Access point lock up due to simultaneous users??

[BobY777]

I'm concerned about access point lockup due to many simultaneous users.

We all know that many simultaneous users may slow down an access point. Thats normal and reasonable.

Access point manufacturers will recommend a certain maximum number of users due to the slow speed that naturally happens.

BUT what they don't tell you is THEIR ACCESS POINTS CAN LOCK UP if too many simultaneous users get on an access point. I have heard that this isn't manufacturer specific?

I hope someone gets on here and tells me I'm all wet.

If not, this sounds like a big problem. How is a WiFi installer to know when too many simultaneous users have been on an access point in a WiFi installation that they installed 500 miles away from their office. The venue operator won't know.

I haven't seen this issue spoken of before. But it doesn't sound too good.

Is it possible that only a few simultaneous users can lock up an access point if they are downloading lots of data, as with music or video, etc? Or is the only factor in AP lockup, the number of simultaneous users?

Seems one way around this, is some APs will allow a limit on the number of WiFi users that can associate to that AP, so that there aren't too many simultaneous users.

Lets say this is in a hotel with 6 APs. What if we put a limit at 15 users on all the APs. Lets say we have 15 users on one AP (this can be done on some APs like the Senao AP Pro Plus). What happens to the 16th person who wants to associate to that AP? How will his PC card know to associate to the next strongest AP, which may be available and able to carry traffic. I don't think his PC card will know to go to the next strongest AP, even if the next strongest AP is able to carry the traffic.

I have a feeling the 16th person will just be associated to that AP and not able to carry traffic, until one of the 15 logs off.

The only other way is to assume that all the APs are locked up, even if they aren't. That is, put a digital timer on all the APs and once a day power cycle them once. Assume they need to be power cycled, even if they don't need the power cycle, due to lock up. Thats one way to get them out of lock up automatically.

I still don't know how to get the 16th WiFi user to go to the next strongest AP. Any ideas?

I would love to hear from any of you who have addressed this issue.

[spiderbite]

Hi Bob,

Sounds like you may have learned the hard way that " coverage is not throughput" .

I don't know about physically locking up, but many things can be your problem.

1. Same Channels overlapping each other will cause much contention. You only have so much pipe to stuff all that data in.

2. Throughput requirements? just how much throughput will each user need and how many of these users will be in one spot? The answers to these questions combined with your physical survey and any specific client requirements will tell you how many you need.

What are the power settings of your AP's if I may ask? Maybe I can help you out.

Lower power - smaller cells - more aggregate throughput - better load balancing

and less likely to overlap same channel cells.

If you can turn the power down low enough to not associate between floors this (in my opinion) would be ideal.

There are many ways to do things but I'm happy with this one.

Nothin but love Bob, Let me know if I can help.

Anybody that jumps in this biz like you did is ok in my book. You got stones man...God bless ya!

[BobY777]

Hello spiderbite:

Thank you for your reply. I really appreciate it.

I always knew about wanting to keep the cells small and not have overlapping channels. Small cells so that there aren't too many people on one AP. And non overlapping so that there is no interference from one AP to another AP.

But I'm hearing from the manufacturers themselves, that most all APs from all mfgs, can lock up if too many simultaneous users get on them. They don't seem to be able to tell me exactly why this happens though. One place said they thought a buffer gets full with too much data.

I wonder if WiFi installers on here have run into locked up APs in their WiFi installations. That can be a problem if they have to go several hundred miles just to reset the APs. And the only way they will know they aren't working is if they get complaints, since alarm reporting isn't built into the WiFi system.

Now I don't know that I ever had more then 10 people at once on any one AP in the hotel. I'm wondering if a few users can lock an AP if they all try to download music, etc...anything that is heavy in data.

I'm using directional antennas to help keep one channel from overlapping the same channel elsewhere in the building. I think I'm ok there. I'm putting the directional antennas on the top floor and shooting them down to the bottom floor. Seems to work great for a couple h otels I have. Although this doesn't work in all hotels depending on the th ickness of the floors.

