Adding Access Points

 

Adding Access Points

Expanding your Wi-Fi hotspot by adding APs mainly involves finding the right places to set up the APs within your facility and figuring out how to wire them back to the network.

APs are similar to wireless routers and hotspot gateways in the sense that they all provide wireless connections to end users. APs, however, do not provide routing or hotspot features, because these features are not needed.

Figures 12-8 and 12-9 illustrate the difference between a single wireless router or hotspot gateway network and an expanded network using APs.

Figure 12-8. Example of a Single Wireless Router/Hotspot Gateway Network

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Figure 12-9. Example of a Network Expanded with APs

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Adding APs to your hotspot network gives users a larger coverage area to make a wireless connection to one of the APs, which are connected to the main network, as shown in Figure 12-9.

Preinstallation Site Survey

The first task when expanding your hotspot with multiple APs is to conduct a preinstallation site survey. This is necessary because with wireless systems, it is difficult to predict the propagation of radio waves and detect the presence of interfering signals without the use of test equipment. Even if you are using omnidirectional antennas, radio waves do not really travel the same distance in all directions. Instead, walls, doors, elevator shafts, people, and other obstacles offer varying degrees of attenuation, which causes the radio frequency (RF) radiation pattern to be irregular and unpredictable. As a result, it is often necessary to perform an RF site survey to fully understand the behavior of radio waves within a facility before installing wireless network APs.

Performing a site survey can help you find the right places to set up the APs within your facility, wire them back to the network, and detect potential interference. The steps for performing a preinstallation site survey are as follows:

Step 1.	Gather the necessary items.
Step 2.	Define the network requirements.
Step 3.	Mark up the building diagram.
Step 4.	Determine the AP locations.

Step 1: Gather the Necessary Items

You should gather all the items you will need during the site survey:

• Facility diagram Locate a set of building blueprints or diagrams. If none is available, prepare a floor plan drawing that depicts the location of walls, walkways, and so on.

• AP You need to obtain one AP (the test AP)preferably the exact AP model and similar configuration, such as the same antenna and transmit power levelsthat you will use throughout the facility.

• Extension cord You will likely need an extension cord so that you can plug in the AP at different points within your facility, without being limited by the location of electrical outlets.

• Laptop or PDA You need a laptop or PDA so that you can properly test the AP locations you will estimate.

• Site survey software You need to load a wireless LAN site survey tool, such as NetStumbler, onto your mobile device so that you can properly measure RF information to estimate AP locations.

  Many wireless adapters come with their own site survey tools. These should be fine for use during your preinstallation site survey; however, make sure the tool shows channel information, because some do not have this feature.

Step 2: Define the Network Requirements

First you must define the requirements for your hotspot network. Defining these requirements can help later when you are performing the physical site survey testing to ensure that you achieve the amount and quality of coverage you want for your Wi-Fi hotspot.

• Coverage areas Mark the areas on your facility diagram where you want hotspot coverage within your facility.

• Quality of connection To find the quality of connection that is best for your situation, think about the number of congruent users and traffic types that you except at your hotspot. You can refer to Table 12-3 for help. After choosing the quality of connection, make note of the recommended signal-to-noise ratio (SNR) in Table 12-3, because you will need this later in the site survey process to ensure good signal coverage.

Table 12-3. Quality of Connection Definitions

Quality of Connection	Estimated Congruent Users	Estimated Traffic Type	Recommend SNR (for Use During Testing)
Good	Up to 5	Light use for e-mail, casual browsing, and so on	15 dB or more
Very good	5 or more	Heavy use for downloading, using Internet phones, and so on	25 dB or more

Step 3: Mark Up the Building Diagram

On the building diagram, mark the areas where you want hotspot coverage, and write in the connection quality minimums for each area. Figure 12-10 provides an example.

Figure 12-10. Example of a Marked-Up Building Diagram

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Step 4: Determine the AP Locations

This is where the real site surveying begins. The following sections describe the procedures to follow to accurately determine where to place APs.

Estimate an AP Location

Consider the location of hotspot users and range estimates of the wireless products you are using and the range of any other wireless infrastructure devices (APs, wireless routers, or gateways) in the area. Then pick out a location within your facility that you think would be an ideal spot to place an AP.

Typical indoor AP ranges can vary anywhere between 100 to 300 feet in all directions. Keep in mind that the interior building construction greatly determines the actual ranges you will experience. For example, you would have a much longer range from an AP in a building that was constructed mostly of drywall than a building made of concrete and steel.

In addition, think about the area in which you are placing the AP, such as the number of walls and barriers around. For example, if you are placing an AP in an open space, such as a fairly large waiting room or auditorium, you will likely see a longer range.

Plan for some propagation overlap among adjacent APs, but keep in mind that channel assignments for APs need to be far enough apart to avoid interaccess point interference, as discussed in Appendix A.

