All About Wireless LAN 102: The Answers to Your Questions

by | Jun 1, 2013 | Blog

wireless-LAN | Wireless LAN Questions

Hello friends, novice learners. This week, we help uncover some of your questions about wireless LAN in hopes to give you more knowledge about wireless LAN networking, 802.11 access points, APs and lots more.

Today, here are the answers to 4 questions we thought you need to know:

1.     What is the impact of having both the 802.11g and 802.11n access points in the same environment? Will this cause conflicts for the clients in this environment? 

Whenever you have a mixed group of clients, there will need to be a way to protect them from talking on top of each other. The 802.11 protocol calls this ‘Protection Mode’ – and it allows for mixing of different types of clients. This does NOT force the .11n clients to go at .11g speeds! But it does for them to preface each data transmission with an extra frame or two to ‘clear the air’ before transmitting. This does cause some additional overhead and will slow down the newer devices. (The older devices do not need to protect themselves)
 
It is far better to have all .11n clients and .11n access points – we call this ‘Green Field’ mode. But in the real world it is fairly impractical to achieve.
Can you catalog users by the frequency?
Most enterprise-class Access Points have the ability to help ‘steer’ client devices between the two supported frequencies, from the crowded 2.4GHz range to the less-congested 5GHz frequencies. This feature is one more item that sets enterprise-class AP’s apart from their less capable, cheaper, SOHO cousins. 
 
In fact, in the 802.11ac specifications, ALL client devices MUST be capable of moving to the less-crowded 5GHz frequencies.

2.     When a company completes migration to 802.11n, what can it do to avoid coexistence problems with neighboring businesses that still use 802.11g?

Not a lot. There are no government regulations or laws that can ‘force’ anyone to move to the more efficient newer 802.11 protocols. A good RF design, with accurate placement of access points, and perhaps even use of directional antennas can help. Just adding more access points usually just results in less efficient RF spectrum. The Wi-Fi protocol is a ‘shared medium’ protocol – unlike Ethernet Switches where each device has dedicated access to the media – Access Points are more like Hubs where all AP’s and Clients on the same frequency ‘share’ the media at the same time.
 
That is why we are moving as quickly as possible to the 5GHz frequencies where we have more channels and options to choose from. The 2.4GHz space only has enough spectrum to support three channels, 1, 6, and 11 at the same time. 
 
Moving to all 5GHz capable devices would be a great start.

3.     What are the best methods for handling rogue APs?

First we have to define what is a “Rogue Access Point”? 
There are neighbors who have AP’s that show up in your client’s Wi-Fi as accessible to join. Is that a Rogue? You have no legal right to do anything with that type of Rogue – it is outside your building and just sharing the same legal frequencies. 
 
But an Access Point that you do not own, that is on your wired network, sharing it with others wirelessly – that type of Rogue is something you should track down and remove immediately. 
 
You can listen in the air for the Rogue AP’s MAC address, and then look for a like MAC in your switches CAM tables, find the switch port and remove the offending device.
 
There are commercial tools to help with this process. If you are using Enterprise-Class Access Points, many have a built-in Wireless Detection System, and even rudimentary location tracking features to help you find the Rogue.

4.     Many of our wireless devices can connect to either a cellular data network or to a Wi-Fi network. How do we make the cellular vs. Wi-Fi decision for connecting enterprise devices?

By default, your device will join the cellular network, if you want to over-ride that and force the device, you must choose a Wi-Fi network to join.

 

These are all for today. Stay tuned for more answers to your wireless LAN-related questions.