topic Re: Default beacon/dtim settings in Wireless

Default beacon/dtim settings

Trent Hurt — Sun, 04 Jul 2021 07:22:08 GMT

What are folks thoughts regarding increasing the beacon interval as well as the dtim interval on a very large byod data ssid? I know the dtim increases for voice but I'm interested in upping those settings on regular data ssid.

Sent from Cisco Technical Support iPhone App

Default beacon/dtim settings

Amjad Abdullah — Mon, 08 Jul 2013 13:55:09 GMT

That will require bigger buffer on the AP. The AP buffers the data that the clients poll on DTIM period. If the DTIM period (in milliseconds) is too large, the AP buffer might be overwhelmed faster.

If there is no justifiable reason to increase the DTIM rate or the beacon's interfal I don't see any value of incrasing it.

Rating useful replies is more useful than saying "Thank you"

Re: Default beacon/dtim settings

George Stefanick — Mon, 08 Jul 2013 14:11:46 GMT

Understand the value of the DTIM mechanism is to conserve battery life on smaller battery devices. Some vendors, specifically voice vendors spell out very specific DTIM settings. This allows their devices to perform longer. Also note DTIM is for multicast/broadcast delivery. Some applicants get funky when you use extended dtims. Only way to know is to test it .. I don't know I would go more than 3 or so .. But that's just me

As for beacon intervals I wouldn't touch that .. 102 us is default and again some clients get funky if you jack with it ..

Sent from Cisco Technical Support iPad App

Re: Default beacon/dtim settings

George Stefanick — Mon, 08 Jul 2013 14:14:07 GMT

Btw on most devices it states 100, but under the covers 102 is happening.. Sniff some traffic and see .. It's called TBTT

Sent from Cisco Technical Support iPad App

Re: Default beacon/dtim settings

Scott Fella — Mon, 08 Jul 2013 14:24:07 GMT

The best practice guides out there has the DTIM set to 2. Again, each vendor has its own best practices. Spectralink requires the WLAN to have a DTIM of 1. I have used DTIM of 2 with no issues and only a handful require and work well with a DTIM higher than that.

Sent from Cisco Technical Support iPhone App

Re: Default beacon/dtim settings

thefranmanatt — Mon, 08 Jul 2013 21:06:53 GMT

Why do you want to change this? What is the end goal? Any multicast action going on?

CCNP - Wireless
CWNA and CWAP

Re: Default beacon/dtim settings

Trent Hurt — Tue, 09 Jul 2013 00:05:51 GMT

I'm just looking/thinking of ways to free up some airtime. I see lots of management traffic in air when I sniff. I also have true byod environment (.edu) so I'm don't want to break any clients by tweaking beacon intervals or dtim. Was just looking for folks opinions on these settings.

Sent from Cisco Technical Support iPhone App

Re: Default beacon/dtim settings

George Stefanick — Tue, 09 Jul 2013 00:10:43 GMT

I assume you mean 2.4 GHz ? DTIM will not save you any airtime.

Here are a few ideas ..

1. Disable lower data rates - make sure your wifi is design as not to create holes

2. Small cells (lower tx power, hide aps out of sight of each other)

3. Proper channel distance (20 dbm)

__________________________________________________________________________________________
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
__________________________________________________________________________________________
‎"I'm in a serious relationship with my Wi-Fi. You could say we have a connection."

Re: Default beacon/dtim settings

Trent Hurt — Tue, 09 Jul 2013 00:20:05 GMT

Thanks for tips. I have all b data rates disabled. I will look into the tx power settings and start there. This is real issue in hd classrooms etc. I also disable some of the 2.4 radios because of aps running to hot.

Sent from Cisco Technical Support iPhone App

Re: Default beacon/dtim settings

George Stefanick — Tue, 09 Jul 2013 00:25:32 GMT

All b rates as in 1,2,5.5 and 11?

If you are deisgning for HD areas here are a few suggestions.

1. try and get 20 clients per ap

2. Use directional anetnnas to shape the RF.

3. Low power (12.5 / 7 mw) in some cases

4. Disable the low rates

5. Depending on your apps you can test client load balance

6. Band steering as well, but test it

Here is the cisco HD design guide

http://www.cisco.com/web/strategy/docs/education/cisco_wlan_design_guide.pdf

Re: Default beacon/dtim settings

Trent Hurt — Tue, 09 Jul 2013 00:49:16 GMT

Yes those rates, I try to go 25 or less per ap but I will go less. Cisco load balancing doesn't work with the variety of clients I have. Band select is on but some clients are just bad due to drivers. I have found that moving aps away from entrances/doorways where folks come in and out of the room, helps with some sticky client issues. I have also tried diligently to educate professors to encourage folks to disable unneeded wifi devices when they are proctoring exams over wifi. Ever little bit helps but I understand just like folks on airplanes they ain't really turning them all off. Then you pile on airdisplay mirroring or similar tech. And you can pretty much forgot about a decent quality of experience for end users. "But it works fine at my house". Lol sorry ranting

As always thanks for the insight and links George your truly awesome for the wifi folks on here!!!!

