Our environment (residential) is about 80% Mac and I’ve not run into issues with DBS. With a dense deployment, it’s rare that there would be a reason to force a client to another AP as the number of clients per AP is very low i.e. a sticky client isn’t an issue. In less dense deployments it’s likely all radios will be at 80Mhz, making it a non-issue.
If the AP placement is done well from the start, it’s hard to fathom a situation where DBS is going to make a truly bad decision. If it sees an influx of 11g clients, it’s going to reduce width. If the environment is mostly all 11n and 11ac (as it is at my university), it’s going to favor 80Mhz. In general, I favor letting the software make the decisions and only change that if I can demonstrate that it’s causing harm. From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU] On Behalf Of Jake Snyder Sent: Wednesday, November 30, 2016 4:40 PM To: WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU Subject: Re: [WIRELESS-LAN] 5GHz Channel Width One things to keep in mind is that certain device manufacturers preference wider channels. Apple in the Mac OS X products for instance, will always prefer an 80MHz channel over a 40MHz channel. As well as a 40MHz channel over a 20MHz channel. Things like DBS can lead to stickier clients, as you are now mixing channel widths. This leads you to trying things like Opt-R in order to force now sticky clients to other APs, which will likely be less successful since OS X doesn’t support 802.11v. This means DEAUTH, ironically which the OS X devices don’t handle as well as their PC brethren… https://support.apple.com/en-us/HT206207 Selection criteria for band, network, and roam candidates OS X always defaults to the 5GHz band over the 2.4GHz band, as long as the RSSI for a 5GHz network is -68 dBm or better. If multiple 5GHz SSIDs meet this level, OS X chooses a network based on these criteria: 1. 802.11ac is always preferred over 802.11n or 802.11a 2. 802.11n is always preferred over 802.11a 3. 80 MHz channel width is always preferred over 40 MHz or 20 MHz 4. 40 MHz channel width is always preferred over 20 MHz All in all, I would suggest not doing DBS in OS X heavy environments. My preference is to take each building and decide whether it can be leveraged in 20, 40 or 80, and configure the whole building that way. For how to decide if you can get away with 20 vs 40 vs 80, my preference is to pick the channels you want to use, and start with a survey. Let’s say you want to enable UNII 1 and UNII 3. That’s 8x 20MHz Channels. Could i go to 40MHz? If i can get away with 4 channels, then yes. Or I could add channels until i get to the number of channels needed to maintain channels separation. This varies wildly based on density of APs in a building. Eventually you run out of channels that you can add and then must either deal with co-channel interference or drop down to a narrower width. Start with 20MHz How many channels do i need with my current design to maintain channel separation? (Survey may be necessary) Do i have twice that many channels enabled at the current channel width? If yes, increase channel width to 2x current channel width. If no, do i feel comfortable adding channels to get to twice that? If yes, add channels and increase channel width to 2x current channel width. Hope this helps Thanks Jake Snyder On Nov 30, 2016, at 12:03 PM, Jeffrey D. Sessler <j...@scrippscollege.edu<mailto:j...@scrippscollege.edu>> wrote: Depending on the building construction, and assuming you are using DFS channels, running 40Mhz and even 80Mhz is very likely with no downside. 5GHz does not propagate very well, so a static 20Mhz plan in anything but big open spaces is IMHO unnecessary. If you are a Cisco customer, enabling DFS (Dynamic Bandwidth Selection) is likely the best choice for maximizing the use of the 5Ghz space. DFS will dynamically adjust width based on the client make up and other factors, and I’ve found it to be far better than a human design since the environment is never static. I have a newly completed 110-bed residential hall with a very dense deployment of APs (105 AP’s total), most are in-room/suite. With DFS enabled, a clear majority of the in-room APs run at 80MHz. In more public and/or open spaces, they tend to adjust to 20Mhz or 40Mhz. Most of the clients in this residence hall are 11.ac and report a 1300 or 1170 Mbps connection speed. Jeff From: "wireless-lan@listserv.educause.edu<mailto:wireless-lan@listserv.educause.edu>" <WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU<mailto:WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU>> on behalf of "Trinklein, Jason R" <trinkle...@cofc.edu<mailto:trinkle...@cofc.edu>> Reply-To: "wireless-lan@listserv.educause.edu<mailto:wireless-lan@listserv.educause.edu>" <WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU<mailto:WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU>> Date: Tuesday, November 29, 2016 at 1:35 PM To: "wireless-lan@listserv.educause.edu<mailto:wireless-lan@listserv.educause.edu>" <WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU<mailto:WIRELESS-LAN@LISTSERV.EDUCAUSE.EDU>> Subject: [WIRELESS-LAN] 5GHz Channel Width Hi All, I was just reading a blog article that heavily recommends not to use 40Mhz channel width in multi-floor environments, particularly where many 5GHz radios are used (particularly in our case with Xirrus multi-radio APs). Our campus presently uses 20MHz channel width in all buildings. We are testing and considering 40MHz width because of the bandwidth benefits for clients. What do you use on your campus? Have you found that setting a 40MHz channel width on your 5GHz radios has caused too much interference? Here is the article: http://divdyn.com/dual-5ghz-radio-aps/ Your thoughts are appreciated. -- Jason Trinklein Wireless Engineering Manager College of Charleston 81 St. Philip Street | Office 311D | Charleston, SC 29403 trinkle...@cofc.edu<mailto:trinkle...@cofc.edu> | (843) 300–8009 ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found athttp://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
