Introduction to Wireless LAN

Nowadays, there are about more wireless than wired devices. About 10 years ago, most offices only had desktops and some other network devices like printers. All of these were connected with wires. Today, a lot of users have a laptop, smartphone, and tablet. That’s three wireless devices for each user. Wireless speeds have increased significantly, getting close to wireless Gigabit.

IEEE uses 802.11 for all protocols that are related to wireless. Most of us have seen or heard about 802.11a, 802.11b, 802.11g, 802.11n and/or 802.11ac before. We also have the Wi-Fi Alliance that helps with the promotion of wireless networking. For example, IEEE has described authentication and encryption in their 802.11i standard. The Wi-Fi alliance has based WEP, WPA, and WPA2 on this standard. These names are easier to work with than referring to 802.11i.

SOHO Wireless LAN

Your router at home probably has the same capabilities as the one below:

soho router

It is connected to your ISP through cable or DSL, or perhaps fiber. It has some Ethernet ports to connect your computers and it has antennas for wireless users. In reality, these components are all built into one device:

  • Ethernet Switch
  • Wireless Access Point
  • (Cable or DSL Modem)
  • Router

If you take everything apart, it looks like this:

soho router roles

In small networks like this, the AP does everything by itself. We call this an autonomous access point. It uses 802.11 protocols to talk with the wireless clients and uses Ethernet on the LAN side.

Enterprise Wireless LAN

When we look at large Enterprise networks, a single access point is not enough. Imagine a network with hundreds or thousands of users. When you walk around the office, you don’t want to get disconnected every time when your phone switches from one access point to another. You want to have a stable wireless connection, wherever you go. Switching seamlessly switching from one access point to another is called roaming.

A single access point also has limited bandwidth. If you have a meeting room with 100 users then a single access point might be unable to provide enough bandwidth for everyone.

Since we use wireless networking for our users, it has to be close to our users. That’s why you will find access points on the access layer of your network, just like your computers and printers:

enterprise network wireless access points

There’s still one issue. Let’s say you are connected to an access point and you start walking around the office, your phone will switch to another access point. How does this second access point know that you are already authenticated to the network? You could re-authenticate but that will break your connection…not a good idea.

To solve this issue, we work with wireless LAN controllers:

enterprise network wireless controller

All management tasks are moved from the access points to the wireless LAN controller. It takes care of authentication, roaming, creating new wireless networks etc. The access points are only responsible for forwarding traffic, we call these LWAPs (Light Weight Access Point).

To achieve this, all traffic has to be sent from the access points to the wireless LAN controller. This is done by tunnels called CAPWAP (Control And Provisioning of Wireless Access Points). The green dotted lines are the CAPWAP tunnels between the APs and WLC.

We now have one big wireless network. If you create a new wireless network (SSID) then it will be pushed to all access points. Roaming is also no problem since all traffic is forwarded to the WLC.

Conclusion

You have now learned the basics of Wireless LANs:

  • The SOHO router is a switch, router, access point and (optionally) modem all in one device.
  • The access point is called an autonomous access point since it does everything. Wireless authentication, forwarding traffic between the LAN / Wireless LAN, etc.
  • Enterprise wireless LANs use a WLC (Wireless LAN Controller) and LWAPs (Light-Weight Access Point).
  • Management tasks like creating wireless networks, authentication and roaming is all done in the WLC. The LWAPs are responsible of forwarding wireless traffic to and from the LAN.
  • The WLC and LWAPs allow us to create a big, scalable wireless network.

Forum Replies

  1. Hello Abhishek

    Let me answer your second question first: Yes, the APs connect via a physical cable to the Access Layer switches.

    Concerning your first question, don’t confuse the terms ACCESS point and ACCESS layer switch. They have different meanings. An Access Layer switch is a switch that resides on the access layer of the three tier network design model: Core, Distribution and Access. The access layer of this model is the portion of the network that connects to the end devices such as phones, PCs, access points and so on. (For more information about th

    ... Continue reading in our forum

  2. Hello Rene,

    Could you please let me know what is your suggestion for a good book for wireless (Beginner to intermediate level)? Thanks in advance.

  3. Hi Wisam,

    I can highly recommend all the CWNP material. CWNA is the “beginners” material. Take a look at this book:

    CWNA: Certified Wireless Network Administrator Official Study Guide

    It’s vendor neutral and explains all the L1/L2 wireless stuff in detail.

  4. Thanks Rene,
    I got it 2 days ago and it’s really good book.

    Thanks a lot again Rene!

  5. Good to hear you like it!

    If you want to look at wireless frames, keep in mind that Wireshark on Windows doesn’t show 802.11 frames. Most windows drivers for wireless adapters don’t support “monitor mode”. If you want to look at 802.11 frames, the best thing to do is to download Kali and use one of the supported wireless adapters:

    http://www.wirelesshack.org/best-kali-linux-compatible-usb-adapter-dongles-2016.html

    These support client mode, monitor mode but also packet injection which is great if you are diving into WEP/WPA(2) security and other wireless attacks.

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