Pre-Deployment Preparation

---

The next step is to plan for the actual wireless deployment. When planning the deployment of a wireless LAN, you need to carefully assess and resolve risks. Otherwise unforeseen implications, such as RF interference, poor performance, and security holes will wreak havoc. By handling risks during the early phases of the deployment, you'll significantly increase the success of your new wireless network.

CHECK LIST FOR A SUCCESSFUL WLAN DEPLOYMENT

• Match the needs of the organization and end-users to the WLAN's final design.

• Identify the area the WLAN should cover to provide the optimal wireless/mobile activity.

• Measure radio characteristics of site.

• Survey and identify power options.

• Verify requirement of host connectivity.

• Survey existing network connections and existing equipment.

• Analyze results.

• Design the WLAN to provide optimal coverage for throughput and mobility.

• Design network as "legal" segment of any existing wired network.

• Be pedantic during the vendor selection process.

• Carefully plan integration into any existing network(s).

• Document equipment placement, power considerations, and wiring.

• Carefully plan for post-deployment needs, e.g. upgrades, network management and maintenance, user training and support, etc.

The Site Survey

With the assessment completed and the budget for at least a site survey in hand, the next step is to conduct a comprehensive site survey. Site surveys differ in their complexity and level of effort, based on technology and space.

Never deploy a WLAN without conducting a site survey. Even a small WLAN, serving only a limited number of end-users, should be deployed only after a site survey. And for larger WLAN systems a site survey is vital—unlike wired networks, WLANs have many variables and few fixed rules.

A site survey not only provides detailed specifications that address coverage, equipment placement, power considerations and wiring requirements, but it also gives the installers a realistic understanding of the wireless installation. A site survey also helps to determine whether a site has unusually high interference. Furthermore, it guides financial decision-making since it can be used to obtain accurate quotes from vendors, consultants, and installers. Without an effective understanding of your site's requirements, your wireless LAN installation will be more problematic, expensive, and time-consuming than necessary.

Note 

Every WLAN will have different goals and requirements so take your own organization's wireless connectivity needs into account when reading the following discussion.

Every WLAN design will be addressed differently. For example, one WLAN may need to provide for coverage that is isolated to a warehouse, and another will provide pervasive connectivity throughout a three-story office building, another will be set up to allow hotel guests to enjoy wireless Internet access.

PLANNING FOR GROWTH

Plan the initial installation with the future in mind. Requirements that need to be understood before beginning a site survey include:

• How many users will the WLAN support at the outset? Will there be user growth? If so, how much and when?

• Where are the potential users located? Where are the potential additional users located?

• What sort of applications will be run over the WLAN? You must plan your network layout so that data-rate "fall backs" do not interfere with the needs of more bandwidth intensive applications. For example, you may want to take advantage of zones with higher speed coverage to meet certain application requirements (e.g. the R&D department or the marketing department), while optimizing longer range coverage elsewhere. High data rate sites require a very thorough site survey.

• What types of computing devices are to be used by various user groups (PDAs, laptops, tablets, a mixture of both)? Is the make-up of these computing devices expected to change over time?

• If you use antennae to "reshape" rather than extend an AP's signal, beware that on top of their tricky installation, these antennae may or may not work with next generation technology.

The site survey either can be performed in-house using tools and equipment provided by wireless vendors, or it can be outsourced to an expert in site surveys. If this is an organization's first WLAN, outsourcing may be the preferable route, but later, as the WLAN is expanded to serve more end-users and to cover larger areas of the facility, inhouse resources can usually do the job.

The first phase of a site survey is research.

• Gather as much information about the site as possible. It is vital that you obtain a copy of the site's floor plans and/or layouts of all areas that the wireless network is expected to cover. These are the documents you will use to create a diagram of the coverage area.

• Test different access points by measuring each access point's signal strength. (Access point and antenna ranges differ by vendor specification.) Potential vendors should loan you the gear for these tests.

  SITE SURVEY CHECK LIST

  Make sure your site survey includes:

  • A detailed description of the desired coverage areas, along with a description of areas that do not need coverage.

  • A detailed layout of the coverage area. Use that as your site map. Consult facilities drawings, blueprints and wiring documents; a topographical map of the campus; an architect's floor plans; and anything that can show the location of host systems, power outlets, passageways, structural elements such as metal firebreaks and walls, and doorways. Make document copies so that you can mark them up.

