Deployment Guide: Higher Education Technical Guide Site Survey 061808 2 Site Survey Guide Table of Contents Introduction .................................................................................................................................3 Types of Site Surveys ....................................................................................................................3 Survey Requirements....................................................................................................................5 Equipment Required.....................................................................................................................7 Performing the Survey..................................................................................................................8 Getting Started .............................................................................................................................9 Summary .................................................................................................................................... 11 Wi‐Fi Tools.................................................................................................................................. 11 100508 2 Site Survey Guide Introduction The purpose of this guide is to serve as an introduction and education on the basics, the values, and best practices associated with performing Wi‐Fi site surveys. We will describe the process Xirrus uses for site surveys and demonstrate how these same processes can be used by anyone with readily available tools. Poorly performed site surveys can result in not only coverage gaps and reduced performance, but also increased costs associated with identifying and resolving these issues after the fact. The goal of any site survey is to determine the number and location of access points (APs) required to meet wireless design goals (such as coverage, performance and user capacity). Getting the site survey accurate is just as important as selecting the proper hardware. If the site survey is too optimistic and calls for too few access points, the final installation will yield poor coverage and/or performance. This in turn will require a follow‐up survey to determine what changes may be required to the number or location of deployed APs. The end result will be increased costs not only in additional APs, but also the associated costs of pulling cable, equipment, contractors, and installation effort. Conversely, if the survey is too conservative, more access points than are needed will be specified and again money is wasted on unneeded equipment and labor charges. Types of Site Surveys Active vs. Predictive There are two primary methods in which site surveys can be performed: Active and Predictive. Active site surveys, also called live surveys use an actively transmitting access point and a Wi‐Fi enabled laptop or other tool to measure Wi‐Fi signal strength in the actual environment to determine how many and where access points are required. Predictive site surveys use software packages to emulate the environment. Floor plans of the site are imported and allow the user to assign attenuation values (how much RF energy is absorbed) for each wall and object in the building (most tools typically have a database of materials to choose from), the application will then predict the number and location of access points required to meet the desired coverage and performance goals. Active site surveys – measures the real performance of each access point location and innately takes into account the physical characteristics and contents of the building. There is no need to estimate the density of the walls or floors. An active site survey is also able to detect any sources of interference and apply this information to determine SNR (signal to noise ratio). This type of survey not only provides the most accurate performance information for each access point, it also allows for the physical inspection of the site to assure the access point can be mounted in the selected location. The downside of this type of survey is it is labor intensive, requires physical access to the building and demands a higher level of RF knowledge to perform. Predictive site surveys – may take less time but still require “seat time” in front of a computer program versus the “leg time” needed for an active survey. As the name implies the software performs a predictive analysis of the building, once floor plans are imported it uses industry defined attenuation values for walls, 100508 3 Site Survey Guide doors, windows, etc. The difficulty here is the common GIGO (Garbage In‐Garbage out) problem associated with trying to accurately model the contents and makeup of the building (especially ones that have changed or remodeled over time). Survey Comparison Active (live) Survey Predictive Survey Survey Effort Higher Potentially Lower Access Point Placement Exact Locations chosen Final locations still need be chosen Wireless Coverage Measured / Known Predictive: May require more APs Wireless Performance Measured / Known Estimated: May require more APs Cabling and Equipment Typically Accurate May require cables to be added or moved Installation Simplified May require moving APs or adding more APs Remote vs. On‐Site Survey Although the following discussion goes hand in hand with Active vs. Predictive surveys, it is important to identify the additional value beyond RF analysis of an on‐site active survey vs. a predictive software analysis. The key point is to understand the value of walking the facility as the survey is performed and knowing what to look for. The active survey not only provides the most accurate performance information for each access point, it also allows for the physical inspection of the site to assure the access point can be mounted in the selected location. If AP placement is based just on the marking on a floor plan the actual installers may find the location unacceptable for installation, as it may not be physically mountable at the predicted location. A physical walkthrough of the installation site enables identification and addressing of the following types of issues before installation day, where delays can be costly: Identifying AP locations – This is will greatly assist those pulling data/power cabling and avoid costly changes. Physical restrictions – Are there mounting issues that prevent an AP being installed where it would best be located, such as lighting, air conditioning ducts, sprinklers, appropriate mounting points, etc. It also allows installers to identify all tools and any special mounting hardware