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Enhancing HDX: Improved Mitigation of Wi-Fi Interference through Wi-Fi-Triggered Event-Driven Radio Resource Management (ED-RRM)

Cisco Systems is announcing a new set of features that enhance its HDX (High Density Experience) suite. This blog is the fourth in a series that explains the new features that comprise the enhancements to HDX.

The first three blogs in the Enhancing HDX series are here and here and here.

The rapid and massive adoption of Wi-Fi into handheld devices has created new challenges for managing a wireless network.

As a consequence, the traditional view of a rogue Access Point has to change. The advent of mobile APs and Wi-Fi Direct (client to client networking without requiring infrastructure) means that rogue devices don’t need to be “connected” to the infrastructure in order to create a potential for nuisance.

Effectively these capabilities mean that “Bring Your Own Device” (BYOD) may also mean “Bring Your Own AP” or “Bring Your Own Network” and therefore “Bring Your Own Interferer”. Thus the threat from a rogue becomes less about security and more about consuming excessive air time (a so-called “spectrum hog”) thus degrading performance in the WLAN. This can be especially troublesome in high density pubic venues but can also be problematic in enterprises.

So in addition to Cisco CleanAir (which mitigates and reports on non Wi-Fi interference) and RRM (which primarily prevents self induced neighboring AP interference via DCA and TPC for the entire WLAN) Cisco is effectively merging aspects of both of these solutions in order to provide improved mitigation of Wi-Fi that is not affiliated with the production WLAN.

Enhancing HDX 1

Accounting for rogue Wi-Fi interference is accomplished by configuring a trigger threshold for ED-RRM. This is effectively a severity indicator so that the affected access point that has ED-RRM is additionally triggered by Wi-Fi interference.

Enhancing HDX2

Since rogue severity is now added to the ED-RRM metrics, this provides the capability of a faster channel change than the typical DCA cycle. In other words, if a rogue is interfering with airspace, then instead of waiting until the next DCA cycle to elapse, change the channel as quickly as possible. This is the same behavior as for mitigating non-Wi-Fi interferers with Cisco CleanAir technology.

Since Wi-Fi interference is becoming more prevalent, rogue APs that are serving traffic to clients (e.g., mobile APs) or client devices creating networks in real time means that air quality will be affected. Wi-Fi needs to be prevented from becoming a problem by reacting to the presence of client devices that are legitimately acting as independent, unaffiliated networks.

 

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Enhancing HDX: Optimized Roaming extended with 11v BSS Transition Management

Cisco Systems is announcing a new set of features that enhance its HDX (High Density Experience) suite. This blog is the third in a series that explains the new features that comprise the enhancements to HDX.

The first blog in the Enhancing HDX series is here. The second blog in the Enhancing HDX series is here.

What is 802.11v? What is BSS Transition Management? Why are these Important?

In this blog, two different series are intersecting: Enhancing HDX and the series looking at the lesser known but undeservedly underappreciated amendments to 802.11 and the features/benefits they provide.

Previous blogs briefly explained the basics of 802.11k “WLAN Radio Measurements” and specifically zoomed in on the Neighbor Request/Report and also explained the basics of 802.11r “Fast BSS Transition”

This blog will briefly explain the basics of 802.11v “Wireless Network Management” and will also explain how 802.11k Neighbor Request/Report and 802.11r “Fast BSS Transition” can provide a “better together” solution with 802.11v. It also explains where it fits in with High Density Experience (HDX).

Wireless Network Management (802.11v)

Wireless network management (WNM) enables devices comprising the WLAN to exchange information with the goal of improving the quality of experience when using the WLAN. Network administrators benefit from using WNM by having additional ability to fine tune the WLAN in order to provide improved reliability of services to their end users and the end users benefit in turn from using a WLAN that has been designed to provide more than mere connectivity.

Client devices and infrastructure may both use WNM to exchange operational information so that both clients and infrastructure have additional awareness of the WLAN conditions. That awareness can help provide a firm foundation for self-correcting events and actions to be implemented. In other words, WNM isn’t about being a “control freak”; it’s about raising the bar in the Wi-Fi ecosystem so as to create better Wi-Fi networks.

But not only does WNM provide information on the state of network conditions, it also provides a means to exchange location information, supports efficient delivery of multicast (group addressed) frames, and enables a power savings mode in which a client can sleep for longer periods of time without receiving frames or being disassociated from the AP.

Given this, it can be easily appreciated why WNM has often been described as a “kitchen sink” of features. This blog won’t take the time to go through each and every feature introduced in the 802.11v amendment. But in order to emphasize the potential richness of the feature set, the following is an alphabetized list:

HDX1

The remainder of this blog is going to focus on BSS Transition Management. Future blogs will cover other aspects of 802.11v.

BSS Transition Management Read More »

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Enhancing HDX: Introducing FlexDFS – Not All DFS Solutions Are Created Equally

Cisco Systems is announcing a new set of features that enhance its HDX (High Density Experience) suite. This blog is the second in a series that explains the new features that comprise the enhancements to HDX.

5 GHz is a great place to operate a WLAN. There is ample spectrum, and it’s far less crowded and noisy than 2.4 GHz.

However, the majority of 5 GHz spectrum is shared with radar (for both weather and military systems). Therefore, Wi-Fi Access Points not only need to detect radar in order to avoid interference but also need to avoid being an interferer to these systems.

This procedure is commonly referred to as DFS or Dynamic Frequency Selection.