Sent from Cisco Technical Support iPhone App

Re: Default beacon/dtim settings

George Stefanick — Tue, 09 Jul 2013 01:25:03 GMT

How many folks do you get in a room that need wifi ?

Sent from Cisco Technical Support iPhone App

Re: Default beacon/dtim settings

thefranmanatt — Tue, 09 Jul 2013 01:36:40 GMT

are you able to sniff traffic?

You may free up some air time disabling those probe suppressing hacks.

Do you have a WCS/NCS/CPI?

What code are you running?

Read over that HD guide George posted. It is a good. Aruba and Aerohive have HD guides worth reviewing also.

FYI, 10-20 seconds after the screen goes black on iphones/ipads they pretty much shut down the wifi. When they are on you would real want them connected so they aren' probing EVERY channel (even the off ones like 2,3,4,5,7,8,9,10), this really slows down their probing. Ever AP that hears the probe replies, If you have 6 aps on channel 1 and they hear the probe they'll all reply. The newer ios version probe at 6mbps.

Kills off the lower rates like 6,9,12, and maybe 18. Add more 5GHz only APs.

CCNP - Wireless
CWNA and CWAP

Re: Default beacon/dtim settings

mmangat — Tue, 09 Jul 2013 02:28:43 GMT

Hello,

The Beacon Interval specifies the duration between beacon packets. Access Points broadcast Beacons or Traffic Indication Messages (TIM) in order to synchronize wireless networks. The default setting of 100 should be ideal for most situations. In a "noisy" environment - one with much interference - decreasing the Beacon Interval may improve network performance. In very remote locations (with few wireless nodes) this value may be increased.

DTIM Interval

This setting determines how often the Access Point's Beacon (TIM) contains a delivery traffic indication message (DTIM). The DTIM tells client devices in power-save mode that a packet is waiting for them. The default setting causes client devices using power-save mode to wake up. To conserve battery power in client devices using power-save mode, increase the Data Beacon Rate (DTIM) setting. However, setting the DTIM too high may cause a wireless client to lose its network connection.

The DTIM is a multiple of the Beacon (TIM). So if the DTIM was set to 3, a DTIM message would be sent with every third Beacon.

Re: Default beacon/dtim settings

George Stefanick — Tue, 09 Jul 2013 02:31:51 GMT

Wonder if these Cisco guys are real or drones with auto reply with subject definitions ..

Sent from Cisco Technical Support iPhone App

Re: Default beacon/dtim settings

Trent Hurt — Tue, 09 Jul 2013 03:09:27 GMT

200-300 users with 3-5 devices in large classrooms

Sent from Cisco Technical Support iPhone App

Re: Default beacon/dtim settings

Trent Hurt — Tue, 09 Jul 2013 03:13:43 GMT

are you able to sniff traffic?
Yes, I said that in earlier post. What are you asking?

You may free up some air time disabling those probe suppressing hacks.

????

Do you have a WCS/NCS/CPI?
PI

What code are you running?
7.4
Sent from Cisco Technical Support iPhone App

Default beacon/dtim settings

Amjad Abdullah — Tue, 09 Jul 2013 06:34:27 GMT

George Stefanick wrote:

Btw on most devices it states 100, but under the covers 102 is happening.. Sniff some traffic and see .. It's called TBTT

102.4 to be more accurate. LoL.

Default beacon/dtim settings

Amjad Abdullah — Tue, 09 Jul 2013 07:53:24 GMT

LoL. They are real

but they copy and paste.

Rating useful replies is more useful than saying "Thank you"

Re: Default beacon/dtim settings

thefranmanatt — Tue, 09 Jul 2013 13:25:51 GMT

If you can sniff the traffic you may want to look at the "QBSS" to see change utilization. Also you can check the beacon to make sure they are getting spit out even 102.4ms. The AP has to content to send it out, so if it the medium is busy you'll see delayed beacons. Though after so many delayed beacons will give itself better chances to access the medium (I forget the details)

Disable load balancing and band select. those are hacks.

In CPI you can run channel utilization reports. This will help you see airtime use

In 7.2 they added a way to limit users per radio. I'd set the 2.4GHz fairly low. This will help move dual band client over to 5GHz. It does run the risk of 2.4GHz users not getting access. In 7.4 you can enable AVC and watch traffic patterns. Give proiaty to the important class stuff and BE the unimportant stuff like facebook etc.

You may want to set up two SSIDs, a fast and a slow. Make the fast SSID 5GHz only. Users that can see it join it instead of getting on the 2.4 radios. Also I'd make the 5GHz 40MHz, this will allow clients that support it use less airtime. Make sure you select your 5GHz channels to match a large % of what you clients support. If only 10% of your clients support unii-2 extended... well don't enable those channels.

CCNP - Wireless
CWNA and CWAP