The “Magic” of Wireless Mesh

This document is also available for download via a PDF White Paper.

The Wireless Mesh Cost vs Throughput Spreadsheet.

 

The “Magic” in magic is really just a combination of illusion and mis-direction.  And yet we are entertained by being convinced we’ve seen something that breaks known physical laws.

We know the woman really isn’t being sawn in half, yet we don’t mind suspending reality for a couple of minutes while we try and figure out how the magician is doing his magic.

In the world of Wireless Mesh, sometimes WLAN professionals get too caught up in the mis-direction and illusion of getting something for nothing that we forget all about the laws of physics that determine connections and throughput and watch as our customers suspend reality hoping to get something for nothing, and not paying any penalties.

In reality, there is nothing “magic” about Wireless Mesh. It follows known laws concerning RF propagation, packet transfers, and network packet protocols.

I believe that Wireless Mesh does have it’s place in WLAN Design… but many people, in their quest to save a bit of money end up ruining their Wi-Fi network by employing mesh incorrectly.

To emphasize this point, I’ve developed an Excel Spreadsheet and made it available to download. (Link to Mesh Analysis Spreadsheet) – this spreadsheet, like all good spreadsheets, pulls the variables out where you can see them. All the fields colored in Green are the input points for the algorithms. You, as a WLAN designer can choose your own amounts for these.

Here are the variables you can enter to drive the equations in the Spreadsheet:

  • Expected net TCP data rate on the 2.4GHz Access Frequency
    • I started using a value of 25Mbs to reflect a network where the bulk of the client devices are still 802.11g
  • Expected net TCP data rate on the 5GHz Mesh Frequency
    • This is estimated at a value consistent with an 802.11n connection
    • Remember – the Mesh AP’s must be within range to have great SNR to maintain this data throughput!
  • Number of Clients per 2.4GHz Access Point
  • Cost of a wired Ethernet Backhaul connection
    • Including Cat 5e cabling, installation, and cost for a switch port
  • Sample Size of the Mesh Network
    • number of Access Points to provide coverage for clients, as well as enough Mesh AP’s to maintain high throughput speeds between 5GHz Mesh RF connections.
  • Average Loss in Percentage per additional Hop.
    • I’ve started with the minimum loss of 50%, in actuality there could be 10% to 15% more loss because of overhead and other issues.
802.11g 2.4GHz dedicated to Access

25

Mbs
802.11an 5GHz dedicated to Mesh

75

Mbs
Number of Clients per Access Point

25

Clients/AP
Cost Per Access Point – Installed

$600

/AP
Cost per wired Backhaul Connection

$400

/Cable Drop & Switch Port
Sample Size of Wireless Mesh Network

50

Access points
Average Loss per each additional hop

60%

% loss

 

Remember, you are the one to make these assumptions. This is not something that I’m making up – you put in your actual costs, size of system, assumptions on data throughput and number of clients per access point.

You can use this spreadsheet to work with your customers/clients to help them better understand the value and costs of providing Wireless Mesh versus other alternatives like Ethernet cable or a dedicated Wireless Bridge.

As an aside, I like to keep these in order both in my mind, as well as in the mind of my customers. Order of AP backhaul desired:

  • Fiber
  • Copper
  • Dedicated Wireless Bridge
  • One-Hop Wireless Mesh
    • and way down here in the very last position
  • a Multi-Hop Wireless Mesh

 

Also remember the first hop is ‘free’ – only kind of – since there isn’t the requisite 50% loss on this first hop. The receiving Mesh AP doesn’t need to re-transmit the packet on the 5GHz channel. The client packet comes into AP #1 on 2.4GHz, AP #1 then re-transmits the packet on 5GHz, then AP #2 receives the packet and places it directly on it’s Ethernet port.

But for subsequent Mesh Hops, AP #2 would have to re-transmit the packet on the same 5GHz channel it came in on… thus the 50% drop (Plus additional loses due to overhead issues) Each subsequent hop also results in this drastic degradation of data throughput.

Here are some graphical examples of this process of going to multiple hops. The horizontal access is number of Mesh AP’s – one more than the Mesh Hop (two meshed AP’s equals one Mesh Hop).

Note the gradual reduction in total cost as you add more Mesh Hops. It is true that adding Mesh rather than Ethernet will save you money, but only on the installation costs, not the actual cost of the Access Point.  But also note the drastic drop in throughput as you add more hops.

In this graph we can see as the average cost per installed AP drops (savings from the Ethernet cabling costs as you go with more and more Mesh Hops) the actual cost per kilobyte for each end user skyrockets. This is a function of more and more client devices sharing less and less actual Ethernet backhaul.

In this final graph we’ll focus on comparing the savings in percentage of lowered backhaul costs, compared with the loss of throughput. The “Sweet Spot” is at two Mesh AP’s or one Mesh Hop. Each additional Mesh Hop barely adds much in the way of cost savings, but instead has a huge drop in throughput.

 

Feel free to try out this spreadsheet on your own and see how little is actually saved in adding more mesh hops, then compare the huge drop in throughput as well as it’s associated costs per Kilobyte to end users.

