Posted on November 20, 2019 6:39 pm
 |  Asked by Trinity Trammell
 |  57 views
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Arista really doesn’t like 4000+ character questions, and I do not blame them.

I don’t know exactly how odd of a question it is for this forum, but I figured it would be better to drop it over here rather than on the Arista WiFi Community forum.

I understand enough about wireless to feel comfortable, but not enough to truly understand why something is the way that it is;
initial testing of the product went well, but actual production usage is back-and-forth. Solely regarding the Intel Wireless WiDi protocol for screen casting (or Miracasting),
would having multiple wireless devices around the targeted equipment cause consistent issues with connection?

TL;DR, with full explanation in the file attached:

We have a building, and a area that is an L-shape:
5 rooms, 30 student laptops per room, 7 employee devices per room, 1 C-130 AP per room, each room can hold about 31 people normally with about 1 personal device per person.
Is this enough to cause interference, and it be enough to prevent employees from connecting and staying connected while Miracasting from their laptop to a television that supports it?

I do apologize for the 4000+ characters in the attachment.

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Posted by Kevin Blondin
Answered on November 27, 2019 1:24 am

Hi Trinity,

Based on the details you've provided and the description of your clients symptoms I suspect that you're running into airtime contention issues. Anytime you bring sixty or so clients into a room and ask them all to associate with a single AP I would expect to encounter issues. Chromebooks are particularly notorious for problems like this and multicast traffic (used to stream video) has an exponentially greater impact on wireless networks than wired as well.

With that in mind I believe you would be best served by reaching out to our professional services team and requesting a comprehensive site survey. This will allow us to establish a baseline airtime consumption and noise floor for your environment. Once those are established the network design can be reviewed to account for client load/use case and to ensure clients should expect a good experience when using the network in this manner.

I do have very general suggestions I can provide but these will require significant changes to the network and I would only expect this to help mitigate the problems but not resolve them entirely.

1) 60 clients per AP is too high. It may be necessary to add a second AP per room to divide the client load or simply reduce the client count by half if we can only maintain 1 AP per room. I would expect this to have the most significant impact.

2) As multicast impacts wireless networks much more substantially than wired networks it may be necessary to segment the broadcast domain further to reduce the volume of multicast floating around. Whether or not this is contributing to issues currently I can't say without getting to review but this could be contributing to the problems you describe.

3) Push the usage of 5ghz 20mhz DFS channels as much as possible. DFS channels are the least used and unless the clients have a particular need for the potentially higher data rates they could achieve with a wider(40/80mhz) channel then a wider band just creates more opportunities for interference. This will be predicated on whether or not your client devices are able to associate with a 5ghz DFS channel however.

4) Lower the tx power ceiling of your AP's down to 3db. If the AP is centrally located and is only meant to serve clients in the same room as it than 3db tx power should be sufficient to cover the room (unless it's a very large room). This would help to reduce things like co-channel interference with neighboring AP's and reflections.

5) I would advise only broadcasting as few SSID's as possible. 3-5 SSID's per AP means 6-10 BSSID's per AP. My personal ideal would be only 2 SSID's if at all possible. One for guest and one for everyone else.

6) Chromebooks are notorious culprits in situations like this and one thing that can help mitigate some of the issues they cause is setting up peer to peer Chromebook updates. Again I cannot say for certain that these updates are factoring into your case without getting to see the problem live but this article from Google has a section which discusses setting up peer to peer updates for Chromebooks. https://support.google.com/chrome/a/answer/3168106?hl=en

I do want to again reiterate that these are meant to be very general suggestions or guidance for how to approach and address an issue like this. I do encourage you to speak to professional services or engage with your AM/SE on that topic so that we can get concrete resolution to these issues.

Regards,
Kevin Blondin

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