. There are many APs (both weak and strong) in the building, using various channels, and I suspect they are mostly set to "auto" channel (so the term "least used frequency" is of little relevance here, I think).

Since our office is small, you might wonder why I have 4 APs. It's a fair question: we have 20+ wireless devices, most of which are transferring data at any given moment.

This is the layout of the office (pardon my humble drawing skills):

Image

Red triangle is where router and rest of network equipment is located. I've tried to represent relative signal strength around the office: green would be "full" signal, in orange area it drops to around 2 bars. I know it's not exact, but it's just to get the idea of signal how signal spreads in our office.

It is not possible to pull cables around, so what do you think, which of following two configurations make more sense?

1. 4 APs connected directly to a router, all placed where red triangle is, configured with same SSID/security settings, but on separate channels (1,5,9,13), so that clients connect to any of these four, thus sharing the load.

2. placing AP1 where "router" is, and AP2 at "location 2" (see image). Both APs share SSID and channel number (or perhaps they should operate on separate channels, too?). AP1 and router are connected via cable. AP2 and router are connected via AP3+client bridge (AP3 is on the router side, client is on AP2 side) which operates on separate channel with separate SSID naturally, and acts as a bridge. This configuration should (at least in theory) allow clients in closer proximity to either AP1 or AP2 to connect to them, thus sharing the load between two APs, while bridge would not be impeded by clients, so it should have best performances possible.

Any thoughts?
 
0ldman
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Re: Four APs vs two APs over bridge

Fri Mar 01, 2013 1:29 am

The repeater idea might work, using 5GHz for the bridge.
 
mrb
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Re: Four APs vs two APs over bridge

Fri Mar 01, 2013 1:51 am

Sadly, I don't have 5GHz equipment. I was thinking of operating bridge on channel 13, as apparently every wireless device comes uses channels 1-11 (unless configured otherwise). But then, I'm thinking if channels 1 and 6 could be used for AP1 and AP2..?
 
MacLean
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Re: Four APs vs two APs over bridge

Fri Mar 01, 2013 8:49 am

If the area is pretty saturated with 2.4 GHz I would suggest using horizontal polarization on your antennas and see what your signal strength is before adding APs.

-Mac
 
0ldman
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Re: Four APs vs two APs over bridge

Fri Mar 01, 2013 7:49 pm

As I see it you can get some 5GHz equipment or you can deal with 2.4GHz not doing the trick.

This is the same location as your posts about the mesh problem, right?
 
mrb
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Re: Four APs vs two APs over bridge

Fri Mar 01, 2013 8:33 pm

@0ldman: Right.

I've tried bridge over ch13 and ch11, but it doesn't yield satisfactory results. Bridge starts failing as soon as some traffic is generated through AP2, and by some traffic I mean total of 1-2 Mbps (it peaks to 5 Mbps if I recall correctly). Ping goes on fine, 3-4ms for about 10-20 seconds, then jumps to a few hundred (300-700ms) for another 10 seconds, and then timeouts (so it is 1000+ ms) for about half a minute, and starts all over again. Not to mention that everything just stops working from AP2 side. Intervals are irregular, too, so it's not that exact as I describe.

So I tore down the bridge, and put 3 AP's next to each other, lowered output power (about 2.5 mW, but it still covers entire office with "full bars"), put them on ch1,6,11 and let it be for the time being, setting separate SSID on each. I've asked office coworkers to split themselves between the APs. But then something unexpected happened. I've expected that unused APs on different channels would work perfectly for up to 10 stations, but as soon as 2-3 stations connected, packets and connections started dropping, unable to surf the net properly.

I've been looking at registration table, and I've noticed that tx hw frames surpass tx frames more than twice in some of registered stations. Any ideas why it might be? Picture below shows some of what I'm talking about - now everybody has left the office so there's not enough stations to show what I'm talking about, but it's much worse with more stations.

Image

As I'm not very experienced in building indoor wifi networks, I don't have a solid ground on what properly configured wifi network looks like, but I don't think it should look like this...

Would it do any good if I limited max-station-count to 8 on each AP, put back same SSID on all 3 APs and let them balance themselves out?
 
mrb
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Re: Four APs vs two APs over bridge

Mon Mar 04, 2013 8:47 pm

It turns out that from time to time, something happens with bridge on all APs and it becomes unreachable for a moment.

When that happens, all wifi clients are still connected to AP, but they loose connectivity to network. After bridge returns, renew their DHCP leases. If winbox connection happens to be open to said AP via IP address, it is dropped as well.

AP network config is like this:
/interface bridge
add name=bridge1 disabled=no l2mtu=1600 mtu=1500 protocol-mode=none
/interface bridge port
add bridge=bridge1 disabled=no interface=ether1 path-cost=10 priority=0x80
add bridge=bridge1 disabled=no interface=ether2 path-cost=10 priority=0x80
add bridge=bridge1 disabled=no interface=wlan1 path-cost=20 priority=0x40

/ip address
add address=192.168.1.11/24 disabled=no interface=bridge1 network=192.168.1.0
add address=10.1.1.1/24 disabled=no interface=wlan1 network=10.1.1.0

/interface wireless
set 0 band=2ghz-b/g/n bridge-mode=enabled channel-width=20/40mhz-ht-above \
    default-authentication=yes default-forwarding=yes disabled=no \
    frequency=2412 hide-ssid=no l2mtu=2290 mac-address=D4:CA:6D:xx:xx:xx mode=ap-bridge \
    mtu=1500 name=wlan1 radio-name=AP1 security-profile=default ssid=BuggyNet \
    wds-mode=disabled wireless-protocol=802.11 wmm-support=disabled
# i'm not running an open hotspot, despite of security-profile=default :)
Any suggestions?

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