The APs are 23 dBm, which is great for getting through the thick hotel floors and walls. But I'm pretty sure that I don't have any overlapping channels.

And I'm pretty sure I haven't had all that many people on each access p oint. We have 6 APs in this one hotel. Sometimes I wonder if some of the people may have viruses in their laptops that can cause the APs to lock up.

I'm thinking I might just put a digital timer on the APs and turn them off for a minute and back on every day. Maybe 3 AM. I'll just assume they are locked up and power reset them. I don't think it can hurt anything.

I did find out that I have had a defective switch. I'm wondering if the switch may have caused some of our APs to lock up.

[BobY777]

I thought I'd post what I found out since yesterday.

I have done some calling around to resellers and manufacturers and I don't think there is any way at all to have a wireless client's laptop move over to the next strongest AP (that might be in the same room), other then having that wireless client actually move closer to the 2nd access point, so that it now is the strongest AP.

A problem will probably occur where the wireless client will be stuck on the prior AP, since it also has a good signal (even if it is the 2nd strongest now).

Seems like the two APs will need two different SSIDs and the wireless user will need to know those SSIDs and how to change to them within their wireless client software, in order to get on the 2nd strongest AP.

I guess this stuff just isn't all that automatic.

People tell me that you can have roaming with the APs, but the wireless user still has to move to the 2nd strongest AP (to make it the strongest signal), in order to roam to it.

I want to be able to automatically move to the 2nd strongest signal without having to move.

[BobY777]

Regarding the lockup problem, I still don't quite know what makes an AP lock up. The manufacturers didn't either. I would think someone there would know, but they don't put the real engineers on the phone.

One person told me they think a buffer in the APs gets overloaded with data, possibly due to retransmissions due to a poor signal or one or a bunch of people are trying to download heavy data related files.

I also have heard that there are viruses on WiFi users laptops that can cause heavy data transmission, and the WiFi user doesn't even know it.

I think the best way around this is to use a digital timer to power recycle the AP each day. That is, just assume it is locked up (even if it isn't) and power recycle it. WiFi systems don't have alarm reporting built in, so we just have to assume the APs are locked up. Automatic power recycling is so easy to do.

Same thing could be done for any other pieces of equipment in a WiFi system that is prone to lockup.

I wonder if lowering the speed that the APs can operate at (which will force WiFi clients to operate at slower speeds), will help in AP lockup? Maybe force them to operate at 5 Meg (or next slower speed) between the APs and WiFi client. This sure would slow down the data transmission to the AP. This shouldn't be a big deal since the speed bottle neck will probably be the ISP speed.

I would love to hear from others here on why they think APs can be locked up.

[spiderbite]

Bob,

You would have to have ungodly amounts of traffic to make an AP slow down to the point of not being usable.

An AP (5.5Mbps) is up there with like two T-1's and some change!


If a buffer is getting full and locking up that means something on the hardwired side isn't letting the buffer dump.

Is the wireless on its own VLAN / Subnet etc...?

If you are all on the same subnet you are subjecting the AP's to ALL the network broadcasts and traffic that have nothing to do with it...


More info on the setup please...

[spiderbite]

Hotel customers usually dont need a roaming capability.

However, There are usually quite a few of them and I believe you may want to rethink that survey (HINT!)


When I said small cells I meant really small cells - You probably shouldn't be able to pick up AP's on different floors.

If you are going between floors, you are probably overlapping same channel cells and people on whatever floor are probably able to associate to whatever AP.

You no longer have any load balancing capabilities.

Please try this>>>

Re- do your survey - make the cells small enough so you cant see them between floors. (lower the power)

This will give you the throughput you need to cover the number of users.

You could have 200 people in a hotel...only six AP's???


That aint enough....

