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Wireless problems - Slow speeds

Posted: Tue Jan 11, 2005 8:04 pm
by wildbill442
Our company just decided to switch from Proxim Orinoco AP's to Mikrotik based AP's. Ever since doing the upgrade at our main tower our customers have been reporting extremely slow speeds. There doesn't seem to be any corilation in their geographic locations or the APs they are connected to..

First off.. I'll start with the tower design.

One omni antenna at the top > 1WATT AMP > 300' LMR1200 > DC Injector > Mikrotik (Prism 200mW)

One 90 degree Sector > 1 WATT AMP > 300' LMR1200 > DC Injector > Mikrotik (Prism 200mW)

Mikrotik config:

RouterOS V. 2.8.22 - current
1.8ghz Pentium (3 or 4)
512MB RAM
Routerboard 14 (4 miniPCI to PCI)
2 x PRISM 802.11b 200mW
1 x Atheros 802.11a/b/g 100mW (currently not being used)

Customers are getting good signal's but they are continuously reporting horrible speeds. 200kbps - 400kbps... Uploads are even worse 60-90kbps peaking at 400kbps (very rare)..

This was all working until we swtiched over to the Mikrotik solution. We were hoping we could get more bandwidth and users switching to the mikrotik platform, but so far all we have is more truck rolls and headaches.
1  R name="*****1" mtu=1500 mac-address=00:02:6F:06:A4:D6 arp=enabled 
      disable-running-check=no interface-type=Prism prism-cardtype=200mW 
      radio-name="00026F06A4D6" mode=ap-bridge ssid="ssid1" frequency=2452 
      band=2.4ghz-b scan-list=default-ism rate-set=default 
      supported-rates-b=1Mbps,2Mbps,5.5Mbps,11Mbps supported-rates-a/g="" 
      basic-rates-b=1Mbps basic-rates-a/g="" max-station-count=2007 
      tx-power=default periodic-calibration=default fast-frames=yes 
      dfs-mode=none antenna-mode=ant-a wds-mode=disabled 
      wds-default-bridge=none wds-ignore-ssid=no 
      update-stats-interval=disabled default-authentication=yes 
      default-forwarding=yes hide-ssid=no 802.1x-mode=none 
      disconnect-timeout=3s on-fail-retry-time=100ms 

 2  R name="******2" mtu=1500 mac-address=00:02:6F:30:F5:59 arp=enabled 
      disable-running-check=no interface-type=Prism prism-cardtype=200mW 
      radio-name="00026F30F559" mode=ap-bridge ssid="ssid2" frequency=2422 
      band=2.4ghz-b scan-list=default-ism rate-set=default 
      supported-rates-b=1Mbps,2Mbps,5.5Mbps,11Mbps supported-rates-a/g="" 
      basic-rates-b=1Mbps basic-rates-a/g="" max-station-count=2007 
      tx-power=default periodic-calibration=default fast-frames=yes 
      dfs-mode=none antenna-mode=ant-a wds-mode=disabled 
      wds-default-bridge=none wds-ignore-ssid=no 
      update-stats-interval=disabled default-authentication=no 
      default-forwarding=yes hide-ssid=no 802.1x-mode=none 
      disconnect-timeout=3s on-fail-retry-time=100ms 
Also am I right in thinking that I needed to create a bridge interface and add the interfaces needed to pass traffic between them? So like say i have 4 interfaces, 2 wireless, 1 WAN, 1 LAN. Would all these interfaces need to be on the same bridge in order to pass traffic between them?

well this i how its setup so if I'm wrong please correct me:
 0 management       none    128      10       
 1 internal         bridge1 128      10       
 2 external         bridge1 128      10       
 3 ether5           none    128      10       
 4 ether6           none    128      10       
 5 atheros          none    128      10       
 6 f***1             bridge1 128      10       
 7 f***2             bridge1 128      10 
Any and all help is greatly appreciated!