Plug in the AP at an Estimated Location

Plug in the test AP at a location, and remember to place the AP in a similar position that it would be in if you were to permanently mount it at that location. Keep in mind that you do not need to provide Internet (or network) access to the AP at this time.

Take Measurements

In these steps, you use your mobile device loaded with a wireless LAN site survey tool, such as NetStumbler, or your wireless adapter tool, and move around the location while monitoring the site survey tool's measurements, particularly the SNR, to ensure that your estimated AP location is good.

As you walk varying distances and directions away from the test AP, check the SNR measurement from the site survey tool. Consider your desired SNR, such as the recommendations in Table 12-3, when determining the AP's range. The recommended SNR value is a minimum level that you should measure. Good signal coverage exists when the SNR is at or above the recommended SNR value. Mark on the diagram the test AP coverage boundary, based on the desired SNR. See Figure 12-11 for an example.

Figure 12-11. Example of Estimated SNR Coverage Boundary of the Test AP

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In a multifloor facility, make sure you perform tests and mark boundaries on the floor above and below the test AP, such as those depicted in the next section in Figures 12-12 and 12-13.

Ensure That the Test AP Placement Is Optimum

Ensure that the AP is placed in an optimum location based on the SNR measurements throughout the test AP coverage area. Also consider your desired user areas, any overlapping with other APs, and the power and network connection required.

If a certain user area within your facility requires multiple APs to provide adequate coverage, ensure that you have optimum coverage overlap (about 15 percent) with the adjacent APs, or wireless routers and gateways, already measured and noted on the facility diagram. Overlap the coverage of each AP based on your desired SNR, as illustrated in Figures 12-12 and 12-13.

Figure 12-12. Example of Optimum Coverage Overlap: Floor 1

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Figure 12-13. Example of Optimum Coverage Overlap: Floor 2

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As you see in Figures 12-12 and 12-13, the SNR coverage boundary (based on 15 dBm) of AP 1 just meets up with the wireless gateway SNR coverage boundary (also based on 15 dBm.) However, at the same time, ensure that you will not have excessive overlapping.

After you have planned several AP locations, this requirement will become more difficult. That is because you have to ensure optimum coverage overlap with all the adjacent APs:

• If the test AP location is good Double-check that you have marked, on the diagram, the SNR coverage boundary of the test AP. In addition, make note of any electrical outlets and any noticeable routes to run Ethernet cabling to provide power or a network (Internet) connection to the AP.

  Repeat these steps until you have achieved the desired coverage as noted on the facility diagram.

• If the test AP location is not good Based on the SNR measurements you have seen around the test AP location, move the AP and repeat the steps to find an optimum AP location.

Assign AP Channels

After you have identified where all the APs will be located throughout your facility, to provide sufficient coverage in your desired area(s), you must properly assign channels to each AP.

As discussed in Appendix A, you should use only channels 1, 6, and 11 among all your APs. In addition, make sure the coverage of APs that are set on the same channel does not overlap. Overlapping causes interaccess point interference, which you should try to avoid. Figure 12-14 illustrates AP channel assignment.

Figure 12-14. Example of AP Channel Assignment on the Building Diagram

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Make sure you write the channel assignments on the building diagram for each AP. Also, number the AP locations to make the later installation easier.

Network and Power Connection Options

You can connect the APs, which will be mounted throughout your facility, to the network in a few ways to receive Internet access and a power source. The preferred network connection method is Ethernet cable, because it provides the highest-quality connection. In addition, you can use Ethernet cabling to provide a power source to your APs, instead of plugging them into an outlet or running new electrical lines. This technology is called power over Ethernet (PoE).

If running Ethernet cabling through the facility is not feasible, you can use existing electrical outlets for your network connection. See Table 12-4 to help figure out which method to use.

Table 12-4. Comparison of Network Connection Options

Method	Typical Data Rate	Price	Maximum Distance
Electrical wiring	14 Mbps	$40$60 per bridge	200300 meters (or 656984 feet)
Ethernet cabling	10 or 100 Mbps	$5$15 for 50 to 100 feet	100 to 350 meters (or 328-1148 feet)

Power Lines

With proper adapters or bridges, you can use the existing electrical wiring of a facility to send and receive network data, as depicted in Figure 12-15. This provides many places where you can plug APs into the network, eliminating the need to run new Ethernet cabling throughout the facility. HomePlug is the leading industry alliance that provides certification for power line networking devices.

Figure 12-15. Example of a Power Line Network Providing Network Connection for APs

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HomePlug-certified devices have a typical data rate of up to 14 Mbps. That is much lower than Ethernet cabling, which can typically support 100 Mbps or higher. However, the speed of HomePlug is still much greater than common Internet speeds, which range from 300 kbps to 4 Mbps. Therefore, using power line networking devices provides a feasible alterative to installing and using Ethernet cables to provide a network or Internet connection around your facility to plug in APs.

