Network Fundamentals // Lesson 07

Wireless
fundamentals.

Wi-Fi uses radio instead of copper or fibre, but it still connects users into the same underlying network. In this lesson you'll learn about SSIDs, access points, wireless frequencies, channels, interference, roaming and the basic journey of a wireless client.

📖 Beginner ⏱ About 15 minutes ✓ Quiz included CCNA 200-301
01 // Wireless network

What makes up a Wi-Fi network?

📱

Wireless Client

A laptop, phone, tablet or other device using an 802.11 wireless interface to communicate with an access point.

📡

Access Point

Provides wireless connectivity and bridges client traffic into the wired LAN.

🎛️

Wireless Controller

Can centrally manage wireless configuration, access points, WLANs and other aspects of a larger deployment.

An access point is not simply a wireless router. In enterprise networks, the AP commonly bridges wireless traffic into VLANs on an existing switched network.
02 // WLAN identity

SSID identifies the wireless network

The Service Set Identifier, or SSID, is the familiar wireless network name shown to users.

SSID

Human-readable wireless network name presented to users.

Baznetic-WiFi

VLAN

An SSID can map client traffic into a particular wired VLAN.

Baznetic-WiFi → VLAN 20
SSID and VLAN are not the same thing. The SSID identifies the wireless network; the VLAN provides Layer 2 segmentation on the wired network.
03 // Radio frequency

2.4 GHz vs 5 GHz

2.4 GHz

Longer reach, fewer channels

  • Generally greater range
  • Better penetration through obstacles
  • Fewer non-overlapping channels
  • More likely to experience interference
  • Shared with many non-Wi-Fi devices
5 GHz

More capacity, shorter reach

  • More available channels
  • Often less congested
  • Supports higher-capacity deployments
  • Typically shorter effective range
  • More affected by walls and obstacles
Higher frequency does not automatically mean "faster Wi-Fi". Actual performance depends on the Wi-Fi standard, channel width, signal quality, interference, client capability and network design.
04 // Channels

Wi-Fi shares the air

Wireless devices use radio channels. Poor channel planning can cause networks to compete for airtime or interfere with one another.

In the 2.4 GHz band, the commonly taught non-overlapping 20 MHz channel plan uses:

1 2.4 GHz channel
6 2.4 GHz channel
11 2.4 GHz channel
Channel availability varies by regulatory domain. For CCNA, the important concept is understanding channel overlap and interference.
05 // RF behaviour

Wireless signals are affected by the environment

Attenuation

Signal strength decreases as the signal travels farther from the transmitter.

Absorption

Materials such as walls and other objects can absorb RF energy and weaken the signal.

Reflection

RF signals can reflect from surfaces, producing multiple signal paths.

Interference

Other transmitters or electronic devices can make successful communication more difficult.

Signal-to-Noise

Good wireless performance depends on the useful signal being sufficiently stronger than background noise.

Distance

Clients farther from an access point generally have weaker signal and may use lower data rates.

06 // Client connection

How does a wireless client join?

At a high level, a client discovers available wireless networks, associates with an access point and completes any required security authentication.

📱
Client

Discovers available WLANs

→
📡
Access Point

Association and security

→
🌐
Network

Client traffic enters the LAN

07 // SSID vs BSSID

One wireless name can have many AP radios

In an enterprise wireless network, many access points may advertise the same SSID.

SSID
The network name users recognise, such as Corporate-WiFi.

BSSID
Identifies a specific basic service set and is associated with a particular AP radio/interface.

Multiple access points can advertise the same SSID while each radio has its own BSSID.
08 // Roaming

Clients can move between access points

Enterprise networks often deploy multiple access points with the same WLAN configuration so users can move around a building while remaining connected.

The client ultimately makes important decisions about when to move from one access point to another, although infrastructure features can help make roaming smoother.

More APs does not automatically mean better Wi-Fi. AP placement, transmit power, channel planning and client behaviour all matter.
09 // Wireless security

The air is a shared medium

Unlike a physical Ethernet cable, wireless signals can extend beyond the room or building where the network is installed. Authentication and encryption are therefore fundamental parts of wireless design.

WPA2 / WPA3
Modern wireless security standards used to protect WLAN traffic.

Personal mode
Often uses a shared passphrase.

Enterprise mode
Commonly uses individual authentication through 802.1X and an authentication service such as RADIUS.

10 // Practical thinking

A wireless problem isn't always a network problem

Imagine a user can connect to the SSID but complains that Wi-Fi is slow. Before blaming DHCP, routing or DNS, consider the RF environment.

Is the client far from the access point?

Is the signal passing through several walls?

Is the channel congested?

Are neighbouring APs using poor channel assignments?

Is there non-Wi-Fi interference?

Is the client connected to the expected band and access point?

Wireless troubleshooting adds RF to the normal network stack. A perfectly configured IP network can still provide a terrible user experience if the radio layer is poor.
11 // Check your knowledge

Quick quiz

1. What does SSID identify?

The SSID is the identifier or name presented for a wireless LAN.

2. Which device normally bridges wireless clients into the wired LAN?

The wireless access point provides 802.11 connectivity and bridges client traffic into the LAN.

3. Which set represents the commonly taught non-overlapping 2.4 GHz channels?

Channels 1, 6 and 11 are the familiar non-overlapping 20 MHz 2.4 GHz channel plan commonly taught for CCNA.

4. Which frequency band generally provides better propagation and longer reach?

Lower-frequency 2.4 GHz signals generally propagate farther and penetrate obstacles better than 5 GHz signals.

5. What is a BSSID associated with?

The BSSID identifies a specific basic service set and is typically associated with an individual AP radio/interface.

6. Which statement about 5 GHz Wi-Fi is generally correct?

5 GHz generally provides more channel options and capacity, while its propagation range is typically shorter than 2.4 GHz.

7. Which of these can negatively affect wireless performance?

Signal attenuation, interference and poor channel planning can all degrade wireless performance.
Score: 0 / 7
Lesson complete

Next: Virtualisation & Network Architecture

One final Network Fundamentals lesson to go. Next we'll look at virtual machines, virtual switching, containers, cloud networking and the architectural ideas that make modern networks look different from a traditional rack full of physical servers.