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rtacheny
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AP Bandwidth and Latency Issues

Thu Sep 19, 2013 1:56 am

Hello all!

I work for an ISP in the states, and one of our towers has been giving us massive issues. It would appear that our access point is only allowing between 2-4M of simultaneous bandwidth among the connected clients. We have been struggling with this equipment for quite some time now, and have replaced everything equipment related at least once. I have tried multiple iterations of RBos including 6.2/5.26/5.25/5.24 to no avail. This is what we use, assume anything not listed at default or disabled.

Omni 2.4 Access Point

RB711UA-2HnD
arp=enabled
Atheros 11N
ap-bridge
2457 @ 0 Usage -118 Noise Floor
2ghz-onlyg
10mhz
802.11
B/G/N
default-authentication=yes
no_country_set
superchannel
7 Hw. Retries
Hw. Fragmentation Threshold: 1024
adaptive noise immunity: ap and client mode
CURRENTLY 25 CONNECTED CLIENTS

Our CPs Vary. We have some Engenius 2610 and 2611s, UBNT Bullet and PS, RB112, RB411, RB711, and SXT, perhaps a few other misc tiks.
All clients are Queued at the radio for Upload, on a Tik cloud here in the office for download. Tx signals vary between -50 to -80
Our used bandwidths are as follows: 1M down / 512K up ; 2M down / 1M up ; 3M down / 1.5M up and 5M down / 2.5 up.
rts/cts enabled
adaptive noise immunity: client
Hw. Retries: 7

Any ideas would be greatly appreciated. I would be happy to share any info that may help make things more clear.
 
SamWCL
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Re: AP Bandwidth and Latency Issues

Sun Sep 29, 2013 10:49 am

What is your furthest client from the AP?

It could be a mixture of things. Such as tx/rx rates, and some thing on auto etc.

Could also be due to multiple vendors connecting to the same AP.
 
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rtacheny
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Re: AP Bandwidth and Latency Issues

Sun Sep 29, 2013 5:15 pm

What is your furthest client from the AP?

It could be a mixture of things. Such as tx/rx rates, and some thing on auto etc.

Could also be due to multiple vendors connecting to the same AP.
Thanks for the reply!

I suspect multiple vendors to be the main cause myself, but am trying to explore a more cost effective solution if possible. We want to get everyone on tiks eventually, that is our goal, but we have many access points, and 1000 customers, it keeps our techs pretty busy, and our wallets pretty slim to make large network changes. Since posting this, we have decided to put up 3 120 degree sectors to replace the single radio/omni access point. However, I know we have a couple other APs that are in a similar situation that are already sectored that we have received some complaints from.

To give you an idea as to what we have for TX/RX, here is what it looks like:

-77
-49
-63
-49
-73
-56/-72
-66/-70
-70/-73
-37/-49
-60/-66
-38/-60
-57/-61
-77/-78
-76/-81
-55/-62
-57/-72
-43/-47
-39/-66
-53/-58
-53/-57
-79/-79
-61/-67
-43/-64
-70/-69
-48/-51

Thoughts?
 
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Re: AP Bandwidth and Latency Issues

Sun Sep 29, 2013 6:04 pm

Personally I try to hit around -60 for all signal levels (my rule-of-thumb limits are -55 to -69). Those you have that are in the -30's and -40's are way too hot - you need to dampen them down a bit. Those that are in the -70's and -80's might be too weak and are spoiling the party for everyone. Try to get everything in to the same ball-park, and those that you cannot, put them on a different AP.

Secondly, I guess you're running plain 802.11 (no TDMA protocol). If you've got users scattered all over the geographic area, you'll most likely need a TDMA protocol, at the very least to help with hidden node issues. Your plan at sectorising will help. Don't forget if you're putting 3 sectors where you had 1 omni, you'll probably need some shielding to prevent self interference (depends on your setup really).

I think your long term goal of standardising on one vendor (eg: MT / SXT) and using something like NV2 will give you the best result.

Rich
 
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rtacheny
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Re: AP Bandwidth and Latency Issues

Tue Oct 01, 2013 5:18 pm

Personally I try to hit around -60 for all signal levels (my rule-of-thumb limits are -55 to -69). Those you have that are in the -30's and -40's are way too hot - you need to dampen them down a bit. Those that are in the -70's and -80's might be too weak and are spoiling the party for everyone. Try to get everything in to the same ball-park, and those that you cannot, put them on a different AP.

