Security in Passwords

I spoke with a Network administrator at a school district a few days ago and he was having trouble with passwords being strong enough for the staff. He could not relay a way for them to get good passwords that were hard to crack so he asked me for some help in conveying the message and in coming up with a better way for them to do their passwords.

I creates this alphabet for him and I thought I'd share the idea so everyone can get an idea on  how to avoid having cracked passwords.

Security Alphabet

A = @

B = B

C = (

D = D

E = 3

F = F

G = &

H = #

i = !

J = ]

K = {

L = 1

M = M

N = N

O = 0(zero)

P = ?

Q = %

R = R

S = $

T = +

U = U

V = ^

W = W

X = *

Y = Y

Z = >

For passwords to be secure, you want something you can remember but also something that cannot be looked up in a dictionary.

Create a phrase you can remember:

“Pigs are good” then change the phrase to the security alphabet.

?!&$R&00d

Then you know it can’t be cracked from a dictionary attack.

If you need a longer phrase, then create one:

His socks are smelly

#!$$0({$R$m311y

Or break it up and modify it:

H1$$0ck$R$m311y

I hope this helps you to develop your own password strategy, and remember.... You should change it often.

Brett Hill, CWNE#147

Converting a Light weight AP to an Autonomous AP Using TFTP

     Occasionally, one might need to perform a conversion on an access point in order to use it as a survey tool, or convert a survey AP back to a light weight AP. The problem is this: We don't always do this and it can become very easy to forget the steps needed to be successful at it.

I recently had my Cisco 2602e loaned out to someone performing RF testing on it in a lab so I had to convert a new AP so I could use it to re-survey an industrial area that made a lot of modifications since the last survey.

Lucky for me, I have plenty of people available to reach out to to trigger my memory for such things as many of us do different tasks, and some much more than others. I reached out to Sam Clements, an old friend who is always willing to lend a hand when I need him.

Here are the steps in performing the conversion and I will add the big deal breaker here that I had to get from Sam (A Mac User), the TFTP Server that comes on the Mac doesn't work for this so I used my Mac to console in with My AIR CONSOLE (Love it) and set up my Dell Laptop as a TFTP Server using 3CDaemon (a free download) as my TFTP server program.



Console into the AP using the AIR CONSOLE Bluetooth connection from the Mac
(You can replace this step with simply using the Cisco console cable if you have a serial port on your PC).

 Press the MODE button (on the access point) and hold it down then power up the AP with the button held down.

As you see the AP boot up, the screen will show "Button Pressed. Waiting for release" and you can release the button at this time and the AP will boot into ROMMON mode.

Your first step will be to format the flash by simply typing this command:
format flash:

Next, you want to set up the network with these commands:
set IP_ADDR 10.0.0.10
set NETMASK 255.255.255.0
set DEFAULT_ROUTER 10.0.0.1

of course you can modify the network if you wish but you have to be sure your PC acting as the TFTP server is on the same subnet.

Next, you have to initiate the flash, the ethernet port on the AP, and the TFTP capability using these commands:
flash_init
ether_init
tftp_init

These three steps have to be performed.

Next you will use the xtract function and load your new image to the AP by using the following command string:
tar -xtract tftp://10.0.0.2/apimagename.tar flash:

*Note: the ip address in the string is the ip address of your PC used as the TFTP Server.

*Also note that the ".tar" extension has to be shown on the file of the directory your TFTP Server is pointing to. Type in the ap image exactly as it shows in that directory or you will not succeed.

You will see the file transfer begin, and it will take a little time to do but you are well on your way.

Once the file loads, you will need to reboot the AP and it will boot with the new image.

When you get to the prompt use Cisco for the username and Cisco for the password to log in and begin configuring the AP.

Here are your steps again in order:

format flash:
set IP_ADDR 10.0.0.10
set NETMASK 255.255.255.0
set DEFAULT_ROUTER 10.0.0.1
flash_init
ether_init
tftp_init
tar -xtract tftp://10.0.0.2/apimagename.tar flash:

Hang onto this command string for future use. You'll need it.






Brett Hill, CWNE #147

Coverage Hole Detection

I was asked last week about planning for coverage hole detection in a wireless network. The gentleman said he had a really good survey (design) and the guys that did the design really did a great job with their Air Magnet software and the heat maps proved it.