Learn from the experience of others, and don’t get caught with a Wireless Mesh system that doesn’t provide for the requirements of your client devices.

Wireless Mesh isn’t “Magic” – it’s merely an illusion of cost savings – you still can’t break the laws of physics.

 

(a note that I’m not talking about Strix or Firetide Wireless mesh so hold your comments on those vendor’s proprietary solutions)


 

Please note: I reserve the right to delete comments that are offensive or off-topic.

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34 thoughts on “The “Magic” of Wireless Mesh

    • In a dual-radio setup, the client’s packet leaves on 2.4GHz to the first radio in the AP. The AP then transfers this to the 5GHz radio. A little loss, but not too much. The first hop then happens when the 5GHz radio retransmits the packet to Mesh AP #2.

      The first 50%+ big loss in throughput now happens when the Mesh AP #2 retransmits the same packet it just received, on the same channel towards Mesh AP #3. This means the time for Mesh AP #2 to Receive the packet is not duplicated (used again) when transmitting this packet. Thus at least 50% loss.

      You are correct that A three radio Access Point could alleviate this issue by changing channels upon each hop.

      • Strix systems has one of the coolest UI and the mutiradio productline was awesome.

        I have seen it work well with 802.11a/g radios.
        Can all the radio’s of the Multiradio mesh be 802.11n ?
        Wont you run in antenna placement issue’s??

        • Sure, any radio can be 802.11n if the vendor provides it. And with WiFi, or any other wireless technology, there are ALWAYS antenna placement issues. It is something that all WLAN pros should strive to be experts at.

          • Hi Matt,

            I was talking about Multi-radio Mesh equipped with 802.11n  (2*2:2)  .In a 6  radio stack it would sum upto 12 antennas.Min .

            Antenna placement issues faced with Single radio AP is  diffrent than the one with Radio stacks .IT IS NOT THE SAME

            I was just trying to understand how viable it is ..
            Is the usage of combiners the only go???
            Please educate

          • Whether 2×2 or 3×3, you can use modern antennas that encase multiple antennas in a single enclosure. So it’s not that bad of a problem. But yes, antenna placement is always an issue in any wireless network. 

            And as for Mesh vendors that support “true” multi-radio, multi-channel mesh, let’s count. Cisco, Strix, Firetide, Bel Air, Aruba, Mikrotic and I’m sure I’m missing a few. Can someone add up the vendors who call their solution Mesh, but it’s really repeater mode radios? 

    • Evert, you are correct. A true mesh is multi-radio and doesn’t not suffer any degradation per hop. What Keith should have called this is a bridge/repeater network. It’s not mesh.

      • Matt, I like your definition of a “True” mesh changing channels on each hop. That is great for Strix customers – but the majority of Mesh vendors use one frequency for Access – usually 2.4GHz and the other frequency 5GHz for the Mesh backhaul. (all Mesh AP’s sharing the same channel for the Mesh frequency)

        Of course changing the channel at each hop would be a much better solution… but not all vendors offer that.

        Thanks for your comments.

        • I would argue that most mesh vendors nowadays offer true multi-radio mesh. They have seen the light and modified their offerings. Also note that Strix, and maybe Firetide, as well as Aruba and others do not use proprietary solutions. It is standard 802.11 and 802.3 inside the box. 

          • Matt,

            Thanks for your comments and additions to the blog. I appreciate your expertise on Mesh.

            Just having multiple radios in the box won’t keep you from the throughput drop mentioned in the white paper. It is the ability to change channels at each Mesh hop rather than having a single Mesh frequency that leads to the throughput savings.

          • I am sorry to have to correct you again Keith. A true mesh does not suffer from a throughput drop. And even more importantly it doesn’t suffer from any significant added delay (important for VoIP). Thus the points published above are simply not correct for a true multi-radio mesh. 

          • No worries. I’m agreeing with you about “True Mesh” – no throughput loss there.

            I’m just saying most mesh vendors today are NOT “True Mesh”…

    • In a dual-radio setup, the client’s packet leaves on 2.4GHz to the first radio in the AP. The AP then transfers this to the 5GHz radio. A little loss, but not too much. The first hop then happens when the 5GHz radio retransmits the packet to Mesh AP #2.

      The first 50%+ big loss in throughput now happens when the Mesh AP #2 retransmits the same packet it just received, on the same channel towards Mesh AP #3. This means the time for Mesh AP #2 to Receive the packet is not duplicated (used again) when transmitting this packet. Thus at least 50% loss.

      You are correct that A three radio Access Point could alleviate this issue by changing channels upon each hop.

      • Strix systems has one of the coolest UI and the mutiradio productline was awesome.

        I have seen it work well with 802.11a/g radios.
        Can all the radio’s of the Multiradio mesh be 802.11n ?
        Wont you run in antenna placement issue’s??

        • Sure, any radio can be 802.11n if the vendor provides it. And with WiFi, or any other wireless technology, there are ALWAYS antenna placement issues. It is something that all WLAN pros should strive to be experts at.