Secondly, I guess you're running plain 802.11 (no TDMA protocol). If you've got users scattered all over the geographic area, you'll most likely need a TDMA protocol, at the very least to help with hidden node issues.
I do tweak the Tx Power to get them at least above fifty, I could try and tweak the numbers more to what you say. However, the -30's and -40's you speak of are Rx signals, so unless I can get them with a smaller radio/antenna (which I can't), how do I deal with that? Also, you said the -70's and -80's actually effect everyone? Out of curiousity, how so?

I do have rts/cts enabled for hidden node issues.
 
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Re: AP Bandwidth and Latency Issues

Tue Oct 01, 2013 5:34 pm

It can very difficult to trace what item(s) is causing the issues when you use that variation of CPE's, I would have Mikrotik only CPE's and use NV2 which eliminates hidden nodes, Latency on NV2 - no complaints from customers using this protocol.
 
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rtacheny
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Re: AP Bandwidth and Latency Issues

Tue Oct 01, 2013 7:37 pm

It can very difficult to trace what item(s) is causing the issues when you use that variation of CPE's, I would have Mikrotik only CPE's and use NV2 which eliminates hidden nodes, Latency on NV2 - no complaints from customers using this protocol.
This is our ultimate goal. Unfortunately the company has gone through a lot of different manufacturers and models over the years, trying to find what works best, and to fill gaps that have only more recently been filled by Mikrotik. We are now set on using all Mikrotik equipment, but it is quite a large investment of resources to go out and replace all clients radios. We have almost around 1000 customers, I would bet somewhere around 100 of them are still on Engenius, and 200 on UBNT.
 
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Re: AP Bandwidth and Latency Issues

Tue Oct 01, 2013 10:30 pm

It can very difficult to trace what item(s) is causing the issues when you use that variation of CPE's, I would have Mikrotik only CPE's and use NV2 which eliminates hidden nodes, Latency on NV2 - no complaints from customers using this protocol.
This is our ultimate goal. Unfortunately the company has gone through a lot of different manufacturers and models over the years, trying to find what works best, and to fill gaps that have only more recently been filled by Mikrotik. We are now set on using all Mikrotik equipment, but it is quite a large investment of resources to go out and replace all clients radios. We have almost around 1000 customers, I would bet somewhere around 100 of them are still on Engenius, and 200 on UBNT.
For me, migrate to mikrotik is not a good idea, you will have problems that you never imagined.
 
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rtacheny
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Re: AP Bandwidth and Latency Issues

Tue Oct 01, 2013 10:59 pm

It can very difficult to trace what item(s) is causing the issues when you use that variation of CPE's, I would have Mikrotik only CPE's and use NV2 which eliminates hidden nodes, Latency on NV2 - no complaints from customers using this protocol.
This is our ultimate goal. Unfortunately the company has gone through a lot of different manufacturers and models over the years, trying to find what works best, and to fill gaps that have only more recently been filled by Mikrotik. We are now set on using all Mikrotik equipment, but it is quite a large investment of resources to go out and replace all clients radios. We have almost around 1000 customers, I would bet somewhere around 100 of them are still on Engenius, and 200 on UBNT.
For me, migrate to mikrotik is not a good idea, you will have problems that you never imagined.
Could you please elaborate a bit on this? We have had great luck with Mikrotik, and are quite set on using nothing else because of what it allows us to offer in terms of troubleshooting, and options for possible fixes to issues we are having. Mikrotik also allows us a great selection of products to fill the roles that we need as a wireless ISP.
 
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Re: AP Bandwidth and Latency Issues

Tue Oct 01, 2013 11:25 pm

....................................................

For me, migrate to mikrotik is not a good idea, you will have problems that you never imagined.
I have 100% Mikrotik network and very pleased to say after we addressed issues as they occurred, it’s now a very stable network.
But as I think back to get to that level of stability you need to have a lot of expertise and experience in several areas like RF, networking, programming, etc., if you don't have that in-house, get people who have, to configure and work through any issues.
 
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Re: AP Bandwidth and Latency Issues

Wed Oct 02, 2013 9:16 am

I do tweak the Tx Power to get them at least above fifty, I could try and tweak the numbers more to what you say. However, the -30's and -40's you speak of are Rx signals, so unless I can get them with a smaller radio/antenna (which I can't), how do I deal with that? Also, you said the -70's and -80's actually effect everyone? Out of curiousity, how so?

