Podcast

CTS 133: 802.11 PHY Types

Let’s discuss the different 802.11 PHY types available for devices to use.

Meet Glenn Cate

Our featured wireless network engineer is Glenn Cate, CWNE #181. Catching up with Glenn at Cisco Live 2018 was great and we were able to get him talking about himself. Listen to the episode to hear a little bit about Glenn.

Glenn Cate, CWNE #181

802.11 PHY Types

The 802.11 Standard defines different PHY types. Includes the data rates supported by each PHY and what band they operate in. Data rates depend on the channel width and modulation used.

Download the free 802.11 PHY Types Reference PDF

In 1997, the first iteration of the standard was released. We call this 802.11 Prime. In this standard, the PHY type available used Direct Sequence Spread Spectrum (DSSS). It was only available in the 2.4 GHz spectrum using a 22 MHz wide channel. It offered 1 spatial stream and devices were able to use from 1 to 2 Mbps data rates.

Table of 802.11 PHY Types

802.11 PHY Types

802.11a was ratified in 2009 and operated in the 5 GHz spectrum. With this PHY, devices were able to use up to 54 Mbps data rates. Modulation used with this PHY type was Orthogonal Frequency Division Multiplexing (OFDM) and used a 20 MHz wide channel at 1 spatial stream.

802.11b, still operating in the 2.4 GHz spectrum used a modulation of High Rate DSSS (HR/DSSS) for this PHY type. It still used a 22 MHz wide channel width but offered data rates up 5.5 and 11 Mbps.

To maintain backwards compatibility to DSSS but bring improvements to 2.4 GHz was the 802.11g PHY type. The new modulation used was Extended Rate Physical OFDM (ERP OFDM). The channel width changed to 20 MHz but still saw data rates up to 54 Mbps using 1 spatial stream.

The biggest change to Wi-Fi came with the 802.11n PHY. It was dual-band and used the High Throughput (HT) modulation. It offered up to 600 Mbps data rates and introduced channel bonding to 40 MHz channel widths. Another improvement was the introduction of MIMO and 4 spatial streams.

What we’re currently used to, as of the release of this episode, is the 802.11ac PHY type. Defined as Very High Throughput (VHT) and only operating in the 5 GHz spectrum, it introduced new channel bonding at 80 and 160 MHz channel widths. This increased channel width, along with 8 spatial streams, touts up to 6.9 Gbps data rates. But don’t hold your breath.

Next up, not ratified yet as of the time of this published episode, is 802.11ax PHY type with modulation scheme of High Efficiency (HE). This brings increased efficiency in the 2.4 GHz and 5 GHz spectrum. Specifying, in this PHY type, is 1024 QAM and up to 9.6 Gbps data rates. We shall see what this brings to the real world.

Links and Resources

CTS 132 – Location-Based Analytics

Recorded at Cisco Live 2018 in Orlando, FL, we speak to Christian Gauer about Wi-Fi location-based analytics.

Meet Greg Skeene

Our featured wireless engineer for this episode is Greg Skeene. He’s a listener of the show and we finally met up during a meetup at Cisco Live. Listen to the episode to hear him answer François’ 10 questions.

Greg Skeene - Wi-Fi Engineer

Location-Based Analytics

This episode was recorded at Cisco Live 2018 in the Podcast Domain. Our guest is Christian Gauer, a TME in Cisco focused on location-based analytics.

We’re new to location-based analytics so we wanted to know more about it. Especially with the increased amount of IoT devices coming on the network. Can we use that data to make business decisions?

What are some of the expectations for location-based analytics? We can expect to do way-finding, locating a device, using an app to locate yourself to draw line on the map of where to go.

Location is calculated by a Cisco CMX box. Data going into CMX needs to be accurate. This means design will be critical. APs should be mounted on the ceiling up to 20 feet high. Multi-trangulation is used in measuring distance-based on RSSI.

More accurate measurements is done with angle of arrival. Multi-trangulation needs more than 3 APs for higher accuracy. More than just triangulation. Why 3 APs minimum? Because of triangulation. With wireless location, a device needs to be inside context of APs. For location, start at the perimeter of the walls.

But why go into location-based analytics? Everyone wants to know whats going on. Top use cases – retail wants to know what’s going on in a shop and how much time customers are spending time in the shop and which section. An airport may want to know what’s going on with security, how much time people are spending there, or maybe there are too many people crowding at the gate.

