CTS 156: 802.11 Service Sets

802.11 has different topologies to be aware of.  They describe how 802.11 radios may be used to communicate with each other. Many are familiar with the most common ones such as BSS and ESS. But additionally, a client can operate in an IBSS, PBSS, and MBSS.

  • IBSS: Independent Service Set
  • BSS: Basic Service Set
  • ESS: Extended Service Set
  • PBSS: Personal Service Set
  • MBSS: Mesh Basic Service Set
  • QBSS: QoS Basic Service Set

What is a Basic Service Set?

The BSS is the foundation of a WLAN. It is the most common 802.11 topology. The BSS is 1 AP with one or more client stations associated. The BSA (Basic Service Area) is the coverage area of an AP.

SSIDs have a unique BSSID. The BSSID is a MAC address of the AP’s radio of a particular SSID. The SSID is advertised in beacons (here’s a BSS!)

The 802.11 standard references BSS in various ways

  • HT BSS
  • HEW BSS (802.11ax)

Clients move between BSAs as they roam, negotiating rates dynamically as RSSI and SNR changes. There is no sharp cutoff of a BSA as it depends on external factors.

What is an ESS

It is the Extended Service Set. Or multiple BSSs with the same SSID (ESSID) connected to the same infrastructure. An example would be running a WLAN for an entire campus or running WLAN for a large office. Clients roam from one BSS to another within the same ESS

Overlap of BSA is for roaming. Hopefully, efficiently done with Fast BSS (802.11r)


The Independent BSS. Sometimes, but not often, you aren’t connecting to a ESS. It is a basic WLAN consisting of only two clients. An ad hoc network created by, for example, a laptop.

Another client, say a laptop or tablet, communicates directly with the other client. It consists of clients that are directly connected which, technically, there is only one BSS.

There is no AP, just client radios. The BSSID is randomly generated by the first station which setup the IBSS


The Personal BSS. Similar to IBSS but for DMG (Directional multi-gigabit) – 60GHz and clients communicate directly with each other. One client will be a PBSS control point (PCP).

PBSS is established through DMG clients. DMG is 802.11ad (directional multi-gigabit), commonly in mmWave


The Mesh BSS. All clients in an MBSS establish links with neighboring clients. They determine hop capabilities.

An AP can both provide connectivity to clients and be a client of another AP to provide a mesh backhaul connection. There are a lot of consumer APs using mesh.


The Quality of Service Basic Service Set. Simply a BSS that implements QoS.

Any enterprise AP manufactured in the past 10 years supports QoS, therefore, each BSS in most enterprise deployments is considered an QBSS.

CTS 155: Security beyond the fi

Security is much more than protecting the wireless frames over the air. We must also protect the infrastructure side, have proper segmentation, and ensure the right role based access. In this episode we speak with Chris Hinsz about security beyond Wi-Fi.

Securing wireless is much more than encryption. We have WPA2, upcoming WPA3 and OWE. But that’s done over the air and with 802.1X.

It goes beyond and into worrying over insecure IoT devices, stolen credentials, compromised employee devices, and more. These are all real security threats which have nothing to do with over-the-air encryption.

In this episode we talk about these security concerns and the pieces needed to secure wireless further:

  • Zero Trust Model
  • Strong segmentation
  • Multi-factor authentication
  • Indication of compromise
  • IoT Visibility

Links and Resources

CTS 153: Recap of 2018 & Starting 2019

We made it to the end of 2018! In our final episode of the year, we wanted to recap the show and its top episodes. There are some good episodes to listen to or if you already have, listen to them again!

Additionally, we wanted to share some brief stats about the show and how we’ve grown. Then we’ll share about what’s to come in 2019 for Clear To Send.

Top 10 Episodes of 2018

1 – CTS 137: MIMO
2 – CTS 106: 802.11ax with Broadcom
3 – CTS 108: Useful Wi-Fi Metrics To Track
4 – CTS 109: Ekahau Sidekick, Spectrum Analysis, & Finnish Rap
5 – CTS 123: Design Principles for Stadium Wi-Fi
6 – CTS 130: RF Characteristics
7 – CTS 107: What’s The Purpose of Cisco CleanAir
8 – CTS 138: CWNA with Coleman and Wescott
9 – CTS 134: Understanding the 4-Way Handshake
10 – CTS 125: 802.11 Frame Captures for Windows

Some stats:

  • 52 episodes for this year!
  • Now over 14k downloads per month
  • 4900 downloads in January 2018

Top countries:

  • 1 – US
  • 2 – UK
  • 3 – Australia
  • 4 – Portugal
  • 5 – Canada

Looking into 2019:

We are looking at providing some sort of Deep Dive into topics. Some of the content involved would include examples from real world data, how tests were performed, and the results we learned from the Deep Dive.

Additionally, we will look at including some video content to supplement the audio podcast.

When it comes to video, we may plan on doing a few webinars to answer questions from the listeners.

Links & Resources

Please take 5 minutes to fill out the listener survey

We’re nominated for the IT Blog Awards! Last day to vote for Clear to Send is January 4th, 2019. Please VOTE!

CTS 152: Naughty or Nice Wi-Fi

Does your Wi-Fi network make the Naughty or Nice list this December? Go through our top 5 bad and good checklist.