Bear in mind that power line networking devices typically need to be within 200 to 300 meters (or 656 to 984 feet) of each other and within the same phase of the electrical distribution system (or on the same electrical lines) to work properly. Before getting too far with your hotspot installation, you should test a pair of power line bridges to confirm that they will connect to each other and work as intended.

Power line networking devices generally use 56-bit Data Encryption Standard (DES) to help prevent people from plugging into your electrical system to eavesdrop. They also typically have a built-in surge protector. These devices might be affected by other components that are plugged into the electrical system, such as hairdryers, electric drills/saws, vacuum cleaners, and window-mounted air conditioners.

Running Ethernet Cable

As mentioned earlier, the use of Ethernet cable is the preferred method to provide APs with a network connection.

A few different types of Ethernet cabling exist. Your best bet is to use unshielded twisted-pair (UTP) Category 5 enhanced (CAT5e) Ethernet cabling. In addition, you can choose from two different types:

• Stranded Stranded cable has several small-gauge wires in each insulation sleeve, making it more flexible and more suitable for shorter distances, such as 30 feet or less.

• Solid Solid cable has one larger-gauge wire in each sleeve, thus providing better electrical performance than stranded cable. This cabling is traditionally used for permanent installations, such as inside walls and through ceilings. This is also the recommended cabling to provide network connections to your APs throughout your facility. However, keep in mind that this cabling is not as flexible. You need to take proper care of it as recommended by the manufacturer or retailer. When dealing with this type of cable, you should try not to create sharp bends or kinks.

Choosing and Purchasing Your Equipment

When you are looking for the equipment for your AP expansion project, consider using the products recommended in this section. These products are not usually available at local consumer electronics stores. Try purchasing them on Internet stores such as Amazon.com or Buy.com.

Access Points

Make sure you order the correct number of APs for your expansion, which you should know after completing the preinstallation site survey. Figure 12-16 shows the recommended AP that you should purchase. Typical cost for this AP ranges from $60 to $80.

Figure 12-16. Recommended AP: Linksys Wireless-G Access Point (Model # WAP54G)

Power Line Devices

If you will use this method to provide the network connections for your APs, use the information from your site survey. Take some time to carefully examine your facility to determine which and how many power line devices you need based on the power line manufacturer or vendor installation guides so that you can give each AP a network connection. You likely need one bridge to connect the Internet to your power line network and a bridge for each AP.

For more information about HomePlug-certified power line devices, refer to their website at http://www.homeplug.org.

Figure 12-17 shows the recommended power line bridge that you should purchase. Typical cost for this device ranges from $50 to $100.

Figure 12-17. Recommended Power Line Bridge: Linksys Instant Power Line EtherFast 10/100 Bridge (Model #PLEBR10)

Ethernet Cable

If you will use this method to provide the network connections for your APs, use the information from your site survey and devote some time to carefully examining your facility to determine how many Ethernet cables you need and of what lengths. Make sure you order prefabricated or custom cabling unless you want to take on the task of wiring connectors yourself, which is difficult for someone who has not done that before.

You can order Ethernet cabling at online stores such as these:

http://www.cat5ecableguy.com

http://www.ramelectronics.net

http://www.lanshack.com

PoE

If you will use this method to provide power to your APs rather than plugging into regular electrical outlets, use the information from your site survey. Devote some time to carefully examining your facility to determine which and how many PoE devices you need based on the PoE manufacturer or vendor installation guides so that you can give each AP a combined power and network connection.

Figure 12-18 shows the recommended PoE adapter kit that you should purchase. Typical cost for this device ranges from $35 to $70.

Figure 12-18. Recommended PoE Adapter Kit: Linksys 12-Volt PoE Adapter Kit (Model #WAPPOE12)

Configuring the APs

Before installing APs throughout your facility, configure them at a staging area. You can begin by assigning the location numbers to each AP with a permanent marker, sticky note, and so on so that you can properly configure the channel assignments.

• Same SSID You should set the same SSID for all the APs that will be a part of your wireless network or Wi-Fi hotspot. This allows users to roam seamlessly over your entire hotspot network.

• Assignment of proper channels Be sure to set the channels based on the assignments you made during the site survey and the numbers attached to or written on the APs.

• AP isolation Although this feature is not common in all APs, when enabled, it provides some extra security to the hotspot users. It works by isolating users from each other and prevents people from accessing each other's shared files.

  You usually find this feature in the advanced wireless settings. You can usually turn it on and off.

Physical Installation

You are almost finished! Now you can begin with the physical installation of your APs.

• Install network and power connections You should install your network and power connections, such as Ethernet cabling or power line devices. Be sure to consult the installation guides.

• Mount APs Securely mount your APs to ensure that the general public cannot get their hands on them. Good mounting locations might be high on the wall or ceiling or above a drop-down ceiling.

• Connect the network and power cables After your network and power connections are in place and the APs are mounted, all you should have to do is connect the cables.