Coming off the Cisco Champion Radio podcast, François and Rowell share their RRM experience.
Our Cisco RRM Experience
We use Cisco RRM on a daily basis and in most of the environments we configure and manage. It’s come a long way since it’s introduction but we’re both still learning so much about Cisco RRM.
For a large environment, RRM is a useful tool. But when changes are done on the WLAN, RRM needs to be reset and settled.
In this episode, we talk about our experience using RRM. What does it mean to design with RRM in mind? How does one use RRM with high density, capacity, coverage, etc while keeping ensuring it meets requirements.
We touch upon using design tools such as Ekahau Site Survey and how you use those design tools with RRM. Can it be done?
And what do we think about those who don’t think RRM works at all? We touch on that just a little.
Take a listen to the episode and share your experience in the comments below.
François and I were fortunate to be able to host Cisco Champion Radio this week. We tackled the topic of Cisco Radio Resource Management (RRM) with subject matter expert, Jim Florwick.
Jim is a Technical Marketing Engineer with deep knowledge of how Cisco RRM works.
I started off the conversation by asking Jim what the most common misconceptions are of RRM. He provides a great response because many people seem to leave RRM at its defaults or believe RRM would fix all their RF problems.
Jim provides insight into how the algorithms work and how you should consider them into your design or existing WLAN infrastructure. The important tip he provided was to initiate a DCA restart when major changes have been applied to the WLAN. These changes can be new APs, channel changes, a new controller, you name it.
François asked an important question, how do you perform your validation surveys with RRM in mind? Jim responded with freezing RRM to prevent any changes from occurring while you’re conducting your validation survey. You don’t want to see the same AP shown with two different channels or have transmit power changing while you’re doing your survey.
We then go into the addition of FRA and the complexity it adds to RRM and other topics as well. Give the episode a listen on SoundCloud!
Fred Niehaus and Wes Purvis, of Cisco, discuss how the network sensor brings an impact with Wi-Fi assurance.
The Network Sensor
This episode was all brought together because of a recent announcement of Cisco’s dedicated Wi-Fi network sensor. A smaller AP-looking device, similar to the Cisco 1815, that can be wall-mounted or placed close to the users. It’s purpose is to validate Wi-Fi connectivity.
Named the Cisco Aironet Sensor, there are three components:
Wireless performance analytics
Real-time client troubleshooting
Proactive Health Assessment
Wes Purvis talks about the requirements of running the dedicated sensor:
Cisco WLC with 8.5 MR2
Cisco DNA Center
Cisco Aironet Sensor Tests
François and Rowell ask why even build a sensor with other companies in the market also developing their own kind of sensors. Primarily it was to give more visibility into the network and to do prescribed testing.
The Cisco Aironet Sensor will associate directly with a Cisco AP. Various health checks can be performed by acting like a client device. The results of those tests bypass the Cisco WLC and get reported directly to Cisco DNA Center.
There are three modes to the sensor:
Wave 2 AP as a sensor
Radio as a sensor
Results of the tests ran by the network sensor
Those last two modes are interesting. A Wave 2 AP can stop serving clients and become a sensor itself to run any diagnostic tests. The third option is available to APs with an XOR radio. One of the radios goes out of service to clients and acts as a client itself, connecting to other APs.
In the episode we did speak about turning an AP into a sensor and the cautions there. Because APs are not near the clients, the results may not reflect the experience of a real client.
Currently, Cisco supports a number of different tests on the sensor. There are about 10-15 available with future expansion into custom tests. Some of those tests include:
Connect to an IP address
Download a webpage
Let us know what you think below in the comments after you listen to the episode with Wes Purvis and Fred Niehaus.
This Week In Wireless
New CWNE this week – Oguzhan Eren from Turkey became CWNE #266
CWNP Wi-Fi Trek Registration – The registration for this years CWNP Wi-Fi Trek conference begins on March 12th. Registration Link
T-Mobile Annouces Plans to Deploy 5G in 30 U.S. Cities this year. T-Mobile is already installing 5G equipment as it continues to build its LTE network in the US. The company should be able to deploy a comprehensive 5G layer in time for the debut of 5G consumer devices next year. The service will be used over the 600 MHz spectrum along with spectrum in the 28GHz and 39GHz bands. First cities to be served: New York, Los Angeles, Dallas and Las Vegas. Read more here.
