AP Placement in Office Building

[JASON SIMMONS]

A site survey was recently completed at my location.  It's your typical office building with sheetrock walls, solid wood doors, and 4' cubicles.  Per the report we need to add somewhere in the neighborhood of 5 to 8 additional APs per floor so we can reduce the power levels and limit interference. Currently all of the APs are the hallways.  The suggested AP placements call for some APs to be placed in offices and conference rooms.

What's the benefit of adding these additional APs placing some of them in offices and conference rooms versus installing the additional APs in the suggested areas but in the hallways?

I've attached the suggested layout of a floor for reference.

[Leo Laohoo]

The major benefits of putting in an AP inside the room, like conference or meeting rooms, means your AP doesn't have to go "far" to reach clients.  The APs signal doesn't have to penetrate walls.  Ok, so the walls ain't made out of concrete or bricks so the signal loss ain't that great, but your AP is there.

[JASON SIMMONS]

Ok.  So it is/can be beneficial to place an AP in a conference room, but putting an AP in a random office isn't necessary?

I've heard that you shouldn't put more than 3 APs within line of sight of each other because they could end up interfering with each other.  I never really understood why.  With newer technology is this no longer a concern?

[Leo Laohoo]

Ok.  So it is/can be beneficial to place an AP in a conference room, but putting an AP in a random office isn't necessary?

Yes and no.  I'm going to separate my response with offices and conference rooms.

The floor is packed with offices.  It'll be downright dumb to put an AP in each office.  So ideally, what you do is space out the AP emplacement.  Let's say you put an AP in the centre and put the next AP two rooms to the left and right.

Another thing why it's ideal to put an AP inside meeting rooms and conference rooms:  Client density.

In meeting and conference rooms, you will get a high density of wireless clients.  It's not the same as offices.  If your room will find use of, say, 25 people then put an AP in them.

Another thing, back in 2011, Cisco has released a study that said the ratio of the number of wireless client per person is 3:1.  This means each person is likely going to have three wireless clients at any given time. 

[CableWiFi]

Leo,

Do you know where that Cisco ration study can be found? I'm trying to find such data (recent too) to properly plan link budgets for a HD deployment.

[Abhishek Abhishek]

Please refer to the design guide recommended by CISCO-

http://www.cisco.com/en/US/docs/wireless/technology/mesh/7.0/design/guide/MeshAP_70.html

[JASON SIMMONS]

The link you posted is about Mesh APs.  Do the same rules apply for a non Mesh deployment?

[George Stefanick]

Jason,

Its a rather complex subject when breaking down CSMA which uses CS and NAV. On the end of the day you want to use survey software to map your area of coverage. You want to make sure your TX power is around 20 - 50 mw on the aps. You dont want to do a hallway design, if you dont have to. When APs on the same channel see each other they will they cause interference.

Think back to the 80s. (not sure how old you are ) . But there was a time when cordless phones came out and when you called a friend, you could hear other people talking on the line. It was because you shared the same channel ob the cordless phone. When this happens in wifi it causes packet tries. The station sends a frame and waits for an ACK. It doesn't get an ACK because it was interfered with by another station. So it has to send it over again.

If you have 2 aps on the same channel. Make sure you are 20 dB different from the other ap.

Here read this blog I did ..

http://community.arubanetworks.com/t5/Technology-Blog/Real-world-examples-and-discussion-around-WiFi-channels/ba-p/66712

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"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
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[Scott Fella]

Here is my 2 cents. The survey seems good from looking at it. I would typically out the AP's in the middle of the room. The AP's in the corner hallways are good too for roaming, but I would be worried about the coverage in the middle rooms I between the two AP's. If the survey was done, I would guess that you do have adequate coverage for what the requirement was for the survey.

Sent from Cisco Technical Support iPhone App

[kaaftab]

Kindly check the following link for wireless deployment

      http://www.cisco.com/en/US/docs/wireless/technology/mesh/7.5/design/guide/mesh75.html

[vlad.mihailov]

For the reasons of adding APs and having them inside of the conference rooms you have seen the answer above.

Now for why the surveyer chose not to have APs in the hallway. I would guess the reason was that they tried to create more or less even attenuation around APs - both in the direction of clients and towards ajacent APs. This makes AP receive neighbors at lower power and helps automatically adjusting the transmit power. When all APs are in hallways they have a better line of sight to each other and Transmit Power Control will likely reduce the power allowing for less power leaking in to the offices between the two APs. I am not sure if the explantion is clear. This is a strategy I use if I have a choice. Certainly in large open areas with many users (like call centers) you simply have no other choice.