Take a coffee chain with many locations into consideration. They offer free Wi-Fi. Device get connected and now the coffee chain can track who is connecting to their Wi-Fi network. But how many APs does a coffee shop need? Maybe need 1 or 2 APs for coverage. What kind of info can you get out of it? Is it important where someone sits, maybe not? It can be difficult differentiating someone sitting next to another.. or lining up. Presence provides detection of customer which means you can find out who is stopping by multiple shops. This is how you identify return visitors and measure dwell time. Other methods of using location-based analytics includes having an idea of how busy the store is for staff planning or how long it takes customers to get cup of coffee.

But a store needs to ask the question from the customer point of view, why should I connect to the Wi-Fi? There has to be an offer.

Listen to the episode for more details!

Links & Resources

CTS 131: 802.11 Authentication and Association

What frame exchanges are part of a device joining an SSID?

CWS & CWT Book Giveaway

We’re raffling off a two bundles of the CWS & CWT books from CWNP. Two winners will get a copy of each book. If you’re getting into Wi-Fi or would like to know the fundamentals so you can sell Wi-Fi then this is a good resource to use. All you have to do is fill out the form below.

Meet Dustin Johnson

Our feature wireless engineer for this episode is Dustin Johnson. We ran into him at Cisco Live by accident and he happens to be a listener of the show! Listen to the episode to hear him answer François’ 10 questions.

Dustin Johnson of Wal-Mart

802.11 Authentication and Association

How does the station (STA) and access point agree to this connection? We’re going to break down the steps and the frames that are part of a STA connecting to an access point.

We have one STA connecting to an open SSID. The summary of it all is as follows:

  • STA is unauthenticated and unassociated
  • STA becomes authenticated and unassociated
  • STA becomes authenticated and associated
  • STA clears security requirements such as 802.1X, if required

Summary of frame exchanges

Beacon/Probe

The STA begins the process by performing a passive or active scan. In passive mode, the STA is listening for beacons from an access point. The beacon frame contains the BSSID which is the MAC address of the radio sourcing from the access point.
The beacon frame is a type of management frame defined in 802.11-2016. It includes capability information and parameters.

A probe is sourced from the STA requesting to join a wireless network. This is a probe request management frame. The probe is responded by an access point using a probe response management frame.

Frame exchange in 802.11 authentication and association

Authentication

The probing/scanning phase is part of the unauthenticated and unassociated step. The STA has not authenticated with the access point and also is not associated with the access point. Think of authentication as plugging a computer into a port on a switch.

The STA must be authenticated to the access point before it is associated. It sounds backwards. These are the two states in this phase and it must be done in this order.

  • Unauthenticated or authenticated.
  • Unassociated or associated.

To begin the Authentication step, the STA sends an Authentication wireless management frame to the access point. The access point responds with an Acknowledgement frame.

The access point will acknowledge the Authentication frame from the STA and upon successful authentication, the access point will send an authentication frame to the STA with an Authentication Sequence with a State of 2, for success.

Access point sends an Authentication frame with a state of 2, for Successful.

Association

Once the STA is authenticated to the access point, the next step is to become Associated. The Association occurs after the Shared Key Authentication or Open System Authentication Algorithm. There cannot be a STA that is Associated but not Authenticated. If the STA fails Authentication, it does not move to Association.

After the the access point sends an Acknowledgement to the STA’s Authentication Response, the STA sends an Association Request.

The Association Request is Acknowledged by the access point which then sends an Association Response frame to the STA.

If the association is successful, the access point’s Association Response frame will contain a Status code: Successful.

The details within an Association Response include:

  • Capabilities Information such as
    • Supported Data Rates
    • HT Capabilities
    • HT Information such as the Primary Channel
    • WMM information
    • And more..

If the Status code is anything other than Successful, then the STA is deauthenticated.

Links And Resources

CTS 130: RF Characteristics

Get your basics of Wi-Fi starting with RF characteristics.

Before we get into RF characteristics, we want to introduce our series of interviews we did at Cisco Live 2018. We interviewed many wireless engineers to get to know them better. We ask ten questions, we get ten answers. So meet Jason Beshara. We introduce him starting at minute 7:06.

Jason Beshara at Cisco Live 2018

Jason Beshara at Cisco Live 2018

RF Characteristics

RF is Radio frequency. When talking about Wi-Fi we are referring to unlicensed radio frequency in the 2.4 GHz and 5 GHz spectrum. Wi-Fi is not the only radio frequency in the air. There are other frequencies such as microwave and AM/FM radio.

A carrier signal is used to take AC signal from the radio to turn it into a waveform. Information is transmitted from the antenna on the carrier signal as an electromagnetic wave.

