November 6, 2013 1 Comment
You are likely reading this post at the recommendation of someone. You have likely asked something along the lines of ‘Will you do an 802.11ac site survey for me?”. This is an easy mistake to make, and I hope that this clarifies a few things for you. First and most importantly, any site survey should always start with the customer requirements, then you position the technology to fit those requirements. If you ask me for an 802.11ac survey, this means that you want a deployment that supports 802.11ac modulation. Modulation occurs at most areas of your cell and as you get further away from your Access Point, your speed decreases, but this does not mean that you don’t ‘get an 802.11ac data rates’. The 802.11ac specification allows for as low as 6.5Mb/s and as high as ‘gigabit wifi’ and all sorts of speeds in-between. With 802.11b/g/n it was possible to ask for ‘the best, and make it pervasive’ and you could theoretically design an environment to support the highest supported data rates in all locations. With 802.11ac, this is no longer possible due to the very strong signal strengths required and the very wide channels required to achieve ‘max throughput’. It is unreasonable to expect an enterprise wireless deployment to support 1300Mbps (or whatever your Access Points spec sheet claims as the max) in all locations for all clients.
If you ask for an 802.11ac site survey without any other clarifications, you can safely expect massive cell sizes and generally poor throughput which is likely not what you want. Examining your Access Points data sheet will give you some idea of the wide range of signal strengths required (not to mention channel widths) to support a variety of 802.11ac data rates. The Cisco AP3700 data sheet for example, shows that -61dBm is required to support VHT80, MCS 9, 3 spatial streams (the ‘highest 802.11ac’ supported on the Access Point at 1300Mbps) all the way down to -92dBm for VHT20, MCS 0, 1 spatial stream (the ‘lowest 802.11ac’ supported on the Access Point at 6.5Mbps). All of these qualify as ‘supporting 802.11ac’. This wide swing in capabilities is the reason that you cannot simply ask for ‘an 802.11ac site survey’. Instead, you should always start by gathering your requirements upfront:
- What are my throughput requirements?*
- What are my density requirements?*
- What are my client types?*
Then turn those expectations into leveraging a technology for the deployment. If you do not set those expectations upfront, or have a good understanding of what your clients requirements are, how can you claim success? You need to mutually agree upon design requirements, then prove that design back in whatever fashion you agree on. Set expectations, design for those expectations, meet those expectations, then prove that you’ve met those expectations. And please, stop asking for an 802.11ac site survey.
* There are many things that go into a proper RF design, not to mention supporting other applications such as BYOD technologies that I’m intentionally glossing over. This is just a small sampling of some of the questions you can use to suss out your customer requirements and is by no means the only way of doing it.