Following a Twitter conversation which happened last weekend driven by Jeremy Ward on Private LTE networks or LTE network in general. Jeremy recommended the lteuniversity.com website to start learning about LTE.
The earliest Cisco WLC version where Cisco CleanAir was released dates back to the 7.0 days. Sometime around the year 2010. Cisco CleanAir is always on within an AP, granted if it is Enabled in the WLC. There is a Spectrum Analysis Engine (SaGE) chip built into the AP. This is important to know because it doesn’t prevent the AP from serving clients. SaGE works alongside the Wi-Fi chip. There is no affect to client throughput or traffic.
To enhance Cisco RRM’s features, CleanAir plays a critical role in allowing RRM to change channels if persistent interference is detected. CleanAir will field the appropriate algorithms to help the WLC make changes to improve an environment.
Cisco CleanAir produces two important elements:
Interference Device Report
Air Quality Index
The Interference Device Report (IDR) provides information on detected interference. It will provide a class type, what band the interference was detected on and on what channel(s), the severity of the interference, it’s duty cycle, and the interference signature.
The Air Quality Index (AQI) provides a quality score, from 0 – 100%, with 100% being good. The index will display total channel power, total channel duty cycle, the power of the interferer and total interference duty cycle.
A benefit of using Cisco CleanAir is having the ability to troubleshoot the shared spectrum remotely and without any additional hardware. A CleanAir supported access point can be utilized for this purpose. Some things to keep in mind when using your CleanAir access point for troubleshooting interference:
There are three modes:
Local – The AP will continue to serve clients on its operating channel. But any spectrum monitoring is performed on that channel only.
Monitor – The AP doesn’t server any clients but provides full time scanning.
Spectrum Expert Connect – This is a dedicated spectrum sensor and doesn’t serve any clients.
In times when the best response is to use technical support hands to troubleshoot the issue, having a method of automatically mitigating an interference issue can be highly beneficial. It can cut time to resolution down and react faster than a support team that is reactionary.
What we’d like to see from CleanAir is the ability to tell an administrator whether any action needs to be performed. While interference and air quality is determined on any given channel, does it even matter? Are any users impacted negatively? A smarter system would be able to detect interference and provide exactly which users are having issues directly related to this interferer and what kind of impact that is. And a step further would be to automatically adjust the system to fix the problem.
We’ve included some images of Cisco CleanAir in action from within Spectrum Expert and Metageek Chanalyzer.
DCA, or Dynamic Channel Assignment, is a core component of Cisco Radio Resource Management (RRM). It runs a critical algorithm which dynamically changes an access points (AP) client serving channel based on multiple parameters, collectively called a Cost Metric. To really get an understanding of Cisco RRM, start with our previous episode on Cisco NDP.
DCA is configured under 802.11a/n/ac (5 GHz) and 802.11b/g/n (2.4 GHz)
Channel Assignment Method
The first thing you will notice is the Channel Assignment Method of Automatic, Freeze, or Off.
Automatic will run the DCA algorithm at the define Interval which is every 10 minutes by default. The anchor point is used to set the time of day the DCA algorithm would start.
For less frequent channel changes, increase the interval.
Keep in mind that clients will be disconnected briefly for a channel change.
Freeze does not run the DCA algorithm unless triggered.
Off disables the use of RRM and its auto-rf capabilities.
Avoid Foreign AP interference
Enabling this option allows RRM to take surrounding neighboring APs that are not part of your network into consideration.
RRM will create a channel plan to help mitigate co-channel interference.
Avoid Cisco AP Load
This option allows RRM to consider the traffic load on an access point to help build a better channel plan.
I don’t believe in enabling this feature because it can be difficult to make a client device associate with a specific AP.
Avoiding non-802.11a|b noise
This RRM option takes interference on the channel into consideration for the channel plan.
The category of interference is anything coming from a non-AP.
Persistent Device Avoidance
Sometimes there is non-Wi-Fi device interference affecting your wireless network. DCA can help mitigate the issue if Avoid Persistent Non-WiFi Interference option is enabled.
RRM will receive information from CleanAir and if the interference is creating a negative impact, RRM can issue a channel change to avoid it.
Viewing persistent devices can be done by viewing the details of an AP from the web interface. At the bottom of the page are all the persistent devices being tracked including the class type, on what channel the interference was heard, what the duty cycle is, RSSI, and when it was last seen.
DCA Channel Sensitivity
DCA has three different modes it could be in:
Scheduled – DCA algorithm runs at a selected time. Usually to minimize changes to off peak hours.