Modulation is done to modify the signal to create the carrier signal which will carry the 1s and 0s.

When defining a wave, we talk about its wavelength. It is the distance between two identical points in a wave. Higher frequencies have a shorter wavelength thus they get attenuated faster. Lower frequencies have longer wavelengths.

A wavelength

Wavelength with peaks and troughs

Another characteristic of an RF wave is its amplitude. This is the power of the wave or signal strength from the transmitting device. As signal is propagated through the air it is received at a lower amplitude. Higher amplitude increases the chance of the receiver successfully demodulating the signal.

Frequency is another characteristic. This is the interval in which the wave repeats or oscillates. A 2.4 GHz signal repeats 2.4 Billion cycles per minute. Higher frequencies have shorter wavelengths.

Then we have phase. Phase compares two RF waves. If a device receives two copies of an RF wave, the phase can determine whether it is positive or negative. To make multiple RF waves positive, they would need to be in-phase. This would strengthen the wave or increase the amplitude thus increasing the ability to demodulate signals. If received signals are out-of-phase, the signals may cancel each other out if 180 degrees out of phase.

How can RF be affected in the real world? We talk about some of the ways below and in the episode:

Reflection

When a signal bounces off an object such as a mirror or metal. It’s like aiming a flashlight onto a mirror and the signal bounces in a different direction.

Absorption

This occurs when RF goes through material such as a wall. Absorption will weaken a signal (attenuate). Material such as dry wall, concrete, doors, windows, etc. Each material has different attenuation values. Shine a flashlight through a white sheet and some signal is absorbed by the material.

Refraction

When signal goes through a different medium, such as water, the signal is bent. Take a glass of water, as an example, and notice how light shining through one side is bent leaving the other side.

Scatter

Signal that hits an uneven surface and reflected in multiple directions is scatter. Think of a disco ball or chain link fence. As signal hits these surfaces it is reflected everywhere.

Diffraction

Diffraction occurs when a signal goes around an object. Like a rock in the middle of a flowing river. Water flows along the sides of the rock. Directly behind the rock there is less of a current from the stream. With Wi-Fi, signal may not go through a concrete pillar but it will go around it. But a device directly behind that pillar will be in an RF dead zone or RF shadow.

Attenuation

Earlier we talked about absorption. Attenuation is when there is a decrease in amplitude and the signal is weakened or there is a loss of signal. This can commonly happen through absorption.

Multipath

Multipath is a result of scatter and reflection. A device can receive multiple copies of the same signal through multipath.

Links and Resources

CTS 129: 5G Technology

Recorded at Cisco Live 2018 in Orlando, Florida. We speak to Mike Geller and Pramod Nair about 5G technology and what Wi-Fi professionals would know about.

5G Technology

Rowell Dionicio, François Vergès, Mike Geller, and Pramod Nair talking about 5G

We’ve been hearing a lot about 5G lately. But do many of you what is involved with 5G? We just know it’s the next number up from 4G 😉

We recorded an episode with Mike Geller and Pramod Nair, Cisco employees, at the Podcast Domain in Cisco Live Orlando, Florida. There’s some background noise from the attendees at Cisco Live but you’ll still be able to hear the conversation.

As Wi-Fi professionals, what should we know about 5G? What is it all about? Hopefully, Mike and Pramod can shed some light on this topic for us.

First thing to know, is 5G caters to a set of use cases. Pramod points out this is the first time we’ve seen something driven by use cases. Some of those use cases for 5G are low latency for IoT and fixed wireless access. There’s the vehicle to everything use case. It can include Wi-Fi transmission but doesn’t define what RF interface to use, regulated or not.

What we do know, spectrum is always going to be a scarce, finite, resource. There is a possibility to use Wi-Fi and LTE together. Possibly use Wi-Fi on specific IoT use cases so we can better use spectrum more efficiently.

More importantly, we will not see 5G replace Wi-Fi. Mike Geller and Pramod Nair do not consider them as competing technologies.

Wi-Fi has been there yesterday, Wi-Fi is there today, Wi-Fi will be there tomorrow. – Pramod Nair

If you listen around the 10:50 minute mark, Pramod makes a funny statement. 

The differentiator in 5G is the network has the capability to tell the device which slice of network resources it should follow. There can be a radio interface to cover your phone, your friends phone, and another phone. Each phone can have a different profile because of data packages. You can put any of those phones on a different slice all together. Here, it just becomes more flexible. The network is becoming more complex but the use case is becoming easier.

Listen to the episode to hear the full conversation.

Links and Resources