  • A close estimate of the total number of WLAN users, descriptions of applications to be accessed through the WLAN, and data rates needed. This will help determine how to properly provision your collision domains through access point placement.

  • A set of the same brand and model of WLAN equipment that will eventually be deployed. (If possible, test more than one brand and/or model.)

  • Antennae. Consider trying out more than one kind of antenna (different antennae provide different performance ratios in different coverage areas). Understand that the actual pattern of an antenna can vary, and be careful of antenna polarity.

  • A portable battery pack or other method of powering access points as they are being tested.

  • Tie wraps, duct tape, or some other method for temporarily mounting access points and antennae.

  • Pictures (preferably digital). Use a camera to provide pictorial evidence of each step of the site survey. Such pictures will prove to be useful throughout the installation process.

  • A small wheeled cart with an UPS (uninterruptible/universal power supply) and extension cord at the bottom, and an extendable pole attached so you can mount an AP and antenna.

  • A small flashlight for seeing under ceiling tiles and the like.

• Note the location of such items as microwave ovens, cordless phones, satellite systems, RF lighting systems and neighboring WLANs—all can be sources of RF interference. Some or all of these items can seriously affect a WLAN's performance, depending on the item and the flavor of WLAN being deployed.

The Four Major Considerations

You are now at the phase where you can do a detailed examination of the site where the WLAN will be used. There are four major areas of consideration when designing a WLAN. They are:

1. Range and Coverage

2. Data Rate and Capacity

3. Interference Immunity

4. Connectivity and Power Requirements.

As you examine each of these areas to determine the WLAN's current needs, keep in mind possible future expansion needs. It will save a lot of headaches down the road. Let's now look at each area of consideration, individually.

Range and Coverage: Define the physical space and environment that the WLAN should encompass.

• Is it open field, in-building, or mixed?

• Does the WLAN coverage need to be isolated to only serve certain specific areas?

  SITE SURVEY TIPS

  • Since materials such as wooden floors can cause floor-to-floor interaction between access points, be sure that your channel selections are appropriate for vertically adjacent access points.

  • Concrete and steel rebar will bounce a signal, while single brick walls and sheetrock will allow for greater signal penetration.

  • Untreated windows will allow for greater penetration, while treated windows can (depending on treatment) cause tremendous problems. The same is true for HVAC ducting and elevator shafts.

  • Close all office and room doors before beginning the survey, in order to assess reception at its lowest, everyday level.

  • But also test the environment at its busiest. Water can absorb radio signals and, since the human body is 55 to 65 percent water, there can be a difference in range as people move about during the workday. Vehicle movement can also affect a signal's strength. If any radio signal's path crosses a parking lot, transportation area, or docking area, there can be a difference in the range during busy periods.

  • Consider redundancy for conference rooms (including spaces with multiple conference rooms in close proximity), cafeterias, and other multi-use spaces to ensure satisfactory throughput.

  • In high-security, limited-access areas, consider placing access points adjacent to or straddling the area.

• Since an access point's coverage area is typically spherical in shape, the size, shape, use and nature of the physical make-up (e.g. construction material, lighting, geographical features, etc.) of the coverage area will determine the number of access points that will be needed to provide adequate signal coverage.

Data Rate and Capacity: Next, determine the required data rate and capacity. Again, this data is essential in determining the number of access points needed for the WLAN to provide end-users with quality connectivity. This requires that you establish:

• How many users the WLAN is expected to serve at completion.

• What type of applications will they be running?

• What kind of computing devices will they use?

• Is it expected that there will be substantial changes over the next couple of years? If so, what are the changes and how will they occur?

Interference Immunity: Now it's time to assess potential sources of interference. This includes other WLANs, RF lighting, cordless phones, microwave devices, and satellite systems, etc., along with adjacent channel interferers as discussed in Chapter 10. A site survey will not only be used to determine how interference affects AP placement, but, in many cases, it may also be used to examine potential antenna performance patterns for antenna selection.

