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Wireless Basics - 1

Wireless Basics - 1#



IEEE & Wi-Fi Alliance#


Institute of Electrical & Electronics Engineers

  • creates standard
  • like:
    • 802.15.1 (BlueTooth)
    • 802.15.4 (Zigbee)
    • IEEE 1394 (FireWire)
    • 802.3 (Ethernet)
    • 802.11 (Wi-Fi)

Wi-Fi Alliance#

Composed of major players in the wireless industry/space

  • Apple
  • Comcast
  • Sony
  • Motorola
  • Intel
  • Qualcomm
  • T-Mobile

Provides branding for Wi-Fi

  • "Wi-Fi"
    • 802.11i
  • WMM
  • Wi-Fi 6

Ensures interoperability between diff vendors

Wi-Fi Frequencies#

2.4 GHz & 5 GHz#

  • unlicensed spectrum
.-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.
   '-'   '-'   '-'   '-'   '-'   '-'   '-'   '-'   '-'

2.4 GHz Band#

  • low freq
    • punch stuffs
    • tend to attenuate
  • longer wavelength
    • 4.9 inch long
  • more range
    • 300 ft ?
  • more crowded
  • more non Wi-Fi interference
  • 802.11b/g/n/ax

5 GHz Band#

  • higher freq
  • shorter wavelength
    • 2.5 inch long
  • less range
    • 90 ft ?
  • less crowded
  • less non Wi-Fi interference
  • 802.11a/n/ac/ax

Q. Can a Wi-Fi adapter support multiple bands?
Yes, depends on capabilities. Its called Dual-band.

Wi-Fi History#

Major 802.11 Amendments#

Q. Band vs Channel?
Within these (2.4/5) Wi-Fi frequency bands, we have smaller bands which are referred to as Wi-Fi channels. A Wi-Fi channel is the medium through which our wireless networks can send and receive data. For routers made in the U.S., the 2.4 GHz band has 11 channels and the 5 GHz band has 45 channels.

Q. Why should I care what Wi-Fi channel I'm on?
The reason that certain channels aren't the best choice to use is because they have interference. There are a couple different ways this interference is caused: Co-Channel interference results when there are numerous devices all competing for time to talk on the same channel. Adjacent-Channel interference occurs when devices from overlapping channels are trying to talk over each other.

Channels that have interference from other devices are considered to be 'crowded'. The time it takes to transmit data is increased and you are left waiting for your Internet request to be made. The channels with the most interference are those that overlap with each other.

To further explain channel overlapping, let's look at the 2.4 GHz band, where each channel is allotted 20 MHz and separated by 5 MHz. Considering the 2.4 GHz band is only 100 MHz wide, the 11 channels of 20 MHz overlap with one another. This is what causes the interference on your network and and a lag in your Wi-Fi's performance.

Certain channels yield better Wi-Fi performance than others because they are non-overlapping. Yes, there are some channels in the 2.4 GHz spectrum that don't overlap with the other channels. These are the channels you ought to look for, especially if experiencing Wi-Fi problems: Channels 1, 6, and 11.

Read more: 1. 1.

Note: There are also 24 non-overlapping channels in the 5 GHz band spectrum.

2.4 GHz Band Channels#

  • 20 MHz wide
  • 11 channels

Q. Different Country vs Channels? Possible?
Yes. Europe has 12,13 as well. Japan has 14 as well.

Wi-Fi 2.4 Ghz and Interference#

Wi-Fi Adjacent Channel Interference#

STAs on overlapping channels will corrupt each other's transmission.

Half Duplex Wi-Fi#

Only one device can transmit on a channel at a time.

Ethernet cables are made up of multiple twisted pair of copper, they MUX. They can talk & listen at the same time.

Co-channel interference#

Slow devices on the channel consume more airtime.

2.4 GHz Channel Re-Use#

But avoiding interference in 2.4GHz is hard due to high range.

NOTE: Mist use channels 1,6,11 world-wide. (btw, they support all)

Wi-Fi 5 Ghz#

Wi-Fi 5 Ghz Channels#

  • lot more channels
  • thus lot more throughput

Wi-Fi DFS#

Dynamic frequency selection

If detected radar, move to other channel. Announce to move other APs as well.

Wi-Fi Channel Bonding#

haha typo.

haha typo again.

5 GHz Channel Re-Use#

Channel reuse is much easier in 5 GHz band.

Wi-Fi Signal Strength#

Unit/repr: dB and dBm for absolute values.

dB quantifies the ratio between two values, whereas dBm expresses the absolute power level. dBm is an absolute unit, whereas dB is a dimensionless unit. dBm is always relative to 1mW, while dB is expressed in watts and can be relative to other powers.

the unit is logarithmic & not linear, so lets see 3 & 10 rule for simiplicty:

Isn't there something in positive scale? Yes, mW. :D LOL! see the figures in mW.


# for streaming results
watch -n1 iwconfig


  • 128 clients per SSID per radio is a kind of hard limit amongs different vendors
  • ~30 clients per SSID per radio is a kind of best practice to avoid poor bandwidth

Other Wireless Technologies#

Bluetooth Low Energy (BLE)#

Wi-Fi NICs vs Ethernet#

SNR and Data Rates#


How much signal above the background noise.

Unit: dB

Data Rate#

The same "Maximum Signaling Rate". Defined per standards 802.11xyz. Unit: Mbps

Good the SNR, Can choose/set higher Data rates.

Q. Signaling Rate vs Throughput?


Modulation and Coding scheme.



Network Packets vs Frame#


Wi-Fi Frame Types and Timing#

STA (Station): In IEEE 802.11 (Wi-Fi) terminology, a station (abbreviated as STA) is a device that has the capability to use the 802.11 protocol. For example, a station may be a laptop, a desktop PC, PDA, access point or Wi-Fi phone.

Airtime Arbitration Process#

How wireless devices decides, who's going to talk next?

Wi-Fi Roaming#

Wi-Fi Security#

Ethernet is a bounded medium, inheritently & physically secure. What about security of unbounded Wi-Fi?

A Wi-Fi adapter in monitor mode can eavesdrop.. can capture all the packets nearby.. hmm..

What Mist supports today:

  • WPA-2/PSK with passphrase
  • WPA-2/EAP (802.1X)
  • Open Access
  • WPA-2/PSK with multiple passphrases
  • WEP
  • Multi-mode/PSK with passphrase
  • Multi-mode/EAP (802.1X)
  • OWE Transition
  • OWE
    • Opportunistic Wireless Encryption
  • MAC address authentication by RADIUS lookup


Every client device has its own green diamond. :D Some can roam, some are not designed to roam.

Wi-Fi Design#

How to design a wireless network? Probably for a customer.. :p

Determine requirements#

Client channel support#

Some devices might not support some channels, so plan accordingly.

Ref: (Mike - Our OpenConfig guy, from Wireless N/W Team, Google) ;)

Further Define Metrics#

Wi-Fi Ekahau Design#

Software to design a Wireless network.