required for the install. RF Interference issues – Are there nearby non‐802.11 devices that emit RF energy (microwave ovens, medical equipment, air conditioning units, etc.) that may interfere with the proper operation of the AP? In addition, what other Wi‐Fi networks are located in the environment? If other 5 GHz networks are nearby 100508 4 Site Survey Guide there is typically sufficient available channels to avoid interference, however with 2.4 Ghz (11b/g) there are only 3 usable channels and a nearby network also using these could result in interference. At this point there should be some discussion between IT staffs to set channels and power to avoid interference that could degrade both networks performance. Aesthetic Issues – Are there corporate policies that restrict the location, color, shape, etc., of the Access Point. Regulations/Codes/Policies – Are their specific rules that the deployment must confirm to, such as AC power distribution, cabling runs, RF power limits, plenum rating, or other issues. Arriving on site with inappropriate components can add expensive delays. Flexibility of environment – Many environments ‐ especially schools, conference centers, warehouses, manufacturing facilities – can be very physically dynamic. From one day to the next, walls can be moved, equipment shuffled, racks rearranged, etc. A visual walkthrough and on‐site discussion can identify and address these issues prior to the install and avoid post install complications. Bottom line – A predictive survey is often easier to accomplish but has the potential to make the actual install more complex due to unknowns that could be encountered. An active site survey that includes a physical walkthrough is more complex, however will make the install go smoother by identifying potential issues up front and ultimately result in a more successful deployment. Survey Requirements Before starting a site survey, it is of critical importance to define the purpose of the survey. It may seem very basic to include this as a requirement, however it is amazing how many surveys are conducted with the focus only on RF coverage and no consideration given to the reasons for installing Wi‐Fi in the first place. The following components should be considered before selecting a vendor or performing a survey as they will help determine the product and survey requirements. Business Requirements – What is the purpose of adding/upgrading the Wi‐Fi services? Is the goal to just add Wi‐Fi hotspots, connectivity in the conference rooms, or is it a building/campus‐wide pervasive Wi‐Fi service that provides seamless coverage and roaming throughout the enterprise. The answer to this question will help determine the vendors, products and Wi‐Fi architecture you select. Application Requirements – Bandwidth and QoS capabilities define the products purchased, however minimum RF signal strength must also be considered for voice over Wi‐Fi solutions. The majority of Wi‐Fi phone vendors require a ‐68 dBm RSSI (received signal strength indicator) or stronger signal. Surveying to this level avoids having to re‐survey and add APs/cabling at a later time. Security Requirements – Another topic often overlooked during a site survey is security. Controlling the amount of RF energy transmitted beyond the enterprise boundaries (parking lots, etc.) should always be a consideration. With proper AP placement, power levels, and use of directional antennas, RF leakage can be minimized. To clearly define the edge of RF coverage, vary power levels and record signal strength readings on inside and outside walls of facility. Directional antenna can also be used for RF shaping. 100508 5 Site Survey Guide Coverage vs. Capacity – Most vendors offer separate survey procedures for coverage or capacity models. Coverage surveys are designed to generate a solution with the minimum number of APs to guarantee client association. Capacity surveys are designed to support larger numbers of stations and offer higher data rates to clients; these typically group more APs in a single area, resulting in smaller cells and with more radio choices for clients. The result is typically stronger signal strength connections for clients, which results in higher data rates. Cell Size Planning‐ Wi‐Fi in the 5GHz band (802.11a/n) has slightly smaller cells than Wi‐Fi in the 2.4GHz band (802.11b/g/n). Design for 5GHz and it will pretty much ensure coverage for all 802.11a/b/g/n clients. Larger cells sizes can reduce number of APs required, but could result in client connectivity problems. Choosing Between 2.4 GHz or 5 GHz – Both bands are commonly deployed in Wi‐Fi networks today and it is strongly recommended to perform the survey for both bands. Wireless Bridging (WDS) Requirements – Will AP to AP wireless bridging be used? This question may come up in outdoor deployments, in warehouses where intra‐AP distances could exceed 100 meters or even building‐to‐building links. As part of the survey, examine point‐to‐point path loss. Special attention should be paid to any trees or foliage in the path as seasonal growth could impact the link. Wired Infrastructure – Don’t overlook the existing wired infrastructure, as its capabilities or lack thereof can severely impact Wi‐Fi performance. For example if deploying 802.11n Wi‐Fi, the uplinks will require Gigabit links. Verify the cable plant and switches are capable of Gigabit Ethernet or if a wired network upgrade will be required. In addition, verify AP powering options. If PoE will be used, verify that new or existing PoE products provide sufficient power (802.3af, 802.3at, or other) for the Wi‐Fi to be deployed (for example 802.11n requires increased power). The 802.11n Site Survey – The introduction of 802.11n has added some confusion and caveats to the traditional site survey. 802.11n is not about higher transmit power, but about better receiver sensitivity (ability to listen). 