802.11 Service Set

Course Contents

1. What are 802.11 Service Sets ?

The 802.11 standard defines different types of service sets, which are groups of wireless devices working together to communicate.

There are three main types of service sets:

Independent Service Set (IBSS)
Infrastructure Service Set
Mesh Basic Service Set (MBSS)

All devices in a service set share the same SSID (Service Set Identifier)—the network name you see when searching for Wi-Fi connections.

Smartphone screen showing Wi-Fi settings with 'Home Wi-Fi' network selected, illustrating an example of an SSID in an 802.11 service set.

📢 Now, let’s explore each of these service sets in detail so you can understand how they work.

2. Independent Basic Service Set (IBSS)

For the first type of service set, we have the IBSS (Independent Basic Service Set), which is a wireless network where devices connect directly to each other without an Access Point (AP).

Diagram of four laptops connected in an IBSS ad hoc network without an access point, illustrating direct wireless communication between devices.

💡 This type of network is also called an ad hoc network.

A great example is AirDrop when you send a file from one iPhone to another, the devices form a direct wireless connection without needing a router or Wi-Fi network.

What makes an IBSS special?

Direct device-to-device communication—no access point needed.
Perfect for quick, temporary tasks, like file transfers (AirDrop, Wi-Fi Direct, etc.).
Not ideal for large networks—it works best with just a few devices.

💬 If you’ve ever shared files between two phones without using Wi-Fi, you’ve already experienced an ad hoc connection!

3. Infrastructure Service Set

Now, let’s explore the second type of service set: the Infrastructure Service Set. In this setup, devices connect through an Access Point (AP) instead of communicating directly with each other.

This is the most common Wi-Fi setup, used at home, in offices, and in public places.

Depending on the number of APs and how they are deployed, there are two main configurations:

Basic Service Set (BSS)
Extended Service Set (ESS)

Basic Service Set (BSS)

A BSS (Basic Service Set) is when all devices communicate through a single AP, as shown below:

Each AP has a unique identifier called the BSSID, which is its MAC address.

How Does Traffic Flow in a BSS ?

Unlike in an ad hoc network, devices in a BSS cannot communicate directly with each other. Instead, all data must pass through the AP, even if two devices are physically close to each other.

Diagram of a Basic Service Set (BSS) showing laptops communicating through an Access Point (AP) with SSID PingMyNetwork and BSSID MAC address; direct laptop-to-laptop communication is not allowed.

📢 For example, if one laptop wants to send data to another, it must send it to the AP first, which then forwards it to the other device.

Diagram of a Basic Service Set (BSS) showing devices communicating via an Access Point (AP) with SSID PingMyNetwork and BSSID MAC address; data must pass through the AP to reach another device.

Extended Service Set (ESS)

Sometimes, one AP isn’t enough to cover a large area.

An ESS (Extended Service Set) allows you to extend the range of your Wi-Fi network by using multiple APs that work together.

Diagram of an Extended Service Set (ESS) with two overlapping Basic Service Sets (BSS1 and BSS2), each with an Access Point (AP) sharing the same SSID but different BSSIDs, allowing wider Wi-Fi coverage.

What makes ESS special?

The best part is that APs in an ESS can share the same SSID !

: "Extended Service Set (ESS) diagram showing two overlapping Basic Service Sets (BSS1 and BSS2) with Access Points (APs) sharing the same SSID, illustrating device roaming between APs.

Roaming: Moving Between APs

Roaming is when your device moves from one AP’s coverage area to another and seamlessly connects to the next AP.

💡 To ensure smooth roaming, the coverage areas of the APs should overlap by about 10-15%.

4. Mesh Basic Service Set (MBSS)

A Mesh Basic Service Set (MBSS) is a type of Wi-Fi network where APs communicate wirelessly instead of using cables.

APs relay traffic to the wired network

In this network, there are two types of APs:

RAP (Root Access Point) → Connected to the wired network.
MAPs (Mesh Access Points) → Connected wirelessly to the RAP and to each other.

Unlike traditional Wi-Fi, where each AP needs a cable, MBSS extends coverage wirelessly.

5. Distribution System (DS)

Your wireless infrastructure needs to be connected to your wired network. The Distribution System (DS) is the wired network that connects APs to the rest of the infrastructure.