Posted: Tue Jan 11, 2005 8:08 pm
by stephenpatrick
If you bridge both radio cards you get the traffic from one retransmitted on the other .. will cause throughput to decrease drastically.
Need to set this up differently, bridging the wireless interfaces together is a "no-no" as far as I can see

Regards

Stephen

Posted: Tue Jan 11, 2005 8:13 pm
by wildbill442
Oh I forgot to mention we have about 20 users off of the omni, and probably another 20 off the sector. At least thats all that is showing up as connected...

Posted: Tue Jan 11, 2005 8:18 pm
by wildbill442
If you bridge both radio cards you get the traffic from one retransmitted on the other .. will cause throughput to decrease drastically.
Need to set this up differently, bridging the wireless interfaces together is a "no-no" as far as I can see

Regards

Stephen
Then how do you get traffic to flow from the wireless interfaces to the ethernet? If i remove it from the bridge traffic goes nowhere..

I don't see how this could be the problem, this would be just like plugging two AP's into the same switch.. Unless my understanding of a bridge is incorrect.

Posted: Tue Jan 11, 2005 11:41 pm
by wildbill442
Anyone? My subs can't hit speeds of anything over 1mbps download and they're lucky to sustain that. The uploads are even worse 500kbps at most 60kbps is more the norm...

Posted: Wed Jan 12, 2005 6:04 am
by jarosoup
FYI, running those antennas on a 1 watt amp (especially a sector!) is quite illegal in California (you can have no more than a 6dBi antenna on 1 Watt). They could be causing you problems too. Unless your customers have amps on their end too, you aren't gaining much anyway.

Edit: Sorry, didn't notice the length of cable there. But as you describe it, those amps are right on the antennas (?) instead of at the other end...

Re: Wireless problems - Slow speeds

Posted: Wed Jan 12, 2005 9:49 am
by mag
was the system not testet before put into service? or did it work with a few test-clients?
the AP hardware looks good to me, but i'm not sure abbout the prism interfaces, as we're using atheros only.
there are some questions left open to me:
is the AP intended to work as transparent bridge? external and internal interfaces are in the same bridge group.

how do the customers get their ip-addresses, i.e. how is internet connectivity structured?

if the whole AP is configured as a bridge, to what device is it connected? perhaps another bridge?
If you bridge both radio cards you get the traffic from one retransmitted on the other .. will cause throughput to decrease drastically.
Need to set this up differently, bridging the wireless interfaces together is a "no-no" as far as I can see
is that true even if "default forward=no" has been set?
by now we're putting all access-interfaces on a particular AP (<30 users per interface) into a bridge group and didn't see disadvantages so far.

regards.
  matthias

Posted: Wed Jan 12, 2005 11:33 am
by tully
The Proxim radio has 65mW of output I think (maybe 35mW). If the amp and cabling were set up for that to work, then you may be better off powering down the Prism cards to something like 65mW -- test using a bandwidth tester and different power levels. If the amp has AGC, then maybe it is ok.

If the two prism cards are sittting next to each other in the RB14, then they can interfere with each other even when on different channels -- the radios are rather noisy. You may be able to move one radio to the other side of the RB14 and get better isolation. The Atheros radios are not noisy, so it may be better to use two of those for this setup.

Like the other forum members said, bridging all the traffic and other configs could be causing problems.

John

Posted: Wed Jan 12, 2005 6:49 pm
by wildbill442
Network Config is as follows


Internet > Cisco Router > NetEnforcer (bandwdith shaping) > Mikrotik (AP's, firewalling) > Dell Switch

All customers have Static IPs.

The AMP is at the top of the tower closest to the Antenna if we were to amplify at the bottom we'd be amplifying extremely weak signals due to the loss of the LMR. And we aren't doing any ampilfication on the CPE side. All Zcomax 250HP (4200mW).

Proxim radios are set at 200mW I have extra Atheros cards so switching them out is a possibility and I might try lowering the tx-power.

The system was working great prior to the mikrotik switch over. And the mikrotik setup was tested in a lab but to no great extent. I don't believe we did any bandwidth testing.

Posted: Wed Jan 12, 2005 10:35 pm
by msolis
Don´t use amplifiers. Use Routerboard 230 outdoor (http://www.routerboard.com). This solve your lost signal problem without causing noise. I have Ap´s with client to 12 Km, 3 Mbps (TCP). 15 dBi Omni in AP and 24 dBi grilla in the client. Of course, my AP does not have amplifier and is above in the tower.

