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

Transcription

1 Campus Best Practice (GN3/NA3/T4) WLAN Network Planning Anders Nilsson, SUNET Wireless Training Workshop Belgrad, 12 September 2011

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3 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) Q&A open discussion

4 Yes,Wi-Fi is datacommuncation over radio.

5 Note!! In theory n will might reach 600Mbps with 4 spacial streams running on 5GHz but 450Mbps is the limit right now.

6 Timeline of standards n is not the end of the development. The standardization of n was a record long 6 year journey.

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

8 Comparing 2.4 and 5GHz

9 802.11n? Yes, but what flavor? n? Yes but only on 2.4GHz

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11 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 nonoverlapping channels (varies between countries). Also note that only 5GHz will get you 300Mbps (channel bonding) with n.

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

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14 RF Basics (know your layer 1)

15 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 traffic (especially true with 2.4GHz) In order to see what s really going on you might need more than a WiFi card. Things don t stay the same, the only constant in the RF spectrum is change.

16 About Decibels Used to measure large dynamic ranges It is dimensionless A Decibel is a ratio Decibel is 1/10 of a Bel, but Bel is never used

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21 Please note that these b threshold levels are very depending on your devices antenna performance and the sensitivity of the chipset (varies).

22 And yes, other signals that the wifi chipset can t recognize (Bluetooth, Dect phones, Microwave Owens ) will be considered noise.

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24 Cell size. Typical SNR versus speed values for 2.4GHz. Note how much more efficient g with ODFM is, you get 12Mbps versus 6Mbps with the same SNR

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26 Please note: Distances in feet Attenuation in db Yes 5GHz loses more but normally also have a much lower noise floor due to less co-channel interference

27 Basic antenna types

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29 Interference (problems and why MIMO might be your savior)

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

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35 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. Depending on the type of interference you will end up with one or more channels ending up unusable.

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37 Preparing for a site survey

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40 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 b will effectively almost double the capacity on 2.4GHz. Disable at least 1 & 2 Mbps and consider 5,5Mbps if b is left. WLAN NETWORK PLANNING What type of applications should run? Wireless Voice over IP (VoWLAN) demands certain attention (not covered in this presentation)

41 What type of clients do you have? Are you sitting with older client not supporting n. Make sure all newer clients support n on 5GHz also. Can we phase out old b 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 u 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 WLAN NETWORK PLANNING Do you have a monopoly on setting up APs? Finding yourself being the sole master is rare but if possible this definitly is an advantage. Investigate if you can divide up between you and others.

42 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.

43 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.

44 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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46 The AP1130 was designed for the office environment. Easy mount on a 3m ceiling and propagate the signal down and wide.

47 Even though MIMO based n APs are bit more forgiving try to avoid these type of installations a much as possible.

48 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 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

49 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. 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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52 Per-User Application Throughput examples

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55 If you want really good capacity in your cubicle landscape you may have to install one AP every 9 th meter but typically my experience is meters depending on walls etc.

56 Large highly populated auditoriums need a different approach.

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

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62 My own view and recommendation on WLAN Stop using b clients and disable it on you WLAN All new n 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.

63 Yes!!! We made it.

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65 Further reading links : Discovering_WLAN_802.11n_MIMO.pdf Free access after registration, great mobile network presentations. If you only have time for one link I highly recommend this one.

66 Bonus slides

67 Viewing neighbor APs frequency and signal strength on WLC

68 RF-Interferers show up on WLC with ver 7 software and Clean Air APs

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71 Bad channel planning lead to co-channel interference Actual measurements from my hotel yesterday

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