Campus Best Practice (GN3/NA3/T4) WLAN Network Planning

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Campus Best Practice (GN3/NA3/T4)

WLAN Network Planning

Anders Nilsson, SUNET

Wireless Training Workshop Belgrad, 12 September 2011

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WLAN Network Planning

Agenda

• Wi-Fi standards (a/b/g/n …….) • RF Basics (know your layer 1)

• Preparing for a site survey

• Cell planning (size matters)

• Practical issues in placing accesspoints

• Planning and verification tools (demo time)

• Practical experience WCS demo from Umeå (if Murphy allows)

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Note!!

In theory 802.11n will might reach 600Mbps with 4 spacial streams running on 5GHz but 450Mbps is

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Timeline of 802.11 standards.

802.11n is not the end of the development.

The standardization of 802.11n was a record long 6 year journey.

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New installed accesspoints should be 802.11n based and operating on both 2.4 and 5 GHz band. Higher capacity means more room (Airtime) for clients and more throughput.

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2.4GHz is limited to only 3 non-overlapping channels (1-6-11) and is constantly filling up with other non-Wi-Fi devices competing for the spectrum. The future is 5GHz where you have a least 20

non-overlapping channels (varies between countries). Also note that only 5GHz will get you 300Mbps (channel bonding) with 802.11n.

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Always aim for the best fuel at the gas station. 

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The dynamic nature of spectrum

• You are breathing the physical layer • RF reflects off things

• RF is absorbed by things (walls, windows, furniture)

• It’s a shared medium (as such, not all RF is always yours) • Not all RF is 802.11 traffic (especially true with 2.4GHz)

• In order to see what’s really going on you might need more than a WiFi card.

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About Decibels

Used to measure large dynamic ranges • It is dimensionless

• A Decibel is a ratio

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WLAN Network Planning

Please note that these 802.11b

threshold levels are very depending on your devices

antenna

performance and the sensitivity of the chipset (varies).

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And yes, other signals that the wifi chipset can’t recognize (Bluetooth, Dect phones, Microwave Owens ) will be considered noise.

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Cell size. Typical SNR versus speed values for 2.4GHz.

Note how much more efficient 802.11g with ODFM is, you get 12Mbps versus 6Mbps with the same SNR

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Yes 5GHz loses more but normally also have a much lower noise floor due to less co-channel interference

Please note:

Distances in feet Attenuation in dB

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An 802.11n accesspoint improves reception on older abg-client.

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Interference mitigation

Finding these evil polluters will need something better than an

ordinary WiFi card. A higher resolution RF-spectrum analyzer device like Metageeks WiSpy (see demo later), Cisco’s Spectrum Expert or similar products are the right tools for this kind of job.

Note that Ciscos latest APs with so called Clean Air capability include an spectrum analyzer chip (great but at an extra cost)

Even though the source of the interference is located you might end up having to keep the interferer. Removing Microwave Owens from the kitchen may be a problem. 

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WLAN NETWORK PLANNING

What type of WLAN are you building?

Three basic types WLAN design focuses:

• Coverage (as large area as possible) Outside coverage?

• Capacity (high density of user over a given area)

• Location (the possibility to locate clients)

Because the cell size dictates the capacity there’s a tradeoff between high Coverage and high Capacity. Location usually leads to more Aps required.

Can we get rid of older legacy protocols?

Disabling 802.11b will effectively almost double the capacity on 2.4GHz. Disable at least 1 & 2 Mbps and consider 5,5Mbps if 802.11b is left.

What type of applications should run?

Wireless Voice over IP (VoWLAN) demands certain attention (not covered in this presentation)

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What type of clients do you have?

Are you sitting with older client not supporting 802.11n. Make sure all newer clients support 802.11n on 5GHz also. Can we phase out old 802.11b ones? Also take into account that different clients have different RF-performace and hence you must find the “Vorst” client type and use that one as reference.

How many SSIDs do we need?

There should never be more than 5 SSIDs per AP even though the AP itself may support many more. 802.11u will solve this limitation in the future.

What are the roaming requirements?

Are we just building a single hotspot or do we need continuous coverage

Do you have a monopoly on setting up APs?

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WLAN Network Planning

Perform an onsite site pre-survey

Try to get hold of the drawings of the building. But after that it’s very important to visit the location in person to understand if the drawing is still current or if walls have moved or reinforced or something similar. Really ambitious people classify walls and the manually input that info to their Wlan planning software (very time consuming). Anyway to

know where thick walls and elevator shafts are and maybe also look for modern high insulating windows (can reduce the signal more than 12dB) is very important.

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Spot check design

Rather than setting up all the APs at once simply select an area of you building and set up 3-4 APs according to your design and then verify. If your calculations seems to be right you can continue. Another method is to bring up the APs one by one (time consuming) but my experience is that you need to have 3-4 APs running and than after the RRM has done it’s magic se what the result became.

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Setting up APs

Make sure you read the instructions so that the accesspoint can work with full performance. To put it short the AP needs “breathing space” and to be mounted in the way the company manufacturing it intend.

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The AP1130 was designed for the office environment. Easy mount on a 3m ceiling and propagate the signal down and wide.

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Verify coverage

Here there are many schools on how to proceed

I personally prefer to use the Aircheck from Fluke (2000 euro) A free alternative is to combine inSSIDer and iperf to both test the channel allocation and throughput.

An interesting alternative is Wi-Fi inspector from Xirrus

http://www.xirrus.com/library/wifitools.php but this one is maybe better for home users.

Don’t forget to read through the document titled .

gn3-na3-t4-wlan-network-planning which can be found at

http://www.terena.org/activities/campus-bp/pdf/gn3-na3-t4-wlan-network-planning.pdf

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Semi professional site survey on a shoestring budget?

Of all the soft ware I found on the Internet I believe the free version of Wavedeploy from Veriwave . www.wavedeploy.com

Ofcourse this product does not have all the bells and whistles as it’s full blown commersial versions but if you want a product where you can put your laptop on a trolley or just carry it around and marking on your map and end up with a god coverage map. I’ve not tested it yet myself but heard good reviews from colleagues in the

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If you want really good capacity in your cubicle

landscape you may have to install one AP every 9th_meter

but typically my experience is 16-20 meters depending on walls etc.

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Typical settings on Cisco controller with 802.11b disabled. This will decrease the cell size and increase the performance.

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My own view and recommendation on WLAN

• Stop using 802.11b clients and disable it on you WLAN • All new 802.11n clients should support 5GHz

• No more than 15 active associated clients per AP

• If possible a 20% overlap of the cells is something to aim for (for good roaming)

• You should never have less than -65dBm signal strength in your coverage zone

• Try to get RF-spectrum analysis tools for better understanding of what’s going on in your environment.

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