His problem wasn't the overlap of cells, co-channel interference, or anything like that... His main problem was that the survey was performed at the max power level of his VoIP devices (802.11 wireless phones). In doing so, in the event a coverage hole issue was triggered, the controller was turning the nearby access points up 3dB higher than the max power of the VoIP phones and issues were arising because of it.

The solution is to really go back and re-survey at a lower power level so that when a coverage hole detection is triggered and the controller has to turn the power up on a couple of access points, the power level will not be raised above the max power of the VoIP phones.

In his case, since the installation was complete and the moving of the access points was going to be really costly, we set his VoIP phones to the "G only" setting and allowed lower data rates on the network (Nothing 11MBs and below).

The spectrum analysis showed a clean environment for 2.4GHz and the phones were the only devices using the 2.4GHz band so it worked out great and he had no more issues with his phones.

Another lesson to remember when starting a new design (survey). Always know the devices you are going to have on your wireless network before designing it, and survey at power levels below the max power level of the weakest device you are going to deploy. This prepares you for a coverage hole detection without compromising the integrity of your wireless network.



Brett Hill, CWNE #147

dB to mW Conversion Table

Always remember that 3dB is Half Power in either direction, and the measurements are "Relative".

View the chart below and notice there is another factor of ten (10) hi-lighted in red. This chart will help you understand the back and forth conversions. Some access points show power settings in mW and some show it in dB. It is helpful to memorize the two (2) patterns.

     

     10W           =          40dBm          =          10,000mW

       8W           =          39dBm          =            8,000mW

       4W           =          36dBm          =            4,000mW

       2W           =          33dBm          =            2,000mW

       1W           =          30dBm          =            1,000mW

800mW           =          29dBm                                       27dBm           =      512mW

400mW           =          26dBm                                       24dBm           =      256mW

200mW           =          23dBm                                       21dBm           =      128mW

100mW           =          20dBm                                       20dBm           =      100mW

 50mW            =          17dBm                                       18dBm           =        64mW

 25mW            =          14dBm                                       15dBm           =        32mW

12.5mW          =          11dBm                                       12dBm           =        16mW

10mW             =          10dBm                                       10dBm           =        10mW

6.25mW          =           8dBm                                          9dBm           =          8mW

3.125mW        =           5dBm                                          6dBm           =          4mW

1.56mW          =           2dBm                                          3dBm           =          2mW

     1mW          =           0dBm                                          0dBm           =          1mW

Brett Hill, CWNE #147 

Understanding Milliwatt to dB conversion in the Wireless Survey

     Decibel to milliwatt conversion is important in most every aspect of 802.11 wireless. We use it for antennas, cable loss, signal amplifiers, radio transmitters, etc..

     One place that we do not always apply this knowledge and understanding is in the design stages of the wireless network. Particularly in the survey.

     Depending on the data rate you are wanting to provide to all of your devices in the network, you will survey accordingly. We have to understand that every three (3) dB gained or lost in our rf signal is a direct result of half of our power being gained or lost.

     For example: A transmitter set to 20dB power output is transmitting 100mW of power. If we transmit at 17dB, then our power output is cut in half to 50mW. That is a drastic difference to several applications and devices in 802.11 wireless based on the circumstance.

     If you are using the Air Magnet or Ekahau survey tool to design your wireless network, you have to pay close attention to your measurement tools provided:

RSSI - Received Signal Strength Indicator - The signal from your transmitter

     Noise Floor - Other devices in the area causing a signal to be detected on the frequency you are surveying with.

     SNR - Signal - to - Noise - Ratio - The difference between the signal level your transmitter is transmitting and the signal received from the noise floor created by other devices.

     The SNR is your usable signal and it is read in a positive decibel number compared to milliwatts. The RSSI and the noise floor are both read in a negative decibel number compared to milliwatts.

     If you have a RSSI level of -70 and a noise floor of -92 then your SNR is the difference between the two numbers 22 and it is read in decibels compared to milliwatts (22dBm).

     Where the understanding of the conversions comes into play is when your RSSI or the Noise Floor changes: -67 RSSI and a Noise Floor of -89. you still have 22dBm as a SNR. If the measurement of the RSSI is -64 on the meter, then you naturally think you have a better signal strength, but if the noise floor changes, then you have to factor in the change in the Noise Floor before believing you have a good signal for your design.