[BobY777]

Hello Spiderbite:

Thanks again for your help.

The hotel that has had some problems, has 6 APs. Only about 100 rooms and 3 floors.

I don't think I have channel overlap. I have the directional antennas on the top floor and shooting down from the 3rd to 1st floor. It's like a big long hallway...6 APs. It starts on one end as: Channels 1, 6, 11, 1,6, 11.

There aren't any APs below the 3rd floor and all directional antennas are pointing down. The distance between like channels is about 80 feet or 90 feet. And the directional antennas help to keep the signals away from the other AP areas.

The hotel only has about 100 people at the most.

I did discover a bad switch, which I changed out. I'm wondering if the switch was causing the APs to lock up.

All 6 APs have the same SSID and on the same subnet.

I don't know that my Internet gateway has the capability of having more then one subnet on the local side.

I would almost have to add a managed switch to get an extra subnet.

There really is no other traffic then just the 6 APs.

I hope I gave enough information.

[BobY777]

Hi Spiderbite:

I appreciate all your input. You must have a lot of WiFi experience.

I did have a question on something you said. I'll put it between the < > symbols:

<If you are all on the same subnet you are subjecting the AP's to ALL the network broadcasts and traffic that have nothing to do with it...>

I thought that if a hotel has, lets say 12 APs that all of them go to the same switch and then on to the Internet gateway. And all the APs are on the same subnet.

I thought since I'm sending all 12 APs into a switch, doesn't the switch direct the traffic to the Internet gateway and not send any data to the other APs?

If I used a hub, I would think a hub would send traffic to everything that is plugged into the hub ports. But I thought a switch would not be sending data packets to all the other APs, since that data is meant for the Internet gateway.

So I never gave consideration that other APs data, could cause lock up for other APs on the same subnet, when going into a switch.

Thanks much for your thoughts (and also for anyone elses thoughts on this too).

[badger11]

Read this tutorial for a better understanding of how switches operate.

http://computer.howstuffworks.com/lan-switch7.htm

If you want to create vlans you will need to ensure that your switch and router or ewg suppport vlans. Not sure if the d-link dsa 3100 gateway supports vlans or not. ( i have seen some of your posts before and am not sure if you are using the 3100 on this site or not)

[spiderbite]

Thanks Bob. I've only been at this for six years. But it is the only thing I have done for six years. Actually, I recently learned how to network a printer!

Thanks Badger for the switch link. I can understand that!

I see where you are going with the design and hey if it works, I'm all for it. I certainly am not the alpha and omega of wireless networking, ( but I know where he lives!):D

What I meant about the Vlans being separate...The hotel has traffic that come from the mothership (email, reports, etc..) that have nothing to do with wireless access. This traffic should never be on your wireless segment.

Probably only broadcasts, but the idea is to segregate the unnecessary braodcast traffic (which is no big deal at 100Mbps) away from your precious 5.5Mbps wireless segment!

Good eye on the bad switch. I bet you'l be fine in no time...

[spiderbite]

BTW,

I have been re reading some of your info - 23dBm is a 200mW radio.

That's booming! (nothing wrong with it, just different)

Even if the cells are far enough apart so as not to overlap think about this...

100 users / 6 AP's = thats almost 20 people per AP if it the network is fully utilized.


The AP probably could handle this but this is a little too thin for me. I need more fail safe to sleep at night.

Plus you figure not everybody is on at once all day long... just between - 7pm and midnight.


I like the directional antenna thing.

what is the signal like outside in the parking lot? You do not need to catch the clap from someone getting free bandwidth from outside.

[BobY777]

Thank you badger11 and spiderbite:

This forum stuff is so neat. We all can take what we know and contribute to each other. And sometimes I may think I may know something and I get it calarfied by others. So I appreciate all your input.

Thanks badger 11 for the switch link.

Spiderbite, since I have learned about the ram in the APs, I'm now wondering why manufacturers don't address that in their advertisments.