Connectivity and Power Requirements: Existing networking constraints often are overlooked during a site survey. For example, all of the organization's networks (wired and wireless) should be homogeneous. Care must be taken as to where the APs are placed, since many times they are installed in areas where there is no access to AC power or network cabling. But also review access point electrical installation alternatives that will prevent performance degradation from inherent or random electrical problems.

Now that you have catalogued your site considerations, you are ready for the actual survey. Mark all coverage areas on your site map. Next walk around the site and identify all possible obstructions for RF (e.g. freezers, coolers, X-ray rooms, elevators, etc.) marking their locations on the site map. Since metal is highly reflective for RF signals, collections of metal bookshelves and cabinets can constitute potential RF problem areas, so note their locations as possible obstructions. Also keep in mind that moving vehicles such as trucks, forklifts, and other equipment temporarily block signals. Therefore, if your site includes a docking bay, a busy transportation yard or a parking lot, conduct the survey when there is heavy activity in those areas.

Note 

Placing access points in very high locations (but not too high), or at opposite ends of the high traffic areas, can probably overcome the temporary blocked signal syndrome caused by activity in heavily trafficked areas.

Because of an access point's typical spherical coverage, the identification of areas where RF signals extend beyond the wireless network's intended coverage area is as important as identifying RF problem areas. Successful WLANs provide adequate coverage where needed, but take pains to minimize or eliminate coverage that extends beyond the organization's physical campus. Failing to limit RF coverage can expose the organization's network to unauthorized access.

Obstruction	Degree of Attenuation	Example
Open Space	None	Cafeteria, courtyard
Wood	Low	Inner wall, office partition, door, floor
Plaster	Low	Inner wall (old plaster lower than new plaster)
Synthetic Materials	Low	Office partition
Cinder block	Low	Inner wall, outer wall
Asbestos	Low	Ceiling
Glass	Low	Non-tinted window
Wire Mesh in Glass	Medium	Door, partition
Metal Tinted Glass	Medium	Tinted window
Human Body	Medium	Large group of people
Water	Medium	Damp wood, aquarium, organic inventory
Bricks	Medium	Inner wall, outer wall, floor
Marble	Medium	Inner wall, outer wall, floor
Ceramic (Metal Content or Backing)	High	Ceramic tile, ceiling, floor
Paper	High	Roll or stack of paper stock
Concrete	High	Floor, outer wall, support pillar
Bulletproof Glass	High	Security booth
Silvering	Very High	Mirror
Metal	Very High	Desk, office partition, reinforced concrete, elevator shaft, filing cabinet, sprinkler system, ventilator

Figure 8.1: Relative attenuation of RF Obstacles. The ability of radio waves to transmit and receive information, as well as the speed of transmission, is affected by the nature of any obstructions in the signal path. This table shows the relative degree of attenuation for common obstructions. Graphic Courtesy of Intel Corp.

To help ensure that the wireless network's coverage area does not extend beyond the physical campus, survey the area from "the outside in." Begin by placing an access point in the far outside corner of the proposed coverage area (position A in Fig. 8.2). Moving inward, locate the edge of your actual coverage area (position B) using the aforementioned survey methods.

Figure 8.2: Example of an "outside in" survey method. This method helps to ensure that the WLAN's coverage area doesn't extend needlessly beyond the physical plant. Graphic Courtesy of Cisco Systems, Inc.

Now move the access point to position B. Since position B represents the coverage edge when the access point was in position A, with the access point at position B, the reverse is true—position A is now the edge and it should be able to receive an adequate signal without RF spilling beyond the physical campus area. By performing another survey at position B, you can determine if your maximum coverage area includes more users than desired. If so, reduce the coverage area by using a smaller antenna or lowering the power level of the access point.

Surveying a site for the "weakest link" is another important activity. This requires consideration of different radio cards (i.e. wireless network interface cards), as well as knowledge of the computing devices themselves and how they house the transmitter/receiver. For example, surveying with a laptop with an exposed radio will not accurately indicate the coverage experienced by a traditional Automatic Identification and Data Collection (AIDC) terminal that reads barcodes and RF tags. The same holds true if the WLAN design calls for antenna diversity.

When the site survey is finished, provide a complete report to the deployment team, including the marked-up site map showing access point placement, and possible interference sources, along with cell structures, antenna choices, configuration parameters, power requirements, and photographs.