     Remember, the SNR is the signal that really matters, and a 3dB difference in that effects your power by half. Sure the industry standard for Voice over wireless is a -67dB RSSI at the edge, but that is assuming a noise floor of -92dB or better. That's a minimum SNR of 25dBm.

     If the Noise Floor goes from a -92dB to a -89dB then you have lost half of your power and that can have serious effects on certain applications in your network.

     If your Noise Floor gains 1dB then you should increase your RSSI gain by 1dB to compensate for it. This is why most all survey engineers go ahead and survey for a RSSI of -65dB in the event that the Noise Floor fluctuates. It gives you a safety zone for your SNR because that is the number that really matters.

    This is why a Spectrum Analysis is Imperative before starting your survey. You have to identify the noise floor you will be dealing with before you can provide a good design.

     Remember***
     3dB changes your transmit and/or receive power by half. This can lead to one way audio at times and it can lead to a downshift in data rates on either transmit, receive, or both. Keep your mind on the math as you survey.

Time Difference of Arrival

     How does TDoA work?

     The best way to describe TDoA is to give a reference of yourself and the way you hear things. The human ear is very remarkable by nature because it is used by the body to turn the head and eyes toward a sound that is heard. The really cool thing of this is that both ears hear the sound and process it over and over as they hear it (if it repeats or sustains). The reason why we are able to turn and look at what caused the noise is TDoA.

     Time difference of arrival is math calculations that take place on frequencies heard by both ears to determine which ear is closer to the frequency, which direction the noise is coming from, and how far away the noise is.

     When both ears hear the noise and the left ear heard it 5 micro seconds before the right ear heard it, then the math begins to direct the eyes to the left because TDoA determined that the noise came in to the left ear quicker than it did the right.

     The TDoA calculations in 802.11 wireless location services operate similarly in the same manner. The signal from the same transmitting device is picked up from multiple access points and/or antennas and the calculations determine which access point the device is closer to as well as the direction the device is from each access point, resulting in calculating the location of a device.

   There are several more cool factors in location services, but hopefully you now have an idea of what TDoA is and how it works.

Deploying Cisco WIPS - Overlay vs Integrated

When making choices about security for your wireless network, there are some ups and downs about everything you are going to have as options.

     When deploying a Wireless Intrusion Prevention System, you should look into the abilities of both types of deployments to see which one is going to work for your environment.

     Overlay WIPS- an overlay deployment is specifically a whole different set of access points designated to intrusion prevention only. In other words, after you have surveyed and designed the wireless coverage for client devices to access your network, you will go back to your floor plans and design a WIPS network that consist of a totally different set of access points deployed within the same area as the wireless network.

     These WIPS access points will be deployed in monitor mode, then you will check the enhanced WIPS engine check box and choose WIPS in monitor mode optimization. You will then click save and you will be prompted to reboot the access point.

     ***Take note that you will have to disable the radio and admin status of the radio before configuring these settings. After you are done and the access point comes back up, you will need to enable both the radio and admin status.

     The overlay option of deployment places the WIPS access points in a full time spectrum scan so that all channels can be scan on a continuous basis.

     The Integrated option only scans part time, and that is only in between transmissions of data. If the access point is in use, the WIPS scan is not working and the network has a level of vulnerability. Also, when the access point is scanning in between transmissions, it doesn't always have a chance to scan all channels. It will only get through a few channels before it comes back to service client data again.

     ***Note  Integrated is also often referred to as a WIPS deployment that controls its WIPS access points and its infrastructure access points all on the same controller. Many WIPS deployments (especially those for a large campus) will have separate controllers for each deployment. One for the infrastructure and one for the WIPS deployment. This is the most expensive option but is also the best approach to utilizing WIPS.

I've provided a Cisco link to the configuration of WIPS below:
http://www.cisco.com/c/en/us/td/docs/wireless/mse/3350/7-0MR1/wIPS/configuration/guide/wIPS_70MR1/msecg7x_ch6_wIPS.html

Can My design include signal propagation through steel grate floors to the lower level?

     The $5 million question.....

     Throughout the development of 802.11 wireless advancements, signal propagation has been questioned, tested, and requestioned in numerous scenarios. Fact is that in the earlier developed technologies refractions and reflections produced noise and interference against the original transmission, but now with MIMO and its abilities, reflections are used to the advantage of the transmission.