Steady State – DCA algorithm running at a specified interval.
Startup Mode – Used when making changes to the wireless network architecture. It restarts the DCA algorithm and runs for 100 minutes at high sensitivity.
By default, DCA has a medium channel sensitivity at 15 dB for 5 GHz and 10 dB for 2.4 GHz. This is the DCA Sensitivity Threshold.
By changing the channel sensitivity to high, then a cost metric of 5 dB better will recommend a channel change.
DCA Channel List
To have DCA dynamically select a channel, it must be in the Channel List. You can select specific channels for DCA to select from or select them all, including the UNII-2 channels.
Dynamic Bandwidth Selection
RRM has a flexible way to assign bandwidth to APs by analyzing the RF and selecting the best channel width.
By default, DCA uses 20 MHz channels. You can configure Cisco RRM DCA all the way up to 160 MHz channels or select Best to have RRM pick for you.
If an AP doesn’t support 40/80/160 MHz channels it will not be configured for it.
To see DCA dynamically select channels, head over to the CLI on the controller and enter the debug command:
debug airewave-director channel enable
*RRM-CLNT-5_0: Aug 27 12:04:48.270: 58:bc:27:33:33:33 Slot 1: Channel set request on 58:bc:27:33:33:33(1) to (100, 104, 0, 0) 40 MHz Before -62, After -72 Second best: ch 157 wd 40 mt -86 RRF:enabled(0) metric(199)
*RRM-CLNT-5_0: Aug 27 12:04:48.270: [spamGetMeshBhRRMStatus] 0
*RRM-CLNT-5_0: Aug 27 12:04:48.270: 58:bc:27:33:33:33 new channel width label set from 3 to 4
*RRM-CLNT-5_0: Aug 27 12:04:48.270: 58:bc:27:33:33:33 slot 1 Set new channel 100 width label 4
*RRM-CLNT-5_0: Aug 27 12:04:48.270: 58:bc:27:33:33:33 sent channel to spam and call trap(0)
*RRM-CLNT-5_0: Aug 27 12:04:48.270: 58:bc:27:33:33:33 Airewave Director: Final Channel Assignment (100,104,0,0) configured on AP 58:bc:27:33:33:33(1)
*RRM-CLNT-5_0: Aug 27 12:04:48.270: 58:bc:27:33:33:33 Airewave Director: set channel on cell 58:bc:27:33:33:33(1) to 100 from 100 to reduce co-channel interference from (-128,-128,-62) to (-128,-128,-72) reason 1
In the output above, Cisco RRM DCA made a request to change an AP to a 40 MHz channel width using primary channel 100 and secondary 104.
At the very end, RRM sets the channel to 100 with the reason – to reduce co-channel interference.
From command line, it is possible to view when the last channel assignment was set using the following show command:
show ap auto-rf 802.11a <ap-name>
Channel Assignment Information
Current Channel Average Energy............... -71 dBm
Previous Channel Average Energy.............. -71 dBm
Channel Change Count......................... 541
Last Channel Change Time..................... Sat Aug 27 12:14:59 2016
Recommended Best Channel..................... 116
802.11a – shows the 5 GHz radio 802.11b – shows the 2.4 GHz radio <ap-name> – replace with the name of your AP
The output was truncated just to display the channel assignment information. You can see the current and previous channel average energy, how many times the channel has changed, when it was last changed, and which is the best recommended channel.
Event Driven RRM
If you need the wireless network to react quickly and automatically to bad interference, ED-RRM is an option to enable.
An example could be a device using 100% duty cycle causing all nearby APs and clients to hold off communicating on the wireless medium. ED-RRM would allow an AP to make the channel change sooner than when the DCA interval kicks in.
To configure ED-RRM:
1. Click on Wireless
2. Click on 802.11a/n/ac or 802.11b/g/n
3. Click on DCA
4. At the bottom of the page, enable EDRRM
5. Set the sensitivity threshold to Low (my recommendation is not go above Medium)
The sensitivity threshold defines the air quality (AQ) at the following:
Low sensitivity – AQ at 35%
Medium sensitivity – AQ at 50%
High sensitivity – AQ at 60%
An air quality of 100% is good, very bad is 0%
The Rogue Duty-Cycle option will allow you to set the percentage of duty cycle and rogue duty cycle occurs before triggering EDRRM.
To learn more details about Cisco’s RRM – DCA be sure to check out the white paper from Cisco.