The manufacturers talk about many AP features, but I don't see manufacturers talking about how many simultaneous users can be on their APs, and how much memory is in their APs. And I would imagine there is a microprocessor in their AP...they don't talk about the speed of that microprocessor.

That a manufacturer does not mention all this makes me wonder why. I wonder if they are trying to hide something.

Spiderbite, 6 years is quite a while. I'm sure you have tons of experience.

Oh...the signal is fairly weak outside the hotel. Although if someone had a high gain antenna, they might be able to pick up the signal, but they still would need the User ID and password for the week.

Just curious...I think I remember seeing where you said you do WiFi for a living? May I ask what APs you use? Internet gateway?

We use the Senao AP Pro Plus. It has great power out and very good sensitivity. Has PoE.

We use the DLink DSA 3100 for the Internet gateway. Great features for the price. Only problem is that they have had an infrequent lock up problem. Their v2.23 firmware was supposed to fix that, which has been out for a while. I'm thinking that the switch problem I discovered, may have caused the DSA 3100 to act up at times.

Badger11...are you in the WiFi industry also?

Have a nice weekend.

[badger11]

No, but I have an interview with a wireless network integration comapny tomorrow. I have 8 years of IT experience, 4 of which deals primarily with cisco equipment.

Wireless device manufactures are not created equal. You get what you pay for. Here is what I gather from reading and talking with wireless integrators. Cisco and proxim are good access points for commercial use. Motorola canopy equipmnet is good fo point to point and multipoint networking.

The more ram you have the more sessions you can have on the access point. Cpu speed is alos very important. If a company does not list those specifications then it is most likely a cheaper quality and you might want to avoid using that particular model.
Just my .2 cents worth.

Have you figured out the d-link dsa 3100 lock up problem. I am interested in this device as well as nomadix.

[spiderbite]

Bob,

Everything is Cisco...routers, switches etc....


Badger - Did you call Jim?

[BobY777]

Hi all:

Good luck Badger with your interview. You should do well with your experience.

At one time I considered Proxim, until I found out that they have looow power output. Around 15 to 17 dBm. It just can't get through hotel floors and walls. Although they have good management features.

DLink may have the lock up problem fixed. their v 2.23 firmware is supposed to have it fixed. They did come out with v2.27 beta firmware. We will test that soon.

But the DSA 3100 is very good price quality ratio. About $1900 less expensive then the Nomadix. But if money is no issue then Nomadix is good. Although DSA 3100 does have a firewalled section for a private side also.

I think a defective switch made the DSA 3100 look bad at times. I replaced it. So far the DSA 3100 is working fine.

I did run into someone lastnight who had a rogue access point in a hotel room where we have WiFi. I tracked it down to the exact room using a directional ant. with a high front to back ratio. When I found it, the signal mysteriously was turned off. It was on for an hour or more before that.

I wonder if he was on there trying to get prople to associate to it, to get their credit cards. I didn't have time to associate to it, after I located it down to the room. I'm going to keep my eye on that hotel in the future for rogue access points. I first noticed it because it was making my the switch data light, which goes to a particular AP (on the same channel as the rogue AP), flicker like mad. I wonder if this could also lock up APs. It might.

[badger11]

Hey Spiderbite, Thanks Boby777,

I sent Jim an e-mail with no response yet. He may have someone already in the area or might not have any work in my area.

I agree with you about Cisco, I have heard that they have %50 of the commercial installs of ap's. I have heard that people have had problems with Cisco bridges and that motorola canopy is the way to go on bridges. Any thoughts on that?

The dsa 3100 looks pretty good with what you get for the price. Do you know if you can use vlans with the dsa 3100?

[FlaWireless]

We use about 85-90 % Cisco on our installs, the others would be Proxim. The Cisco bridges 1300 and 1400's work great in both PTP and PTMP. We have had some problems with the Proxim PTMP's