          • Hi Matt,

            I was talking about Multi-radio Mesh equipped with 802.11n  (2*2:2)  .In a 6  radio stack it would sum upto 12 antennas.Min .

            Antenna placement issues faced with Single radio AP is  diffrent than the one with Radio stacks .IT IS NOT THE SAME

            I was just trying to understand how viable it is ..
            Is the usage of combiners the only go???
            Please educate

          • Whether 2×2 or 3×3, you can use modern antennas that encase multiple antennas in a single enclosure. So it’s not that bad of a problem. But yes, antenna placement is always an issue in any wireless network. 

            And as for Mesh vendors that support “true” multi-radio, multi-channel mesh, let’s count. Cisco, Strix, Firetide, Bel Air, Aruba, Mikrotic and I’m sure I’m missing a few. Can someone add up the vendors who call their solution Mesh, but it’s really repeater mode radios? 

    • Evert, you are correct. A true mesh is multi-radio and doesn’t not suffer any degradation per hop. What Keith should have called this is a bridge/repeater network. It’s not mesh.

      • Matt, I like your definition of a “True” mesh changing channels on each hop. That is great for Strix customers – but the majority of Mesh vendors use one frequency for Access – usually 2.4GHz and the other frequency 5GHz for the Mesh backhaul. (all Mesh AP’s sharing the same channel for the Mesh frequency)

        Of course changing the channel at each hop would be a much better solution… but not all vendors offer that.

        Thanks for your comments.

        • I would argue that most mesh vendors nowadays offer true multi-radio mesh. They have seen the light and modified their offerings. Also note that Strix, and maybe Firetide, as well as Aruba and others do not use proprietary solutions. It is standard 802.11 and 802.3 inside the box. 

          • Matt,

            Thanks for your comments and additions to the blog. I appreciate your expertise on Mesh.

            Just having multiple radios in the box won’t keep you from the throughput drop mentioned in the white paper. It is the ability to change channels at each Mesh hop rather than having a single Mesh frequency that leads to the throughput savings.

          • I am sorry to have to correct you again Keith. A true mesh does not suffer from a throughput drop. And even more importantly it doesn’t suffer from any significant added delay (important for VoIP). Thus the points published above are simply not correct for a true multi-radio mesh. 

          • No worries. I’m agreeing with you about “True Mesh” – no throughput loss there.

            I’m just saying most mesh vendors today are NOT “True Mesh”…

  1. In my mind, since all mesh APs need to be on the same channel, it needs to use 40MHz wide channels, which will give you at least 150Mbps of throughput (even at some significant range).  Then, dividing that in half (or slightly more) each time would yield about 3 hops before the throughput would be a bottleneck for a single loaded AP or several not-so-busy APs.

    Mesh APs should use AC power indoors, but yes, outdoors, they are often PoE powered. :) Very odd situation.

    Whether mesh is worth using, beyond 1 hop, to me, depends on how busy the access APs are, the network design itself (like distance between hops), and how the Mesh APs could be powered.

    Devinator

  2. In my mind, since all mesh APs need to be on the same channel, it needs to use 40MHz wide channels, which will give you at least 150Mbps of throughput (even at some significant range).  Then, dividing that in half (or slightly more) each time would yield about 3 hops before the throughput would be a bottleneck for a single loaded AP or several not-so-busy APs.

    Mesh APs should use AC power indoors, but yes, outdoors, they are often PoE powered. :) Very odd situation.

    Whether mesh is worth using, beyond 1 hop, to me, depends on how busy the access APs are, the network design itself (like distance between hops), and how the Mesh APs could be powered.

    Devinator

  3. Absolutely, 100%, spot on. I fight this battle with some systems integrators trying to cut a corner on EVERY project.  Mesh is good for 1 hop indoors (as a cost saving measure) and should never be deployed more than 3 hops deep or with a ratio of more than 1:5 (read Devinator’s comment) using 802.11g only APs -> 1:2.  

    Mesh impacts network capacity and user experience and you should ALWAYS account for that in the design. That said, Mesh outdoors makes good cost saving sense where Fiber Trenching, PTP links etc can be a significant cost. Good info here. Strangely, “true mesh” when deployed on indoor environments can work out MORE expensive than just ponying up and installing the cat6 and a PoE switchport.  ;-)

  4. Absolutely, 100%, spot on. I fight this battle with some systems integrators trying to cut a corner on EVERY project.  Mesh is good for 1 hop indoors (as a cost saving measure) and should never be deployed more than 3 hops deep or with a ratio of more than 1:5 (read Devinator’s comment) using 802.11g only APs -> 1:2.  

    Mesh impacts network capacity and user experience and you should ALWAYS account for that in the design. That said, Mesh outdoors makes good cost saving sense where Fiber Trenching, PTP links etc can be a significant cost. Good info here. Strangely, “true mesh” when deployed on indoor environments can work out MORE expensive than just ponying up and installing the cat6 and a PoE switchport.  ;-)