I have the 2.4 PMP 450 AP's and SM's. I have a couple AP's with about 40 registered SM's and we are getting complaints of slow speeds. Is it possible that these AP's are overloaded? And is there anything I can do short of adding AP's or kicking customers off the network to try and resolve this issue?
There are many statistics available on the PMP 450 system that can help you determine what's going on with your network. Maybe the most important ones to look at first are the frame utilization statistics on the AP.
If this number is at or around 100% most of the time, then yes, you're out of capacity at the AP, and would need to add additional APs to provide more.
You may also want to consider limiting the amount of throughput the customers are able to use by establishing bandwidth profiles using MIR levels in each SM.
Do you have any network monitoring currently? Keep in mind that all PMP 450 equipment has complete MIBs with OIDs for nearly everything, that can be polled via SNMP at regular intervals to help you monitor what's going on.
We also offer Wireless Manager (and soon cnMaestro) to help with this.
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+1 frame utilization. And throughput monitoring.
If frame utilization is high but the throughput statistics doesn't look like you're getting all of the speed that you expect, look at the session list. Specifically the power tab. If you see some (or a lot) of sessions at 8X/1X, 2X or even 4X (this is the downlink rate to the SM), then those weak or noisy SM links are going to degrade your overall sector capacity if they are actively passing traffic. You can also have MIMO-A (single stream) vs MIMO-B (dual stream) on both the uplink and the downlink. Good SNR at the SM is the name of the game on the downlink side.
Like 900MHz, we struggle with the 2.4 band as well, which is why we've decided to stop new deployments in both bands. 3.6 and 5GHz is all that's (mostly) left for us here.
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I find it helpful to look at the discard rates in the throughput stats tab as well. When you're looking at AP saturation, SMs with high discard rates are often the culprits.
So once I figure out the frame utilization How can I use the other tools you mentioned below to help with end user speed?
@CambiumMatt wrote:
You may also want to consider limiting the amount of throughput the customers are able to use by establishing bandwidth profiles using MIR levels in each SM.
Do you have any network monitoring currently? Keep in mind that all PMP 450 equipment has complete MIBs with OIDs for nearly everything, that can be polled via SNMP at regular intervals to help you monitor what's going on.
We also offer Wireless Manager (and soon cnMaestro) to help with this.
James, while you can use the QoS tab to define a MIR on the download and upload on clients with poor SnR, it would probably be more productive to use the Link Status table on the AP to identify clients with poor modulation and then spend some time trying to figure out how to increase the SnR, either by using a higher gain antenna at subscriber side, or possibly moving the client to a different or closer AP. As Matt mentioned you could also split up the sector in half, for instance, if you're trying to cover 90deg, perhaps use two higher gain 45deg or 60deg antennas instead and spread the clients over those two sectors. Another option is using a larger channel width, but that might have the side effect of reducing the SnR to some clients.
Aren't these AP's suppose to have 125Mbps throughput? I know that there is overhead that will reduce this put I am only seeing about 40Mbps of traffic when they are being bogged down. Is there a setting in the AP that I am not seeing that will help with this?
On a 20 MHz channel in ideal conditions. If you're seeing 40 Mbps, that implies to me that you're using a 10 MHz channel or that it's using a lower modulation.
If you enable "Signal to Noise Ratio Calculation during Link Test" when doing a link capacity, it will give you the percentage of each modulation that SM is using. If it's running at 256 QAM, it will show 25% 256, while if it's running at 64 QAM it will show 33% 64. A little unintuitive, but it works.
Keep in mind wireless throughput in a sector is a "shared media"...
First, a quick explanation of the "shared media" aspect of the system. This knowledge base post summarizes the explanation that the SMs that are far away (or poorer signal levels) may be using more of the frame to complete their data transmissions, thereby degrading the overall sector capacity.
Second, there are some other customer experiences that you can read about here. These guys discuss some of the same points you've made here.
So, from my experience, I've done a few tests and found the following results with frame utilization and overall bandwidth use:
- Lowering Burst Caps - from experience, having an AP with burst limits ignored (10 users, all 8x/6x) would drive the frame utilization to saturation with an average bandwidth usage on the AP of about 15Mbps down. We went through this particular AP and set the burst limits to 2Mbps above their QOS package (except when the package exceeded 10Mbps at which point the burst was set to their package, e.g. 10Mbps package gets 10Mbps burst whereas 2Mbps package gets a 4Mbps burst) and the frame utilization dropped by about 40-50%. So check your burst limitations.
- Frame Period - By setting the frame period to 5.0ms as opposed to 2.5ms, the frame utilization of our AP's dropped by about 30-40%. The overall latency increased by about10-12ms but that is a small price to pay for the frame utilization coming down and overall throughput of the AP increasing. Keep in mind that increasing the frame period will approximately double your timing, and other FSK or OFDM radios need to be adjusted accordingly. We HAVE colocated MIMO AP's and FSK's where the MIMO's are on 5.0ms frame period with the FSK at their natural 2.5ms, with a timing mismatch, and have found some interference on the FSK, but generally no adverse effects on the MIMO's. Keep in mind, with colocation, ensure that the FSK's and MIMO's are seperated by about 3m on the tower, and of course pay attention to frequency band's used.
- Bandwidth - We have experimented a bit with setting AP's to 10, 20, and 30MHz bandwidths to see how overall quality of service differs. I have found that by increasing the bandwidth, the overall signal quality goes down (e.g. an 8x/6x on 20MHz may drop to a 8x/4x on 30MHz). To "combat" the signal drops, I found that setting the MIMO to 5.0ms frame period seemed to improve the throughput of those lower modulations. As far as frame utilization and AP throughput, the AP seemed to have increased in both areas, however signal qualities did go down a bit under 30MHz. Like I said, to further improve performance the AP's were set to 5.0ms Frame Period.
and lastly...
- Downtilt - When combatting noise and interference, and improving signal qualities, we found that we had to adjust the downtilt on a few of our AP's. We were experiencing "Wrong Frequency Beacon Detected" on a lot of SM's and found that towers that were further (for example) South of the AP that we were connecting to, were within the same frequency channel range by about 5MHz. Due to our tower coverage, and the frequency's available, we had to adjust the downtilt on the that furthest south AP so that the SM's to the far north did not receive information from the wrong color code on the same frequency range. So something to look at. This did improve service to those SM's that were to the far north. The following link has some handy spreadsheets that will help you determine what your downtilt should be. We aim to have the Outer edge of our AP range about .25mile to .5mile past the furthest SM assigned to the AP.
http://www.acksys.fr/en/support/radio-link-coverage-and-calculation-tools/
It's just important to keep in mind that the lower the modulation rate the higher the frame utlization a customer will use. Two identical QOS packages at 10Mbps/10Mbps will have different frame usage based on their modulation. The 8x/8x may use 5% whereas the 8x/4x may use 20%, so do your best to either limit how m any lower modulations your allow on your AP, or try to improve the modulation rate by installing a dish, improving the LOS, or moving them to an AP which is closer to their location.
I hope some of this information is useful. And if you find other configuration changes that seem to improve your service please share.. =D
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Valuable and practical information Scott! Thanks for sharing.
Better service to the customers is better for business for all of us. So, glad to help. Also, on a side bar, if we can get a final patch for FSK's to allow a 5.0ms frame period, that would be outstanding.