Wireless Mesh networking

[TH09]

A couple of questions to help me understand wireless mesh networking 

1. Why do the RAPs and MAPs participating in the mesh need to be on the same channel

2. If there are like 20 APs in a mesh all on the same 5 GHz channel, pretty close to each other, wouldn't that cause channel interference on that channel? If not, why and please provide details.

3. If we are using 5 GHz for both backhaul + provide client access and also providing client access on the 2.4 GHz, is there a way to set priority (QoS)? So for example, I want to provide a higher priority to my clients on the 2.4 GHz than 5 Ghz, is that possible? If so, how or what are some of the best ways to tackle situations like these? 

4. In a mesh topology with RAPs connected to multiple MAPs, if the mesh channel goes bad (any interference device causes channel interference), is there a way the RAP automatically can figure out the channel has gone bad and changes the channel to a clean one (on the 5 Ghz band). Kind of like EDRRM but on the 5 GHz in a mesh.

Thanks.

TH. 

[pieterh]

1) RAP and MAP (or multiple MAPs) need to communicate with each other hence they need to be on the same channel for this

    (not the client link, that can be different) yes with increasing number of MAPs this channel gets more loaded

2) yes, but can be steered somewhat by using multiple RAP's on different channels
    divide 20 MAPS over 4 RAPs -> 5 MAP's/RAP

3) QoS is available both on 2,4GHz and 5GHz bands
   but what you describe is NOT QoS, you can set a preferred band at the client wifi adapter settings, is this what you mean?

4) (NB no life experience) I guess this is possible, but as the contact between RAP and MAP is lost when changing channel ,

    the MAP(s) needs to scan the band for the new channel used by the RAP,

    as a result it will take some time before the mesh has converged and all MAPs to this RAP use the new channel.

[TH09]

Thanks Pieterh,
3) No what I meant was say i have provided client access on both bands but I want client traffic on the 2.4 GHz given more priority over clients on the 5 Ghz.

[Scott Fella]

You need to understand the basics also. Back haul on 5ghz is to provide the best overall throughout since there is less channel utilization. That being said, 2.4ghz being over utilized, will get you poor performance and QOS will not help that at all. You need to look at the best practice for RF and mesh, not what you want to do but how it’s meant to be deployed. Then that will give you a better understanding of what you should do and what you should not do. Allowing client access on the back haul can make the experience for users very poor especially if you have a lot of clients. Also the number of hops will also give you a good idea of the performance you should expect when 2-3 hops or more away. Don’t design wireless when the manufacturer didn’t design it that way or else your end result will be something that isn’t ideal and something you will own and take accountability on.

[TH09]

Thanks for helping out Scott. That is true but their are a few very important devices for example RFID tags and things that can only run on the 2.4Ghz and should not be disturbed hence finding ways to minimize the disturbance while utilizing the mesh as much as we can and where we can.

[Scott Fella]

I understand but you can’t control what is in the air already. What you need is to have good rssi where the client devices will be along with good snr. That alone should help you. RFID doesn’t take much bandwidth but you also don’t want to impact your regular users expert. Plan our your area, use as many RAPs and. It more than 2-3 hops. I would not allow client access on the backhaul unless you have minimal client connections.

[TH09]

I ran some quick ping rate tests on rfid tags and saw the transmission dropped alot when the clients were on hence I wanted to know and find out ways to reduce the client impacts on the rfid transmissions.

[Scott Fella]

Let me try to better understand this. Is your rfid not working or are you worried because what you see during your pings? I know some devices don’t respond to pings like other devices do. Remember that wireless is half duplex and only one device can communicate at a time. So you should have a good baseline number of how many clients devices start to affect your rfid data and or your pings if they do correlate together. If your rfid is on a separate ssid, you can try to set the QOS on the ssid to provide some priority over the air. You should also reach out to the rfid manufacturer to see what settings they suggest.

[pieterh]

no, (AFAIK) there is no way to load-balance between 2,4 and 5 GHz

you can only steer this by using different SSID's

in addition you can prepare a design where you classify the area's

like production area's where 2,4 GHZ is commonly available for the RFID devices and 5GHz only on selected AP's

and office area's where 5GHz is common mostly for PC's and 2,4GHz on selected AP's (for e.g. mobiles that only have 2,4GH)