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overloaded

Posted: Thu Feb 23, 2006 11:40 am
by YappaDappa
Hey guys. I have what I suspect to be an overloaded sector. I am running a routerboard230 with 1 200mw prism card with latest firmware + 1watt amp. I have 3Mbit of bandwidth to share with clients. I have 45 users. Performance stinks. VERY inconsistant. I suspect this card is over stressed. How can I relieve some of the stress to the card, or what do you advise I replace it with. I am using a single 15db 120 sector antenna at this particular spot. I have al users rate limited to 256kb. I removed bursting, and things improved a bit. I applied P2P Queue, and set firewall rules for added security.

Posted: Thu Feb 23, 2006 4:24 pm
by bushy
Maybe replace the single sector with two or three antennas and share the clients between them.

Posted: Thu Feb 23, 2006 4:45 pm
by macgaiver
Check user-user traffic - disable default-forwarding option!

Posted: Thu Feb 23, 2006 5:01 pm
by NetTraptor
45 users waaaaaay to many for an AP... it's not only the data bandwidth and traffic... it has to do with radio... 10-15 people permanetly connected might be OK on an Interface and this only when they respect your AP... low tx power settings, directional antennas so on and so forth...

Try more interfaces... you will give a bit of space and time for your Interface to breath... Then use traffic shapping on each Interface so that leachers do not copletely suck all your bandwidth :wink:

Posted: Thu Feb 23, 2006 8:52 pm
by mikapojic
I would have to confirm that there are too much users on your ap try with 3 sector antenas with 3 prism`s. We have that kind of system with SR2 instead of prism and it rock`s. We have 140 user per base station and pings are 2-7 ms.

Posted: Fri Feb 24, 2006 5:07 am
by YappaDappa
Hi.

140 users/3 sectors =~47 users per AP. I have 45

So, you are not overloaded?

Posted: Fri Feb 24, 2006 10:41 am
by HarvSki
YappaDappa

What RTS / CTS do you have set on the CPEs?

Thanks
Harvey

Posted: Fri Feb 24, 2006 10:52 am
by YappaDappa
I am using senao CB3+ for CPE. I always set rate to "1,2Mb"

Posted: Fri Feb 24, 2006 11:39 am
by mikapojic
thing is "per sector" not on omni, we have tested it on omni and we could get as fa as 20 users working properly on that interface. We setup omni antena first then when neaded we setup 3 x sector interfaces and boost our bandwidth.

Posted: Fri Feb 24, 2006 9:39 pm
by eflanery
I am using senao CB3+ for CPE. I always set rate to "1,2Mb"
Ouch, why would you do that?

By forcing things down to the lower modulations, you may be able to get a bit more distance, and opperate with less SNR, but only at an extremely heavy capacity cost.

Under 802.11b, we used to allow automatic rate selection, but by doing so, we limited ourselves to ~30 clients per AP. Now we always lock it down to 11Mbps fixed, and some of these APs now easily support 100+ clients. If the client cannot maintain a stable connection at 11Mbps, then they need to buy a more powerful radio, better antenna, or entirely different system. If those are not options, we won't sign them up.

Also, that isn't an answer to the RTS/CTS question.

--Eric

Posted: Sat Feb 25, 2006 1:00 am
by YappaDappa
interesting. we locked down to 1,2 for two reasons. One, it seems to work well as a built in rate limiter. Two, when we set to 11, pings sometimes go haywire, and in some cases >2miles, we start to see reregistrations. Does that make sense to you?

Frag thresh: 2346
RTS: 2432

Posted: Tue Feb 28, 2006 1:24 pm
by HarvSki
I've been setting RTS/CTS (fragmentation) on all client devices on a test AP to 512, so far things are looking OK, apparently this will help with the hidden node problem and allow a larger number of clients per AP before things start to fall appart.

Unfortunatley the MT does not seem to have an option for RTS/CTS.... my crappy Dlinks do though :) So I guess the only option is to build an MT only network using nstream and polling, which is probably better but not WiFi

Posted: Tue Feb 28, 2006 11:48 pm
by eflanery
interesting. we locked down to 1,2 for two reasons. One, it seems to work well as a built in rate limiter. Two, when we set to 11, pings sometimes go haywire, and in some cases >2miles, we start to see reregistrations. Does that make sense to you?

Frag thresh: 2346
RTS: 2432
It works as a rate limiter, since you are making every byte take 5.5-11 times as much spectrum-time. It's much better to rate-limit at a higher layer, since you would now be freeing up the extra spectrum-time.

