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Adam McLaughlin
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What limits the overall channel throughput when serving clie

Thu Oct 25, 2007 8:45 am

Hey Everyone,

I am noticing a bizarre problem with our MikroTik gear that I can't seem to nail down.. So I am hoping that someone here can suggest something for me to check to fix this.

Problem here is that I can't seem to get above about 1.5 mbps on the channel while serving clients. Can't figure out why, either.

CCQ on the channel hovers between 90 and 100 for the Access Point. There are about 19 clients on this channel. 1/3 of them are RB133C and R52H, and the rest are Engenius CB3 or CB5. Signal levels from the clients in are between -67 and -75.

The Access Point is a RB532 w/ a R52 in it.

What limits the on air traffic between the clients?

Theoretically if the A.P. is running at CCQ of nearly 100%, wouldn't the channel capability be something like 5-ish Mbps??

Working in B mode, with standard 20 Mhz wide bandwidth.

What could be wrong here? Is it the Queue type for the wireless interface? I'm all out of ideas.

Adam
 
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roadrunner
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Re: What limits the overall channel throughput when serving clie

Fri Oct 26, 2007 8:50 am

What rates are the clients operatiing at? 5.5/11 or 36/48/54? Is anything set to 2.4 b/g, or just 2.4b?
You mentioned only 1.5 Mbps, what is the packet rate (pps)?
If you have a client with a worm or virus infection that is sending out a large number of small packets, it could lower your speed capacity. If that client is only connecting at a slower speed, then the problem is even worse. The client will take up more 'airtime' when sending traffic.
Try to get your busiest users at the highest connection rate, 48 or 54Mbps if possible.
You have 90-100 CCQ at the ap, but on your rb133/c clients, what is the CCQ on their end?
Also, make sure that you don't have too many filter rules that are slowing down the AP.


I just checked out the specifcations for the CB3 & CB5, they seem to be 2.4 b only. Set your AP and your rb133/c clients to be 2.4 b/g. This will let those clients 'burst' a little faster. With almost 20 clients running 2.4b 1.5 doesn't seem that bad. All the broadcast, multicast and beacon traffic is transfering at the 1Mbps data rate. 802.11b running at 11Mpbs only has a max speed of around 4-5Mbps in one direction.
 
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Adam McLaughlin
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Re: What limits the overall channel throughput when serving clie

Fri Oct 26, 2007 9:00 am

Thank you for the reply!! I could use all of the heads I could in tracking down this problem.

Please allow me to address your questions as they are presented:

A. Everything here is just 2.4b mode. The clients are working at 11 mbps when I see this low ceiling.
I believe that I am married to the B mode, as I have channel specific filters on the antennas coming in to the Access Points here. Can't go to G for the extra wide bandwidth required there.

I will have to look at the packet rate when under load and see what it suggests.

When I see a CCQ rate of say 98%, I also see that CCQ rate at the client end as well; the numbers do match.

There are no filter rules, no nat, no mangle, nothing on the A.P.

And I am still at a loss why the thing caps out so early. I have one client on, pulling down 500k, and then I do a BTest to someone else, and I can't get another 500k to that guy. In this instance, it capped out at just under 1 mbps... And there were only two clients on at that time.

It is a real head scratcher.

Adam
 
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Re: What limits the overall channel throughput when serving clie

Fri Oct 26, 2007 9:14 am

I thought that 802.11g had the same 22 mhz channels, G-Turbo has the wider 40Mhz channels.

While using 802.11b for a Point to Point link I have seen speeds up to 3-4 Mbps. But for an AP with multiple users, 2.5 Mpbs might be the most you ever see.
 
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Re: What limits the overall channel throughput when serving clie

Fri Oct 26, 2007 9:26 am

In standard B mode, I can get around 5 megs of TCP throughput using fairly low-end equipment (an RB133c with a CM9 for the AP and a linksys router for the client)
 
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Adam McLaughlin
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Re: What limits the overall channel throughput when serving clie

Fri Oct 26, 2007 9:31 am

You know what - after I posted that I started to look the bandwidth of the channels up myself. I even doubted that as I typed it! :-)

I have a point to point link running seven miles between one tower and another out here. This operated in 802.11B. I can see 5.4 to 5.3 mbps on BTest, but then again the signal levels are something like -56 or so on both sides.

I have a friend on this board whom can sell 1 mbps, 2mbps, 3 mbps on 802.11B to CB3s and Rb/133Cs without an issue, and he does this with sixty clients registered to the A.P.!!

But he doesn't have this bizarre 1.5 mbps channel limit when the A.P. is addressing as few as 2 or 3 clients.

I will try an experiment, just to see what would happen. I'll set the A.P. to go to B/G mode, and wait for the channel to become busy. As soon as it does, I will run BTest to some other clients "wide open" and see what the channel throughput is like. I know that theoretically this shouldn't make a difference, but I have found stranger "solutions" in very obscure areas with RouterOS.

Adam
 
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Re: What limits the overall channel throughput when serving clie

Fri Oct 26, 2007 9:36 am

One more thing to check out would be the cpu utilization. I do notice that when a customer uses a P2P program, the sheer number of connections slows the boards down.

Something could be enabled which causes the cpu to spike and limit bandwidth. Connection tracking tends to slow things down. From my experience, Nstream made my cpu idle at about 50% even when no bandwidth was being used.
 
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Adam McLaughlin
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Re: What limits the overall channel throughput when serving clie

Fri Oct 26, 2007 9:48 am

CPU utilization seems to idle at less than 10% on the A.P. The A.P. is a RB532 w. R52 in it. Pretty simple. Does nothing but work as an A.P.

This is making me tear my hair out, and really limiting growth....

Adam

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