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Topic Title: What is the difference between 'Data Voice' and 'Location Based' surveys?
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Created On: 01 December 2011 04:18 PM
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 01 December 2011 04:18 PM
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gullanedave

Posts: 102
Joined: 02 December 2005

Hi,

Looking over a tender for a client who is wanting a wireless network(s) installed at some of their premises, and they have requested that the contractor makes recommendations on what type of survey is required, namely; (A) Data Voice Survey, or (B) Location Based Survey.

What are these surveys that the client is speaking of? What is the difference, as they have also asked for the contractors to define the cost differential between them.

Thanks in advance.
 01 December 2011 05:20 PM
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jakegreenland

Posts: 66
Joined: 04 May 2009

From the context of the request I'm guessing this is for 802.11 wireless LAN ? In which case it shoud really be three categories, Data, Voice and Location. [if it's not 802.11 wireless LAN then ignore everything below!]

The three types of traffic place vastly differing demands on a wireless LAN and need a different deployment of access points.

Data typically needs access points strategically placed to provide maximum coverage for the desired client density without the APs interfering with each other to any great extent - it is common for the signal strength to get a little weak at the edges of the coverage area but for data this isn't an issue.

In this scenario the APs typically end up positioned towards the centre of the building for the most cost effective deployment. Surveying this type of deployment is commonly done via the "AP on a pole" method where an AP is positioned on a pole [using a mic stand or just a body to hold the pole] and then coverage is mapped in the area around the AP and then the AP is moved on to a location beyond the mapped coverage and repeated until the whole area has been covered.

For Voice/VoIP traffic the requirement is usually to ensure total coverage with a strong quality signal as weak or bad signal means dropped packets and choppy voice - you also have to deal with the AP roaming issue for a portable handset which means keeping the reassociation time to as low as possible to avoid dropped calls. As a result this means a much greater density of access points.

So when surveying for a voice WLAN implementation a common method is again to perform the "AP on a pole" process but with much tighter criteria for signal strength and also making sure that every nook and cranny where someone might use a phone handset is covered. As a result this usually takes longer.

For wireless location the whole thing is turned on it's head. Location servers track devices by triangulating signal strength of the client from the access points [in some implementations it's measured at the AP, in some it's measured by the client] and using the nkown location of the APs to work out the position of the client device on a map. To do this kind of triangulation it helps to have access points as close to the edges of the building as possible so that positions can be triangulated from the outside walls.

When surveying for wireless location monitoring you'll usually need to use 3 or 4 APs at a time and move them around to get the best points for triangulating clients. Obviously this needs more resources and time.

When mixing requirements then it really ends up at the point where you need a skilled wireless designer/professional who can use judgement and experience to come up with the best balance between the competing demands.

Normally, however, most organisations that tender for these things these days will use a tool like Ekahau Site Survey or AirMagnet planner to load in scale drawings of the site to be covered, then define all the construction types of the walls etc and then the software can use mathematical prediction to come up with estimates of coverage for the varying requirements. You can then use a fudge factor to allow for errors and use the resulting number of access points and coverage areas to come up with a decent budgetry figure.

Hope this helps

-------------------------
Jake Greenland, CEng MIET.
CCIE #22595
 01 December 2011 05:34 PM
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gullanedave

Posts: 102
Joined: 02 December 2005

Jake,

Thanks, and I really mean that.

Your answer is as informative as I could have hoped.

If I can pry for some more of your knowledge I would be most obliged;

Q) Given your excellent answer above, it would seem to me that for this client (who is intent on using the soon-to-be installed wireless system as the main vehicle for connection to their LAN, and is also intent on using it for VoIP) that the 'Voice' or 'Data/Voice' survey they have eluded to would be the best solution, as the 'Location' survey would cost more and take longer, and for what measurable advantage?
 01 December 2011 09:27 PM
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jakegreenland

Posts: 66
Joined: 04 May 2009

No probs at all,

To be honest it sounds like whomever wrote the tender wants the moon on a stick! Typically however yes, what you'd be looking to do is survey for data but allow for the proposed VoIP usage with greater AP density and check for all the odd places people end up using phones [stairwells usually, not somewhere you'd normally have wireless data coverage by default but I've had coverage requested in toilets and changing rooms before!].

The location survey would really be for specific purposes - ie if they wanted to use location tags or track specific devices. Wireless location services has always been one of those solutions looking for a problem in my opinion. The only time I've really seen it successfully used is in hospitals. The general principle is that you place tracking tags on anything you want to keep tabs on and the systems uses the signal triangulation to let you know where it is. There are a variety of different systems for doing this and what they all have in common is they are extremely expensive for what ultimately is some maths and a database.

I would generally suggest that unless the client has a defined requirement for location services there would be no material advantage to surveying for location or deploying APs in a deployment viable for location tracking. [Ekahau, one of the leaders in vendor independent location services, will happily tell you that their system works with any deployment anyway - this might not be entirely true ]

In your circumstances you've got two real choices - do a traditional ap on a pole survey allowing for voice. Gauging the time for these is more art than science relying on past exerience more than anything. Alternatively you could look to deploy a wireless system technology like Meru Networks which has some technological advantages that mean you can get away with a survey performed by the software I mentioned earlier. There are certain partner barriers that may prevent that however pushing you towards the usual suspects.

Aerohive offer a free wifi planning tool at their website that's not bad if you wanted to do some virtual planning first. Feel free to PM me if you need/want to go into any more techincal detail that you can't do on an open forum.

-------------------------
Jake Greenland, CEng MIET.
CCIE #22595
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