     The reflected signal ultimately is out of phase and has fallen behind in time of arrival when compared to the original transmission, but now the two or more signals (main and out of phase reflections) become combined and used as multiple paths to transmit data packets on. When the reflected signal shows up at the target device say... 10 micro-seconds after the primary signal, then the primary signal is slowed down to be synchronized with the reflected signal. MIMO uses reflected paths to its advantage to transmit more data faster.

     As far as the grated floors, the reflected signals work out the same way, but you do end up with a smaller RF footprint (coverage area) below due to the many unusable reflections.  You should use your survey software on the lower level and measure the RSSI against the noise floor and packet losses and you will find the dependable area of coverage in a clean SNR with little to no packet loss. By no means is this area as big as the area covered on the upper floor, but it is absolutely dependable for VoIP grade coverage and can and should be incorporated into your overall design for access point placement. If you don't use this area, then you will end up with a very non-standard overlap in your cell coverage and VoIP will most likely suffer because of it.

     VoIP works great at or around 20% overlap and this overlap needs to remain consistent across your design. 20% on one the 5% on another and 35% on the next will cause roaming issues for VoIP clients so any bleed through from floor to floor should be factored into the design to avoid issues.


Brett Hill, CWNE #147

Dropping calls on outdoor Mesh Deployments

     This is a topic that I have dealt with for about 4 years during a government project deployment. Dealing with outdoor mesh deployments for the most part are relatively simple and hassle free, but there are some issues you will encounter and problems with VoIP is a hot topic.

    Problem Encountered

     When doing post installation testing of your outdoor mesh, you would typically want to use the VoIP phone and walk around the covered area, roaming from AP to AP, doing a "Can you hear me now?" commercial. By grabbing a couple of the phones (remember... designing for the devices to be used on the network is the best way) and placing a call between them, one person can walk the coverage area while the other monitors the call from an office somewhere. The non-mobile person will monitor the clarity of the call and pay attention to any moments where one side or the other cannot hear the other, and also take note of any dropped calls and where the call was dropped.

     Lightweight AP design Glitch

     When deploying mesh networks in a lightweight scenario, the controller sets the channels and the power just as it does for indoor deployments. Here is where the glitch is:

     Indoors- the access points typically see each other in a relatively familiar pattern as the devices would pick up on them such as walls between them, high shelving, etc..

     Outdoors- the access points mostly have a clear line of sight to each other because of the deployment model, while the devices themselves dwell at ground level between the buildings and other obstacles.

Why does this matter? Roaming.

   Unless you are in a single channel architecture model, wireless devices will not roam across identical channels. Each access point that the device roams to has to be on a different channel than the one it is roaming from in order to hand off the connection without dropping it. This presents a problem with outdoor mesh deployments sometimes because the actual walk Path of the user varies significantly from actual coverage that the access points monitor from the roof tops.

     There will come a time that calls will be dropped because your device is traveling from (scenario) say a channel 1 to a channel 1, or a channel 36 to a channel 36.

     As an engineer, you will have to use something like Google maps and place all of your outdoor access points on the map, then view and even physically walk the area, locating all of the most common walk paths within the deployment coverage. This will help you identify how to manually set channels to avoid any of your walk paths containing a same channel roaming issue.

     I have had to do this several times over the past few years to avoid dropped calls due to same channel roaming. I have attempted to tweak the sensitivity on the Auto channel option but it still had issues, and the best way to ensure the problem stayed away was to manually configure the channels and leave the power settings to my RF profile within the AP Group.

Note***

     If you performed your survey correctly, ran a spec an of the area to identify and remove any interferers, and your power levels along with proper cell overlap is all correct, take a look at the channel situation because a controller does not take "Walk paths" into consideration when setting channels automatically.

Brett Hill, CWNE #147

Priming your Cisco access points before deployment

     Access point deployment can become a huge problem if your environment is one where an engineer designs, an admin configures, and a tech deploys, while a group of electricians pull the CAT5 or CAT6 cable. Too many hands in the deployment makes for multiple opportunities to have complications. It will also prove to take longer to resolve issues when troubleshooting.

     One great way to rule out the access point itself as the problem (if problems arise) is to prime the access points before handing them off to the Tech for deployment.

     When priming an access point, you take care of a lot of things up front that could go wrong in the field. One is code upgrade.