I do have rts/cts enabled for hidden node issues.
Just to clarify - these RX levels are seen at your AP, right? For the -30's, reduce their TX power or change their antenna.

For the weak clients, most likely a low signal level will translate to either low data rate, low quality, or both. So if you have just 1 client that is at a slow air-data rate (say 6mbps) and everyone else at something higher (say 130mps), then that slow client will take 21 x longer to transmit data. Therefore whenever that slow client is communicating on the network it is taking up 21 times as much airtime to transmit a frame of data, preventing others from using the air, and therefore slowing everything down.

Re RTS/CTS, this is not the best solution. In itself, it will slow things down because there is a lot more "negotiation" for each frame being sent. Secondly, collisions will still occur (there's no coordination for transmission of RTS packets in the first place). Best option would be to implement NV2 (or similar), but that would require standardising your AP/CPE vendor which you've already discussed.

Given you need to get the biggest effect from a low budget, spend some time to stabalise signal levels, and TX/RX data rates. Try moving slow clients to a separate AP if you cannot tune them inline with everyone else. Secondly, sectorisation will reduce the effects of hidden nodes, poor signal clients, interference, etc (but make sure the sectors are adequately isolated from each other).

Rich
 
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rtacheny
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Re: AP Bandwidth and Latency Issues

Wed Oct 02, 2013 7:46 pm

I do tweak the Tx Power to get them at least above fifty, I could try and tweak the numbers more to what you say. However, the -30's and -40's you speak of are Rx signals, so unless I can get them with a smaller radio/antenna (which I can't), how do I deal with that? Also, you said the -70's and -80's actually effect everyone? Out of curiousity, how so?

I do have rts/cts enabled for hidden node issues.
Just to clarify - these RX levels are seen at your AP, right? For the -30's, reduce their TX power or change their antenna.

For the weak clients, most likely a low signal level will translate to either low data rate, low quality, or both. So if you have just 1 client that is at a slow air-data rate (say 6mbps) and everyone else at something higher (say 130mps), then that slow client will take 21 x longer to transmit data. Therefore whenever that slow client is communicating on the network it is taking up 21 times as much airtime to transmit a frame of data, preventing others from using the air, and therefore slowing everything down.

Re RTS/CTS, this is not the best solution. In itself, it will slow things down because there is a lot more "negotiation" for each frame being sent. Secondly, collisions will still occur (there's no coordination for transmission of RTS packets in the first place). Best option would be to implement NV2 (or similar), but that would require standardising your AP/CPE vendor which you've already discussed.

Given you need to get the biggest effect from a low budget, spend some time to stabalise signal levels, and TX/RX data rates. Try moving slow clients to a separate AP if you cannot tune them inline with everyone else. Secondly, sectorisation will reduce the effects of hidden nodes, poor signal clients, interference, etc (but make sure the sectors are adequately isolated from each other).

Rich
Interesting input ion the RTS/CTS. Because not everything is possible for me to do, would you say it is a safe bet to disable RTS/CTS on radios with better signal strengths, such as below 70, and leave it enabled for less reliable connections 70 and above so that they don't spoil the connection for the rest, or create a hidden node?
 
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Re: AP Bandwidth and Latency Issues

Thu Oct 03, 2013 10:31 am

Hi rtacheny,

RTS/CTS is not a mechanism to improve performance of weaker clients, it's a mechanism to coordinate transmission of data and attempt to avoid issues like hidden node. So I don't believe disabling on stronger clients will benefit the system as a whole. I'm not very experienced with the practical use of RTS/CTS as I've never used it in the WISP environment (only TDMA like NV2), so I can't offer authoritative advice. However, if I were in your position I would not disable RTS/CTS selectively (based on theory rather than practice), but YMMV.

If I were you I would run an "experiment"! I would setup a second AP at one of your troublesome sites and move your Mikrotik clients to it running NV2. You may want to do similar with any UBNT you have with Airmax. Demonstrate to the business owners that migrating to a single vendor and running a TDMA protocol will have real benefits (including customer satisfaction & retention in the long run) and convince them to invest in rolling upgrades. Even with this approach, you still need to balance signal levels.

