When designing a wireless network, it is very important to understand the capabilities of the clients that will be using the system. 802.11 is a two-way street. The client NIC is just as important to the performance of the system as that shiny new and expensive access point.
Consider the following:
Let’s say a home user purchases the latest and greatest beast of a gaming router. This thing is so fast, it has an antenna configuration that looks like a Nazgûl crown complete with ominous red lighting. This incredible tri-band system boasts 5334 Mbps throughput for an unparalleled gaming experience.
That same user then connects their old USB WiFi Adapter with 802.11n support to that router. What speed will they get?
… Probably 75 Mbps max. Just because the AP supports newer and faster ways to communicate does not mean that the client knows how to move data any faster. And worse, other clients connected to that same gaming router will have to wait for the aging NIC to speak its piece before they get a chance to talk.
I know this is an absurd and extremely obvious example for my regular audience, but I wanted to illustrate a point. Not all devices are created equal. We care about wireless technology because that’s what we do. But many manufacturers are less concerned about 802.11 and use very “budget” wireless NICs in order to cut down on costs. I think it’s very important to be aware of the impact that a client device can have on your system – and know how to design your system with that in mind.
It’s rare in my experience to encounter a network where the clients are completely under the jurisdiction of the IT department. In a “BYOD Blend” environment, you have to design for the least capable client and hope for the best.
But let’s say that your customer wants to support general connectivity AND they need to support critical voice communications with a specific model of a phone across the campus? That gives you something more to work with.
When checking client capabilities I recommend, at a minimum, verifying the following:
- 802.11 standard support (a, b, g, n, ac)
- Support for DFS channels
- Transmission strength
- Fast Basic Service Set (BSS) Transition capabilities
- Wi-Fi Alliance certifications (WMM, WMM-AC, WMM-PS, etc)
Finding out the 802.11 standard support is easy enough… but the more granular information is not always listed in the datasheet. There are two easy ways to find details:
First, find the FCC ID. It should be clearly printed on the device. For example, here’s a snapshot of the FCC ID of my Macbook Pro:
Once you have the FCC ID, go to www.fcc.io and type it in to pull up FCC documentation on the chip.
This will pull up a LOT of documentation – more than you may ever need. Click on the “Display Grant” icon (looks like a blue checkmark) to pull up the transmit power information.
From here you can see the license that the FCC gave this specific device that governs its approved operations in different frequencies.
Notice that the transmit power can vary depending on the channel selected.
If you are having trouble deciphering the different frequency ranges, here’s a quick guide for reference:
- 5.170 to 5.250 GHz – U-NII-1 – Channels 36 to 48
- 5.250 to 5.330 GHZ – U-NII-2, Channels 52 to 64 (DFS)
- 5.490 to 5.730 GHZ – U-NII-2e, Channels 100 to 144 (DFS)
- 5.735 to 5.835 GHz – U-NII-3, Channels 149 to 165
CAUTION – not all devices will support channels in U-NII-2 or U-NII-2e. In order to use this range, the client must support DFS, or 802.11h. This is to allow coexistence with critical systems that use the same frequencies like Terminal Doppler Weather Radar. For a great talk by Devin Akin that goes into a deep dive around using DFS channels in your environment, go here.
Be careful with channel 165. This was only recently added to U-NII-3, and as a result many older clients do not support it. For a good example of how this can burn you, check out this blog.
So why do we care so much about transmit strengths? Well, a conversation doesn’t go well when one party is shouting and the other is whispering – and many devices these days whisper. Try to set your AP transmit power close to the power of your clients if you can. Both the clients and the APs have to be able to hear each other.
Now that we’ve taken a good look at the information FCC provides and determined transmit strengths, it’s time to grab some more details from the Wi-Fi Alliance Product Finder. The Wi-Fi Alliance is a non-profit organization that certifies products for interoperability in an attempt to ensure that everyone is able to communicate effectively. As a result, their product database can be very useful.
As an example, I’m going to do a search for a Cisco 8832 phone in their product finder.
That search brings up the following:
Bam! Here’s where we can find even more information about the device. Now we can really see what we’re going to be working with. You have two options here – a PDF with all the details (lower left button) and a quick popup summary (lower right button). If you open the popup window, you can see that this phone supports WMM and both WPA2 Personal and WPA2 Enterprise. That’s good.
But if you want ALL the details, you can download the certificate as a PDF then scroll down to the second page. Here you can see that the phone supports 802.11h (meaning that we can use DFS channels in our design), it has one spatial stream, it’s capable of working with 256-QAM, and a lot of other good stuff. Covering what each of these acronyms mean for your network would be far beyond the boundaries of good taste in a blog, but if you’re interested in learning more I’d recommend these two resources:
- CWNA Study Guide (Caution, a new version is on the horizon at the time of this blog post. Keep an eye out for the CWNA-107 study guide)
- 802.11ac Survival Guide This is a great resource, but it is quite technical. If you’re new to wireless I would start with the CWNA study guide instead.
The infrastructure is only half the equation in a wireless system. If you have any questions about the ramifications of what you find from these two useful sites, please feel free to reach out to me.
Packet Wrangling 