     When an access point comes out of the box, it may or may not have the same code your controller is running. Once an access point comes up and finds a controller, it upgrades or downgrades its code to match the controller it has associated to. You can do this before  deployment and avoid errors by handling it in a controlled lab environment.

     Naming the Access Point

     Another thing that is pretty cool to do ahead of time is naming the access point. Outside of placing a label on the access point, you can also name it so that when it comes up in the controller you can match it with your design document and know that that one particular deployment was successful. This will be of great help to you in large deployments. Especially those where you have multiple facilities over a large campus. Your design document should reflect access point models and names so you can reference the name latter if troubleshooting needs to take place. Quickly identifying an access point will speed up your troubleshooting process.

     Redundancy

     Another option is setting primary, secondary, and tertiary controllers for each access point. With the HA pairing option now, not many are using these options, but it is still a good fail safe to set in place in the event the HA pair may glitch on you. (can't have too many redundancies). I say if it's available, use it.

     Type of deployment

     During the priming stage, you can also pre-set an access point to a local mode access point, or several other modes available for deployment that allows an access point to monitor the network. It is good to pre-set these modes and verify they are correctly set before handing the access points off to the tech staff for deployment.

     Mesh Access Points

     When deploying Mesh access points, you have to pre-configure some things before the controller will recognize some access point models. The 1520, 1530, 1550, etc... all have to be added to the MAC Filtering table under the security tab before they will come up on your controller. This is a security feature that helps protect against rogue access points joining your network through your mesh deployments.

     Priming the mesh access point allows you to set the AP to a root or non-root AP before sending it to the field and you can even test the bridge connectivity to verify the two will communicate.

     By performing these priming steps in a lab environment, you can be confident that the access point isn't the problem once it is deployed and problems arise. You also have name comparison to help locate APs during troubleshooting sessions, and when deploying bridges, your priming stage has already verified communication between the two units before they are installed.

    Ruling out Just a BAD Access Point

     Not often, but sometimes an access point will come out of the box with a defect of some sort that needs to be addresses. I have wiped the flash and reloaded it in order to fix out of the box issues, but not all the issues can be fixed. You don't want to send an access point into the field and it come out of the box defective and your field tech stuck with dealing with it. You will wind up walking them through this remotely and probably still face delays by getting a replacement sent out anyway.

     Priming the access points will eliminate sending defective units out for deployment.

     If you don't prime, you're wasting time. Safe yourself and others a lot of headaches up front.


Brett Hill, CWNE #147

Cisco Users... Why Use RF Profiles?

     I was doing a kick off meeting in a power plant and explained the whole project design and was asked the question "Why use RF profiles?" The argument from the other person was that the device itself makes the decision on when to roam, so why bother?

     When designing a wireless network, you set the survey AP at or below the power of the devices to be used on the network. Setting up RF profiles allows you to keep all of your access points at those power settings after deployment and then some.

    An RF profile is applied to a group of access points of your choosing. This profile can have many parameters set to maintain certain controls over the access points and two of them are the power settings and the data rates.

     Like I mentioned above, the power settings on the access points need to be at the level they were when you surveyed or the survey is void. You can't survey at 14dB and then allow the access points to operate at 17dB or 20dB (and if you do, there is a sign there that your survey could have flaws). The survey itself should reflect what the live deployed network is going to look like. The RF profile will help to accomplish this.

     You can set the power in the profile to the 14dB limitation just as the survey was performed at, and you can also set a minimum power that you do not want the access points to drop below. Beyond that, you can also control the data rates allowed per access point.

     If you surveyed correctly for a VoIP deployment and set your cell edge at -67dB or -65dB, then you do not want to allow any data rated on your network that can be achieved at a lower dB level (check your access point's specification chart to see these levels). Mostly, a -67dB cell edge would not allow for any data rates below say a 56MBs rate so you would want to turn off 48MBs and below in your RF profile.

     What does this do? It does two important things worth mentioning right away....

     1) it maintains the original cell size that you surveyed for.

     2) it maintains excellent throughput per client device.

     How??????

     Maintaining the original cell size is done by holding the allowable data rates at what you surveyed for. If 48MBs or 36MBs were allowed on the access point, then the actual cell size would be bigger than the one you surveyed for at -67dB. If you do not turn off any data rates and allow for 11MBs and below, then the cell size is 4 and 5 times larger than the one you surveyed for at -67dB.