Professional Assistance

Site surveys are critical to a successful WLAN deployment. If not implemented correctly, the WLAN can end up costing more than just money and result in employee frustration and/or customer dissatisfaction. When planning the site survey, the in-house staff's knowledge and expertise with the technology and installation process must be considered.

A great deal of information can be obtained from a site survey, and while you may feel your in-house staff has the skills to perform the survey, they might not be able to adequately perform the necessary analysis. How the end product is analyzed is just as important as the survey itself. A good, informative analysis can support cell planning; cell search threshold; range and throughput; interference/delay spread; and bandwidth management for bandwidth-intensive applications, access point density, and load balancing.

To perform site surveys, vendors who cater to the enterprise market employ wireless experts, often engineers with many years of expertise. Using these specially trained professionals is like taking out a WLAN insurance policy. If the coverage isn't what was agreed to up front, the professional will come back and make it right (usually at no extra cost) because a reputable vendor will stand behind its expert's recommendations.

As mentioned previously, outsourcing to WLAN experts may be the wisest course, especially if it is the organization's first WLAN installation or if the WLAN is to serve a large organization or operate in a campus environment. Such assistance is available from wireless vendors and value-added resellers (VARs). Sometimes these wireless resellers charge a small fee for the site survey; sometimes the costs are the same as hiring an independent consultant, so shop around. An installation company or consultant can perform the site survey at a cost of approximately $1000 per day. The average survey will take a couple of days for a typical two- or three-story office building and close to a week for, say, a hospital or corporate campus.

Another source of expertise is an outside systems analyst who has worked with the organization's IT department in the past. The systems analyst can perform a series of on-site tests to help design and implement a wireless network. The survey determines the optimal number, placement, and configuration of access points and antennae for the required radio frequency (RF) coverage in a facility. Industry experts use tools to analyze frequencies, power capabilities, network loads, and coverage on the site. During this process, specifications are carefully developed for the required network layout and cabling, as well as for the necessary bridges, routers, and hubs.

Many environmental factors can disrupt WLAN coverage. Building construction materials such as paper, cardboard, and fabric absorb a lot of signal strength; whereas sheet rock and metal cause the signal to bounce around. And as previously mentioned, RF interference can come from a variety of sources. In such situations, an outside expert may be the best solution. Testing the proliferation of these frequencies, and knowing where to place access points and directional antennae, can eliminate these problems. Depending on the organization's needs, the expert can also consider data rates. End-users may have different data needs and may require more than one rate. Site surveyors will take those needs into consideration and recommend an appropriate solution.

Once all tests are completed, the outside expert prepares and presents a detailed report of findings and recommendations. After an internal assessment of needs and budget, the organization can move forward with the expert's wireless recommendations.

If the decision is to use a vendor's professional services or to hire a consultant, ask for references—particularly of customers that are in the organization's industry and with a similar facility. Use someone who has received certification from an independent organization such as a Certified Wireless Networking Professional (www.cwne.com). This holds true whether using a vendor's expert or hiring your own.

Note 

Some vendors offer RF Site Analysis training, which can be useful for any in-house personnel who might have the responsibility of conducting a site survey.

Site Survey Tools

A WLAN, while relatively inexpensive when compared with a wired network, a large WLAN is more complex and far more difficult to engineer than the conventional LAN design. Without good tools to help in the planning and deployment's troubleshooting process, the deployment team is operating blind. For example, rogue wireless devices and departmental systems can show up just about anywhere; a pilot WLAN that was not originally intended for production may still be in operation.

Experienced WLAN designers can walk into a facility, be it an office, warehouse or campus environment, give it a once-over and make educated guesses about how the system should be designed. But even they lean on site survey tools to ensure the final design is problem-free. For the average network manager, the site survey will be a trial and error process, and thus a good site survey tool will be invaluable.

Site survey tools are software that can be installed on a portable computing device to assist in the site survey process. This software establishes a two-way data network using both stationary and mobile devices at various points within the proposed radio coverage area. Once installed, these tools provide signal strength, throughput, best channel, and address information, which can be invaluable in making deployment decisions for the system.