For DFS operation, if radar is detected on a channel then the AP must abandon that channel from further operation for some minimum amount of time. Furthermore, the AP must ensure that any new channel it selects for operation is free from radar (and that detection also requires a minimum amount of time).

Finally, accurate detection of radar (i.e., avoiding false positives) also requires a lot of skill. Compounding the issue are many devices that emit “radar like” transmissions (including Wi-Fi clients and APs doing proprietary over the air detection and calibration).

As a result, many equipment vendors simply take the easy way out and avoid use of the channels requiring DFS.

Cisco believes it has the best DFS solution in the wireless industry and that it only gets better with  a new feature we’re calling Flexible Dynamic Frequency Selection (or for short, FlexDFS). Read More »

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Enhancing HDX: Introducing Dynamic Bandwidth Selection – Automatically Choosing the “Best” Channel Width

Cisco Systems is announcing a new set of features that enhance its HDX (High Density Experience) suite. This blog is the first in a series that explains the new features that comprise the enhancements to HDX.

Every advancement in Wi-Fi technology comes with corresponding complexities and tradeoffs.  You just don’t get something for nothing.

For example, much of the speed improvements in the evolution from 11b to 11g/a to 11n to 11ac are achieved by simply doubling the RF channel width. Increasing channel width from 20 MHz to 40 MHz effectively enables doubling “over the air” speed. Increasing channel width from 40 MHz to 80 MHz doubles that speed again.

Of course, wider channels are more susceptible to interference (since a wider channel can “hear” more). Furthermore, with wider channels, the number of available so called “non-overlapping” channels decreases making mutual interference an increasing problem. Being able to send data over the air faster is very important, but if the devices in your WLAN are waiting more often to send data because the wider channel is more likely to be busy, then disappointment and unrealized expectations will occur. Keep in mind that because “air is shared” for Wi-Fi that it uses a “listen before talk” protocol.

Also, in a real world WLAN, it is highly unlikely to have homogeneous device types. The client mix will include legacy devices that simply can’t operate at 80 MHz (or 40 MHz). This means that spectrum could be wasted if the network is configured for a greater channel width than most of its devices can handle. This has far more consequences at 5 GHz than at 2.4 GHz since 40 MHz channels are unlikely to be usable at 2.4 GHz and 80 MHz channels cannot be used at 2.4 GHz.

Interestingly, 802.11ac does include a feature called RTS/CTS with bandwidth indication that is intended to address dynamic channel width (read more about this in 802.11ac: The Fifth Generation of Wi-Fi” section 2.3.4). The challenge is that this feature is not often used and cannot be used by either 11a or 11n clients.

Last, but far from least, no two wireless networks are the same – every wireless network is different. Even parts of the same wireless network will be different. Thus, there really is no “one size fits all” static configuration that helps offer optimization. The Wi-Fi network needs to adapt as conditions change. Read More »

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What is 802.11r? Why is this Important?

In this short series of blogs, we’re spending some time looking at the lesser known but undeservedly underappreciated amendments to 802.11 and the features/benefits they provide.

The first blog explained the basics of 802.11k “WLAN Radio Measurements” and specifically zoomed in on the Neighbor Request/Report.

This blog will focus on the 802.11r amendment.

Fast BSS Transition (802.11r)

Fast BSS Transition (often abbreviated to Fast Transition or FT) describes mechanisms by which a mobile device can reestablish existing security and/or QoS parameters prior to reassociating to a new AP. These mechanisms are referred to as “fast” because they seek to significantly reduce the length of time that connectivity is interrupted between a mobile device and Wi-Fi infrastructure when that mobile device is connecting to a new AP. Please note that the process of disconnecting from one AP and connecting to another AP is formally designated as a “BSS transition”. Therefore, the protocols established by FT apply to mobile device transitions between APs only within the same mobility domain and within the same ESS (ESS transition is out of scope for FT). Since both reassociation and reauthentication are time critical processes, removing time consuming message exchanges between the mobile device and the infrastructure help reduce interruption to high value services (e.g., voice and/or video) when transitioning from one AP to another especially in a strongly secure WLAN (i.e, one using 802.1x and EAP methods for authentication).

Because Fast BSS Transition reestablishes existing parameters, the protocols require that information be exchanged during the initial association (or at a subsequent reassociation) between the mobile device (formally referred to as the FT Originator (FTO)) and an AP. The initial exchange is referred to as the FT initial mobility domain association. Subsequent reassociations to APs within the same mobility domain are expected to utilize the FT protocols.

Two basic FT protocols are described:

  1. FT Protocol. This protocol is performed when a mobile devices transitions from one AP to another AP but does not require a resource request prior to its transition. The AP selected by the mobile device for reassociation is referred to as the “target AP”.
  2. FT Resource Request Protocol. This protocol is performed when a mobile device requires a resource request prior to its transition.

For a mobile device to transition from the AP it is currently associated with to a target AP, the FT protocol message exchanges are performed using one of two methods:

  1. Over-the-Air. The mobile device communicates directly with the target AP using IEEE 802.11 authentication with the FT authentication algorithm.
  2. Over-the-DS. The mobile device communicates with the target AP via the current AP. Communications between the mobile device and the target AP are encapsulated within FT Action frames between the mobile device and the current AP. Communications between the current AP and the target AP, occurs via a different encapsulation method. The current AP converts between the two encapsulation methods.

802.11r image 1

Over the Air message exchange (excerpted from IEEE 802.11-2012)

802.11r image 2

Over the DS message exchange (excerpted from IEEE 802.11-2012) Read More »

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