    Why?????

    The data rates are all based on proximity and modulation type to say the least. There are other factors such as noise floors, co-channel interference, etc... but lets look at the proximity and modulation types.

     When an access point transmits through the air, there is a factor called free space path loss that plays a role in degradation of the signal. The lower the signal, the lower the dependable data rate becomes. Once a lower dependable data rate is chosen, it is more than likely because a different modulation type has come into play in order to get that dependable data rate at said distance.

     Now... if you do not allow those lower data rates on your network, then all devices have to be at a closer proximity to the access point in order to connect to it, and they are forced to connect at only the higher data rates allowed on the access point. but guess what else happens........

     By forcing the lower data rates out and forcing the client devices to only use higher data rates at a closer proximity to the access point, you are also forcing the client devices to roam quicker than they normally would.

     Wait!!!!! Did that come out right????? An access point forcing a client device to roam?????

     Yes. By controlling the data rates, you control a portion of the roaming as well. A device can no longer be sticky and hold on to its original associated access point until it rate shifts all the way out to 1MBs because you don't allow 1MBs on your network. The device can rate shift from 150MBs (if available) down to 54MBs and then it has to roam to a neighboring access point before the original access point's signal drops any lower as it moves away from it.

     Ultimately.... You have controlled the health of the wireless network by having less clients per access point and they are staying connected at higher data rates.

     This all results in a better customer experience, and that is great for you.


Brett Hill, CWNE #147

What we can expect from 802.11ah

     The Term HaLow is no longer one pertaining to just an energized gaming console. The IEEE has release a new standard for us to work with and all I can say is "ah........"

     802.11ah is a low powered frequency living in the 900MHz realm (902 - 928MHz). These signals will penetrate walls, doors, pictures, TV sets, and other obstacles a lot better than our usual 2.4GHz and 5GHz signals.

     One great thing is the power consumption savings. The signal isn't degraded as much as it passes through objects in its path so devices use less energy when transmitting and receiving information.

    For cities, counties, states, and federal.... The low power and extended range will allow monitoring of gates, doors, roads, bridges, buildings and more.

    What we citizens can expect to see this protocol do for us is:

- it will be a way for our cars, trucks, TVs, fridge, microwave, watches, etc.. to communicate and update us and/or the maintenance man about troubles and parts needed to fix them. Also it will simply be a notification signal used for driveway sensors, mailbox doors, etc.... lol

     You name it and the possibilities are endless, and it will possibly become an alternative to BlueTooth.

     Since the 900MHz signal can propagate much farther than the 2.4GHz signals, we will get better distances leading us to more home options for tech-savy gadgets around the home.

   Get ready to be the Internet Nerd and replace all of your appliances with IPv6 capable Wi-Fi appliances and completely automate your home for the future.

Remote control Coffee Makers, dish washers, kitty litter boxes, and more... lol

     802.11ah the "Wave" of the future.


Brett Hill, CWNE #147

Providing a good wireless design for your customer.

     While attending conferences and seminars, I have been approached by several attendees inquiring about doing a proper survey. Many who believe they are performing surveys correctly are still not even getting close to a proper design.

     As I mentioned in a previous blog post, the applications that will be used on the wireless network are very important to have before you start your design. Surveying for a data only hot spot is simple and requires little to no ability at all, but if you are looking at having location services and/or VoIP on your wireless network then you must know what you are doing in order to provide proper coverage to your customer.

    Let's start with the basics of setting up for your survey:

1) What devices (type of VoIP phones and or/location tags) are you going to be using?

2) What is the expected customer experience?

     Before you begin a survey, the actual devices to be used on the wireless network would be a great thing to know about. Each device is designed slightly different and you could get a VoIP phone with a single antenna with no diversity, or you may have one with a higher output and diversity. Without the specs on the phone, you are taking a risk of designing a network that your customer will experience problems with while using their devices.

     You should always ask the customer what they see as an end result of getting a wireless network. Let them tell you what they expect their experience to be. Don't go in with a cookie cutter approach and tell them what you intend to do and what their network will do when you finish. If the customer has pictured a certain experience in their mind, ask them to share that though with you so that you can set out to provide that experience if its possible.

     Lets look at the actual survey now.