Since site survey tools measure performance between access points and identify sources of interference, they help in determining effective operating range (i.e. coverage area) between end-users and access points, and in formulating optimal access point placement. For example, after placing the estimated number of APs in the locations you feel will provide the best coverage and overlap, verify the placements by walking around the WLAN's proposed coverage area with the site survey tool monitoring the signal levels of each AP. This allows you to verify the maximum distances that will maintain adequate signal levels (e.g. 4 or 6 Mbps). If a specific AP position doesn't provide the coverage needed, reposition the AP or add additional APs, and repeat the test.

Note 

Use site survey tools carefully. To give you an example, Intel reported that when one of its WLAN deployment teams was searching for other wireless devices on an IP address range that was fairly large (meaning the process involved probing every address within a specific range for information), the probed addresses ran through the server farm in Intel's CIS department, setting off alarms. The IT center's administrator, convinced that a major hacker attack was under way, later discovered that Intel was just testing to see whether its large SP2 data center had hidden wireless network ports. So unless you want to test the efficacy of some of the IT administrator's blood pressure medication, the author (and Intel) recommend carefully limiting the IP range on discovery probes.

Vendor-provided Tools. Most vendors include simple site survey tools with their wireless card and AP installation disks, although features vary greatly. For example, you can find vendor-provided survey tools that measure signal strength and quality, data rate, or a host of other relevant information about a WLAN's performance and efficiency. All of Cisco's wireless client adapters include the Cisco Aironet Client Utility (ACU) that helps in the configuration, monitoring, and management of the adapter. The site survey functions also produce easy-to-understand, detailed graphical information, including signal strength, to assist in the correct placement of APs. Moreover, the ACU also provides signal-to-noise ratio measured in decibels (dB), and signal level and noise level measured in decibels per milliwatt (dBm).

The survey tools that come with the today's APs are generally web- or command line-based, and provide the ability to configure APs individually. Vendor-provided survey tools vary widely in functionality and usability. In the author's view, the only site survey functions shared by most vendor-provided tools are displays showing the strength and quality of the signal emanating from the AP. Fortunately, the tools available from most enterprise-oriented vendors have improved significantly over the past several years and are expected to continue to improve. Industry experts expect that by 2004, most major wireless LAN vendors will offer a comprehensive suite of products (primarily software) focused on site surveying and RF troubleshooting.

Advanced Site Survey Tools. Some WLAN deployment teams may feel that the site survey tools provided by the vendor are insufficient for their needs. In that case, you might want to look into advance site survey tools. A spectrum analysis tool can provide the "eyes" and "ears" for a deployment team to understand the affects of the environment on the transmission of 802.11 signals. Some tools can graphically illustrate the amplitude of all signals falling within a chosen 22 MHz channel, enabling the deployment team to distinguish 802.11 signals from other RF sources that may cause interference. Thus the team can locate and eliminate the source of interference, or use additional access points to resolve the problem.

Another key spectrum analysis feature that a deployment team might find useful is the ability to monitor channel usage and overlap. For example, 802.11b accommodates only three access points in the same general area; if there are more, the APs experience interference and corresponding performance problems. This limitation creates difficulties when planning the location and assignment of channels in large networks. Advanced site survey tools can display these channels, enabling the team to make better decisions on locating and assigning channels to access points.

Many may question if the value of advanced survey tools is worth the expense. Others understand that such tools not only help them to spot potential design flaws, but also can help to avoid serious problems down the line. Due to the high cost of these advanced tools, you should only consider them if you are designing multiple WLANs or a WLAN whose environment is complex, e.g. warehouses with lots of high metal racks, manufacturing plants full of machinery, a large campus—any of these WLAN designs easily warrant the additional costs of using advanced tools. If you want to investigate the possibility of procuring advanced site survey tools, consider those offered by such companies as AirMagnet, Berkeley Varitronics Systems, and Fluke Networks.

Once the WLAN is up and running, these same tools can be used to monitor the installed access points' signal strength to (1) ensure they are providing adequate cover, and (2) to identify failure zones.

Note 

You also might want to check out a freeware product—Netstumbler (www.netstumbler.com)—in many cases this tool is far superior to the site survey tools the wireless equipment vendors provide. Network Stumbler not only captures signal strength and signal-to-noise statistics, but even more importantly, it helps network administrators identify and locate rogue access points, including any WLAN that an employee or group of employees may have installed without the IT department's permission.

---