I.e.: (oversimplification)

At a 1Mbps rate, you can move at most 1Mbit in 1second. The channel is ocupied for the entire second, though. Nothing else can be done.

At a 11Mbps rate, that same 1Mbit only occupies the channel 1/11th of a second. Leaving the remaining 10/11ths for other data.

As for the funky pings, and re-registrations, yes it makes sense. It is more difficult to get a stable 11Mbps signal, than it is to get a stable 1Mbps signal (which is why they put the option in the 802.11 spec to begin with). Essentially, this works out to a SNR requirement, 11Mbps needs a better SNR than 1Mbps does.

Unfortunately, like amps, low modulations can be difficult to get rid of, even when they are crippling your network. If you install a customer, who works fine with a 1Mbps signal (and a sub 15 SNR, or so), there is a good chance that customer will not be stable at 11Mbps, without a CPE replacement and/or upgrade.

We used to allow the system to select it's own data rate, but that did nothing but cause trouble. For the last couple of years, we have been locking everyone on 802.11b to 11Mbps, and the APs where everything is purely 11Mbps perform MUCH better (some have more than 100 customers on them, with very few problems). We have been reworking the old systems, and at this point we have probably replaced 300 CPEs due to this.

Once an AP has been locked down, we can commonly get 5 times as many customers on it as before, and see a significant reduction in complaints.

We will no longer take a customer on 802.11b if they cannot sustain a stable 11Mbps signal, the damage they would do to the network far outweighs any benefit of having them as a customer. If a customer has already been installed, and already has the best 802.11b radio/antenna combo; then we refund their installation cost, reclaim the gear, say sorry, and try to get them on another system (Polling wireless, DSL, FR, etc...). Somtimes we just have to give up on the customer entirely, but it's better to lose one customer, than it is to have fifty angry ones.

--Eric

thanks

Posted: Wed Mar 01, 2006 2:05 am
by YappaDappa
Great explanation. Thanks for taking the time.

I will try your recomendation on one sector, and see how things go.

Posted: Wed Mar 01, 2006 2:11 pm
by ofasa
How do you 'lock' the clients to 11 Mbps? At the AP?

Thanks.

Posted: Wed Mar 01, 2006 2:18 pm
by cmit
By setting the basic-rate and supported-rates to 11 MBit/s at the AP. Then only clients able to maintain a 11 MBit/s connection can connect...

Best regards,
Christian Meis

Posted: Wed Mar 01, 2006 2:19 pm
by normis
this means that most clients will not be able to connect

Posted: Wed Mar 01, 2006 2:24 pm
by cmit
"Most" is an arguable value ;)

In the course of Eric's description above I just explained how to do it. You are of course locking out many possible clients that could get a connection at lower air rates.
But the advantage you are gaining as explained by Eric surely is worth being considered at least. I have done this in a few occasions, too.

But the decision to do so should be an individual one and only be made if you (i.e. the person doing it that way) are clearly aware of what the effects of this are. It's a balance between limiting your possible client base and trying to guarantee a certain quality of service.

For a public hotspot, for example, I would consider this a bad idea. The situation when connection "fixed wireless" clients is a completely different one...

Best regards,
Christian Meis

Posted: Wed Mar 01, 2006 6:49 pm
by YappaDappa
alot to consider. Of course, nothing says I won't benefit from locking to 5.5, which, according to this information, is still going to be way better than my locked down speeds of 1 or 2Mbit. Should be interesting. I'll post the results from my first sector soon. Thanks all.

Posted: Wed Mar 01, 2006 8:30 pm
by eflanery
By setting the basic-rate and supported-rates to 11 MBit/s at the AP. Then only clients able to maintain a 11 MBit/s connection can connect...

Best regards,
Christian Meis
In addition to doing it at the AP, we also set the CPEs up for 11-fixed only.

--Eric

Posted: Wed Mar 01, 2006 9:10 pm
by eflanery
It's really a judgment call, depending upon your intentions for the system.

If ease of connection is your goal, such as it would be with a hotspot, auto rate selection is porbably the right answer. Locking it down would be a support nightmere.

If the goal is stability and capacity, such as with a fixed PtMP system, we have found that locking the data rate down is essential.

It's not easy. We do turn down many customers that we _could_ make work; it's tough to say no, when you _could_ say yes. In our case, we usually don't lose the customer, they just end up on a lower margin system, like DSL, ATM, polling Wireless, etc.... But we do lose some, and without the other options we have, we would likely lose many more.

Also, dependancy on low data rates (just like dependancy on amps), can be a painful habit to break. Replacing large numbers of CPEs, and forcing some existing customers off the system entirely, can be costly, and is never plesant.

--Eric