Posted: Wed Jan 12, 2005 11:09 pm
by jarosoup
If anything, your amps should be at the bottom of the tower. LMR1200 has about 2dB of loss per 100 feet. If you sector is a 13dB, you're broadcasting upwards of 20 Watts. Putting your amp at the bottom would put you right near the 4 Watts allowed. You should really look into part 15 of the FCC rules.

If you're running on noisy channels, using amps will only make this worse as it amplifies the noise too...plus, the radios you have have a very high receive sensitivity and will see this noise "better". Try your links without the amps.

Posted: Thu Jan 13, 2005 2:47 am
by wildbill442
Yeah I think the AMPs are the problem.. after doing some math i figure we're pushing about 55dB through our antenna there which is close to 400Watts... correct me if I'm wrong

Radios = 100mW
AMP = 1Watt
Antenna = 12dBi

100mW = 20dB
1 Watt = 30dB
Antenna Gain = 12dB
Cable loss = ~7dB (LMR1200 every 100' = -2.26dB)

total output power 20dB + 30dB + 12dB - 7dB = ~55dB = HIGH WATTAGE!

Someone please correct me if my math/conversions are wrong..

Unfortuneately we didn't build this network from the ground up, but bought it off a company that already had it in place and never went through the whole tower design. Since the loss is so low through the LMR1200 we're just going to take the amplifers out and hopefully that will correct our bandwidth issues and when we redesign the tower we'll definately do it right, cat5 up to a few routerboard 230's with 4 90 degree sectors and as little LMR as possible! I'll post the updates when we're able to get a tower climber to scale it.

Thanks for the input, oh and jarosoup it is NEVER recommended to amplify at the bottom of a tower. All of the RF seminars I've been to have always recommended putting the amps as close to the antenna's as possible otherwise all your amplification is lost in the attenuation of the cable. And I'm sure there were some other reasons I don't recall.

Posted: Thu Jan 13, 2005 12:19 pm
by [ASM]
20dB + 30dB
I think that's wrong. The real output power is 30dB (in best case).

Posted: Thu Jan 13, 2005 1:13 pm
by stephenpatrick
That's EIRP he's getting by including the antenna gain, not total radiated power I think.

Posted: Thu Jan 13, 2005 6:59 pm
by jarosoup
Actually, it would be Amp (30dB) + Antenna (12dB) - Cable & Connector Loss (3dB) = 39dB which is really only 3dB over the limit and about 8 Watts. The 3dB is really only an estimate but you'll lose some power just going through to N-connectors and a pigtail. Since the amp is at the antenna, there is no 300 feet of cable loss, and you don't combine the radio power as it is "lost" once is goes into the amp. It's not as bad as I initially thought. I'd still bet you'd have better luck without the amp.

Posted: Fri Jan 14, 2005 9:42 pm
by wildbill442
Looks like its fixed! We switched from the Engenius 200mW Prism based miniPCI cards to the Atheros AR5213's and now everything running great, users reporting 3mbps down and well over 1mbps UP.


EDIT::

CPU Utilization is also quite a bit lower with the Atheros cards than with the Prisms. Prisms were causing 20-50% CPU usage, where the Atheros cards are only using 1-10%. I don't think I'm every going to touch that prism chipset again...

Posted: Sun Jan 16, 2005 9:46 pm
by marksx
try to enable "fast-frames" option
this will give speed UP on prism cards :-)

Posted: Tue Jan 18, 2005 9:28 pm
by Trisc
If the two prism cards are sittting next to each other in the RB14, then they can interfere with each other even when on different channels -- the radios are rather noisy.
Now you tell us! Does disabling one of the cards remove all interference?

TC

Posted: Wed Jan 19, 2005 9:18 pm
by mperdue
When using the Prisim 200mw cards and an AMP you need to lower the wattach on the Prisim to 30mw or 100mw. The 200mw card will over power the input side of the amp.

Amp's have a min and maxium input power, going over that will cause problems.