As a second (or additional) approach, setup a second AP and divide clients above -70 and below -70 to the two AP's. At least this way, you limit the "damage" the poor performers will cause. I still think you need to do something with those > -50 clients also, but they may be less critical than the weak ones. Have you turned down the TX power on those very strong clients?

Unfortunately none of this is exact science! There are possible issues evident from the info you posted, but there may also be some other factor that is causing your slow speeds (eg: interference, damaged cables, etc). Tune what you have as much as you can to the parameters we've discussed (eg: signal levels) as this will not cost you anything. Then run some trials with the infrastructure upgrades (sectorisation, TDMA, client division based on signal, etc) and see what works best, as this is where the investment is required.

Rich
 
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rtacheny
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Re: AP Bandwidth and Latency Issues

Sat Oct 05, 2013 2:50 am

All of this has been helpful so that I can mull over different things in my mind. Today we finally got to sector that access point, and I'm already seeing the bandwidth graphs double. However, the more I play around with rts/cts values at 802.11 sites, the more I don't like it. It seems that enabling RTS/CTS negatively effects constant bandwidth. Instead of a customer having a nice clean, constant flow of bandwidth, they hop up and down, and overall, it would seem it has a negative impact on overall bandwidth. We have used nstreme on quite a few sites, but I am really focusing on NV2 as it seems to make a massive difference in connection reliability. One more thing that is kind of boggling my mind is people, and the Mikrotik wiki, talk about features using more system resources. I have been playing around with hw fragmentation threshold and am not sure the best way to set it up. I currently am only putting it on the client side, and not the AP, and it seems to help, but this could be just placebo. I have been setting it at 256, and have yet to see any noticeable impact on CPU/RAM usage on either the AP, or client side. Am I setting up hw fragmentation wrong? Or does Mikrotik exaggerate on how "demanding" it is? Also, on Hw. Fragmentation, should it be used in conjunction with 802.11, nstreme, and NV2? Or is it better off only being used with certain protocols?
 
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Re: AP Bandwidth and Latency Issues

Sat Oct 05, 2013 2:39 pm

........................Also, on Hw. Fragmentation, should it be used in conjunction with 802.11, nstreme, and NV2? Or is it better off only being used with certain protocols?.........................
I use NV2 and got conflicting advice on the forum from other users about the use of certain wireless setting when using NV2 - So i asked Mikrotik to simply grey out or remove setting not used when certain wireless protocols were selected as there is nothing worse than wasting a lot of time changing setting even rebooting to check, when they have no effect on the selected protocol.
 
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Re: AP Bandwidth and Latency Issues

Sat Mar 08, 2014 5:21 pm

It's been awhile since I have posted in this thread but I figured I would post my results here. Note that the average noise floor is around -100dBm or lower where I am at. I have used these settings on radios with versions 6.5 - 6.10 What I found to do the trick (and most effectively) is as follows:

Mixed Client access points (stuck with 802.11):
Disable RTS/CTS (leave on for exceptionaly low signals -76dBm or lower, ideally, don't install in this range) It kills throughput, and causes problems.
Enable ANI on ALL clients, and set AP to AP and Client mode.
Enable HW. Fragmenation, 256. DO NOT ENABLE with Engenius 2610 & 2611. There is some kind of bug on the upload and you can lose radios.
Adjust TX signals so that signals are lower then -60dBm. Stronger signals kill the throughput.
Try to space AP frequencies by at least 20mHz on 2.4Ghz. You will hit noise issues whenever you have anything closer than that in the surrounding areas.

All MikroTik Client access points:
Set to NV2
Adjust distance to ~ 20% higher than the highest distance radio in tower. You may need to play around with this number if you are having issues.
Adjust TX signals so that signals are lower then -60dBm. Stronger signals kill the throughput.
Remove radios with signals -74dBm or lower, unless you can improve signals. NV2 is more picky when you have weaker signal clients in tower, and it will kill the overall AP throughput.
Make sure to test frequency ranges outside of the norm, I find 2477-2487 to be exceptionally clean in my area, although this may differ for you.

Avoid using nstreme, you can run into some goofy problems. Sometimes it works nice, but It doesn't seem to be consistent. If NV2 is not working well, you are doing something wrong.

For Both of these types of APs.
Try to use newer radios on your APs, such as 711, 912, ect. Spectral-History is a very valuable feature, and you will find that it will be FAR more useful and important then what you see when running a Freq Usage test.

I hope someone may find this post helpful in the future!

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