     Based on the customer's vision, you now have to survey the facility with the limitations of their wireless devices in mind. If their VoIP phones will only transmit at 30mW then you do not want to go in and survey with your access point set to full power. This will spell out problems for the voice network and the customer's experience isn't going to be good.

    It is always good to set your network's transmit power at or below the power of the devices on the network. Since the VoIP phone is the most crucial and lower power than laptops, use the phone as a measuring tool to set your survey transmit power. This way you are not designing a network that transmits more powerful than the devices on it.

     How to survey correctly

     If you are using a survey software like Air Magnet or Ekahau, then you have tools in the software that allows you to adhere to standards during the survey. For example.. Above we spoke of surveying for a VoIP network so you need to know what the minimum cell edge requirements are for the VoIP phone you will be using. If the minimum signal requirement is -67dB then you can set the software to display a gray area for all locations surveyed that do not meet that requirement. If you do not use this tool, then you will have no idea where the edge of the cell needs to stop because the software will continue to pain the floor map in colorful schemes until you reach -100dB signal and disassociate from the survey access point (average default setting to disassociate;may vary). If you want to really see the device requirements met on your floor plan, you will use this option to display the boundary as you survey. Then...

   You can display the footprint of the first access point's coverage and make a great determination as to where the next one will need to be. Survey the next access point with the required 20% average overlap of cells and then combine the two footprints to see how much area you have surveyed and how much you have left. Continue this until you have all of the required areas surveyed properly and then combine the total coverage into a single drawing and look for gray areas on the floor. If none exist, then you are off to a great start.

     Surveying has a lot more involved in it than what I have posted, but I have provided the basics here. I look forward to seeing your experiences in your comments and input.

Brett Hill, CWNE #147

Questions about wireless access points and how many users you can expect to have on each one.

     Over the last few days, I have read dozens of posts pertaining to the number of users an access point can have on it at any given time. The responses have been overwhelmingly diverse to say the least but one thing is certain in all of them... There is no concrete answer to this question. In fact, most of the answers folks were providing had a lot to do with a manufacturer's chipset or the 802.11 protocol's statement allowing for 2007. The truth is that this is a loaded question waiting on hundreds of educated wireless experts to tear it apart. I am going to make a few statements about this question and then ask those experts to contribute to the information.

     First off, there are only suggestions from various manufacturers of 802.11 wireless access points as to how many users can be on each access point. These suggestions are no less than a sales point to allow a number to be mentioned. You can not designate a number of users per access point until you at least answer several other questions:

1) What applications will you be using on your wireless network?

2) What security measures will be in place on your wireless network?

3) What does the environment look like and what is in the environment that could effect signal?

4) How much area are you wanting to cover with a single access point in this environment?

5) What data rates are you going to allow on the wireless network?

and the list goes on and on..... but these are a few questions that NEED to be answered.

     The application is both processor and bandwidth reliant. What I mean is.... an application may require a lot of processing power and bandwidth, depending on the application. These two factors alone weigh heavy on the individual access point when you are talking multiple clients using the same application on the same access point.

     Securing the network takes processing power and bandwidth overhead. Off course you can avoid the use of this overhead by not using any security but your network will not be safe at all.

     The environment plays a role as well. Interfering devices can cause a higher noise floor in cases and the end result would be any of many things including rate shifting,  and using a less efficient modulation type to obtain a stable connection.

     If you want to cover a lot of area with your access point, chances are you are going to turn up the power by increasing the transmit power, using more powerful antennas, or a combination of the two. This could be tricky because of client power limitations and it could result in an array of issues. The Near/Far effect could occur, contention for the network could take longer due to the amount of users now in the cell and the data rates they are connected at. (just a few... I want to leave plenty of room for input here).

    Data rates are a big topic. If data rates are not controlled based on applications used, then the network is opened up to a multitude of issues. Clients closer to the access point will connect at a better modulation type and better data rate while those clients further away will use a different modulation type in order to secure an efficient connection resulting in lower data rates. If devices are allowed to connect at "B rates", then the whole network suffers the consequences of having to slow down to sync up with the slower slot times used by the single device utilizing the "B data rate".

     All of these are factors that play with the math. If you are going to use wireless as a network connection, you must assess the needs, applications, security, etc.. before you determine how many users you feel will efficiently operate on each access point.

Brett Hill, CWNE #147