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Occasional Contributor I

Big Problem with Exam Classroom Wi-Fi Network Instant

Hi All,

 

We have very strange issue and I hope someone will help us out.

We installed 4 demo units of Aruba instant (for test) in one of the Schools for an Exam Room (2xIAP225, 2xIAP215) in one IAP cluster. Topology is following:

AP Connects to HP 1820 (access, 2AP to 2 x1820), then goes to HP 2510 Core and also Cisco 881 is used as a router (and DHCP).

AP's run on latest 6.5.4.3 Firmware.

There are two classrooms, both equipped with approx. 170 Mac PC's. (old ones with only 2.4 GHz support). This Mac's are used for exam purpose and are critical.

Only 2 SSID are used - for exam and for staff.

The problem is following:

When we have like 30-40 users connected everything works fine and performance is good. However, when more devices start to connect and there are approximately more than 100 clients (maxing at 170), we start receiving extremely bad connection (almost no internet access) and applications refuse to work. It's not an internet issue, because when we even try to ping local router (cisco) or even AP the latency is like 8000+ and even connections of Wi-Fi start to drop at all on some clients. When we test router ping on 20-30 users connected only, we receive good 2-3ms ping on router and on switch and AP. 

Internesting is that there is another network used on same network (switches and router) of Ubiquity. When we get problems with Aruba (many users are connected) and test ping with Ubiquity on Router, everything works fine (good ping) and SpeedTest gives good numbers - we also tested same from the Wired network while Aruba's were under heavy load and received good figures. 

So as we see, there is a problem with access points. We tested Ruckus700 and 100 clients worked flawlessly on single AP.  

Can you pleas help figure out what is going wrong? In Instant Admin we see that distribution of clients between AP is usually equal (40x per AP), but i guess 225 and 215's must handle even more users.

 

Any suggestion?

 

Guru Elite

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

 - Under the SSID > Advanced, make sure broadcast filtering is set to "ARP".  Broadcasts are a natural enemy of wireless.

- Under RF>ARM, make sure 80 mhz and Wide Channel Bands is unchecked, because based on your design, you wouldn't have enough channels for it.

 

Start with those changes


*Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.*
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Occasional Contributor I

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

We use drop broadcast to ARP (default) as you noted and 80hz is disabled. No wide channels as well.

Any other suggestion?
Occasional Contributor I

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

Since these clients are 2.4ghz what does your channel utilization for your 2.4 network look like? 

Occasional Contributor I

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

When more and more clients are connecting, channel utilization goes up pretty high. We tried decreasing TX levels, but utilizations still goes up. 

Guru Elite

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

What band are the clients on?

 

You might have to:

- Remove the lower rates on the 

- Enable Broadcast Filtering on All SSIDs

- Turn down the transmit power to the lowest (assuming you are only serving clients in the room that they are in)

- Make sure the 5ghz transmit power is 6 EIRP higher than the 2.4ghz so that 5ghz clients do not end up on the 2.4ghz band.

 

Having higher utilization when alot of clients transmit is unavoidable, but it can be managed, depending.


*Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.*
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Occasional Contributor I

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

Colin,

 

As noted above, clients support only 2.4GHz.

We will try to remove lower rates.

Broadcast filtering is set to ARP.

Transmit power for 2.4 is almost on lowest point (6db)

5GHz makes no sense here because we have no 5GHz clients.

Still utilization goes high and we face the major problem (dropping clients and very high latency not only to internet but to internal network).

I dont know what is a primary cause, is it high utilization or something else.

 

 

Guru Elite

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

You have very few options.  The 2.4ghz band itself does not have much capacity compared to the 5ghz band.  In addition, many devices that are non-wifi compliant operate in the 2.4ghz band and cause interference which increases the utilization and decreases performance from wifi clients because usable bandwidth is much lower than the 5ghz band.  Typical strategy is to move from the 2.4ghz band entirely to open up the spectrum.

 

If you need to stick to the 2.4ghz band you need to evaluate what applications you are using to determine if 30 2.4ghz users can be supported on a single access point, or do we make changes to limit the bandwidth of existing users (bandwidth contracts).  Setting "fair access" does not matter if your usable bandwidth is very small in the first place. 

 

I would first measure the RF utilization at midnight when few to no users are on the network.  If the utilization is more than 10%, you need to ensure that not only the access point in that room is at a low transmit power, but the surrounding access points are also lower.  That will prevent co-channel interference which is caused by your own access points (you typically only have 3 chanels on 2.4ghz band).  You can do that across the board by going into RF> ARM and lowering the maximum transmit power.  Observe the RF utilization on the 2.4ghz band a minute after changing that parameter.  After you do that, I would consider removing the lower transmit rates on those SSIDs and measuring the RF utilization again.  Information on removing lower rates in a controller based system is here:  http://community.arubanetworks.com/t5/Controller-Based-WLANs/Why-do-I-need-to-disable-lower-data-rates-on-802-11g-band/ta-p/174978  The idea is the same in Instant, but the procedure is different.

 

 


*Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.*
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Guru Elite

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

Looking back at your first post, you said you had 2 IAP-225s and HP 1820s. You then need to make sure that the APs that are connected are running at high power, otherwise the 2.4ghz band performance will be hobbled (1x3 instead of 2x2):

 

https://support.arubanetworks.com/Documentation/tabid/77/DMXModule/512/Command/Core_Download/Default.aspx?EntryId=14676

Screenshot 2017-12-25 at 11.25.40.png

SSH into both of your IAP225s and type "show ap tech-support | begin "Power Status" to see if your access points are running at full 802.3at.  Below is the output you want to see:

Power Status

------------

Operational State          POE-AT: No restrictions

-----------------          -----------------------

Current HW State           POE-AT: No restrictions

 


*Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.*
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Occasional Contributor I

Re: Big Problem with Exam Classroom Wi-Fi Network Instant

Colin,

I am not at venue to check it right now but as long as I remember , if AP runs in power reserve, some amber lights must flash. When we observed, there were 4 solid green lights running, meaning no power issues (correct me if I am wrong). Also in setup we have 1x225 and 1x 215 per room. Can it anyway affect performance? I still believe that 40 clients per AP for both 225 and 215 must not be a hard task (cpu usage is quite low on peak connections). Applications are just web based exams, nothing traffic heavy. As observed, problem begins when we start to connect many users, the network just dies. (Even wi-fi connections drop on some).
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