802.11n range improvements require 11n radios at both ends of the connection ‐ the station and Access Point. The majority of networks deployments will include a mix of client types (802.11n and non‐802.11n) and cell sizes should therefore remain the same. Some recommendations for performing 11n surveys include: • Always survey for both 2.4/5 Ghz‐ This is the same as for 802.11a/b/g surveys and is recommended so both bands will be properly supported • Use an 802.11abg adapter for site survey – This is recommended even for 11n APs as support for legacy 802.11a/b/g devices will continue for some time • Use an 802.11abgn adapter only if all network devices will be 11n capable – Although some networks may meet this criteria, the vast majority of Wi‐Fi networks will be mixed 11a/b/g/n environments for some time 100508 6 Site Survey Guide Equipment Required This section identifies specific equipment, tools, and software Xirrus recommends for performing a professional quality site survey. Array/APs/Radios: Use the type of Array or AP to be deployed. All surveys should be performed using products identical to those that will be installed; this approach helps to guarantee installed coverage matches that of the survey. Using different products for survey and production could result in significant variability in actual coverage. Support Equipment: • • • • • Multiple copies of the floor plan should be available to track mounting locations, record obstructions, and indicate mounting options and general note taking. Surveys should be conducted with Arrays/APs located as close as possible to where they will be installed. Xirrus uses tripods to locate Arrays. If using standard APs, it is recommend to pole mount them for easier placement. General purpose equipment such as AC extension cords, Ethernet cabling, console cables, ladders, flashlights, etc, should be available to assist on the survey. A camera is desirable to record unique mounting obstacles so appropriate mounts can be defined. Some form of location identifiers (e.g. stickers) to indicate where Array/APs will be placed. Software/Firmware Tools A laptop with the following tools will be required for the survey: • RF survey tool, for example AirMagnet Survey or similar. Alternatively for more simple surveys, free tools that read Wi‐Fi signal strength can be used. The Xirrus Wi‐Fi Monitor gadget is a free tool that can be used and is available at http://www.xirrus.com/library/wifitools.php. • Optionally some form of RF monitoring tool that will identify nearby APs and perform Spectrum Analysis to identify potential noise sources. The Xirrus Wi‐Fi Array has these capabilities built‐in and can be leveraged during the survey process. 100508 7 Site Survey Guide Performing the Survey This section describes procedures used by Xirrus to perform a site survey. Using this methodology and readily available Wi‐Fi tools, an IT administrator with a moderate degree of Wi‐Fi knowledge can perform a reasonably accurate survey of their own. As previously discussed, the site survey is one of the most crucial steps in a successful Wi‐Fi network deployment. With many techniques commonly used for Wi‐Fi site surveys and the many modes of 802.11a/b/g/n, ensuring the survey is done right is more important than ever. A poorly performed site survey does not only impact you network today, it can result in a costly redesign when it’s time to upgrade to 802.11n. Components of a professional site survey performed by vendor‐qualified individuals should include: • Complete on‐site survey of all areas to be covered, using same products that will be deployed. • On‐site RF spectrum analysis to identify potential interference issues. • Post survey analysis and report including coverage maps and RSSI values. • Post install survey to confirm installed Wi‐Fi equipment meets proposal requirements. Recommended Site Survey Parameters • • • Signal Strength ‐70dBm RSSI (or stronger) in all areas to support full data rates Signal Strength ‐68dBm RSSI (or stronger) in all areas to support Wi‐Fi voice handsets Client should be able to see at least 2‐3 radios at every location these signal levels Before Arriving On-site • • • Discuss business requirements with all who have a stake in the Wi‐Fi solution Obtain digital floor plans of facility to be covered (e.g. .jpg, .bmp, .png) Ensure access will be available on the day of the survey to all area, or a representative subset of area, that is to be covered by Wi‐Fi Tips Before Starting This section includes a number of tips and recommendations to help ensure a successful and accurate survey. • It is a good idea to deploy as many Arrays as reasonable, as this will simplify the survey process and provide superior survey measurements vs. just using just one Array and continually moving and taking measurements. • Set up Tripod/Array in such a way that it correctly represents how the Array will be mounted • For each Array and Array location during the survey, use a separate SSID so specific coverage of each Array can be easily distinguished. • Set Array beacon rate to 20ms ‐ this enables the survey software to receive many more beacons. After the survey, don’t forget to reset beacon rate to default. • Perform surveys under worst‐case usage conditions for the environment, for example doors closed, curtains drawn, etc. • Be aware that each client (laptop/Wi‐Fi card/driver) will have slightly different readings. This is a good reason to be conservative when performing Wi‐Fi surveys. 100508 8 Site Survey Guide • • • • • • • • Perform the survey at both 5GHz and 2.4GHz. Do not survey for 802.11n only unless you are 100% sure no legacy (802.11a/b/g) clients will be supported (not common) Take measurements where users will be located: desks, tables, etc. Take multiple readings in each room Consider additional signal attenuation if Arrays/APs will be placed in enclosures or above ceilings. In multi‐floor building, check for floor‐to‐floor bleed‐through. If significant, plan for coverage of areas from Arrays/APs placed above/below a given floor. Stagger the final placements of the Arrays/APs between floors to account for this. Constantly consider installation concerns when surveying and prepare accordingly Don’t rush! Getting Started This section demonstrates a process that Xirrus has found to be successful and accurate. 1. Start with laptop in a far corner of the facility and the Array/AP placed nearby. Move the Array/AP away from the laptop until signal strength drops to, but not under, the specified RSSI value (e.g. ‐70) 100508 9 Site Survey Guide 2. Find the other edge of coverage area by moving the laptop away from the Array/AP and surveying until the signal strength drops to, but not below, the specified signal strength values. 3. This defines the coverage area for the single Array; identify the location by recording the information on a floor plan and also with some form of physical tagging (e.g. stickers on the ceiling) to identify the exact location where the Array will be located. 4. Continue to repeat this process as you move across the building until the complete facility has been surveyed. If surveying a multi‐story facility, make sure to verify floor‐to‐floor coverage before turning moving the Array. 5. Use the Array’s RF Monitor/Intrusion Detection function (or similar tool) to find other APs in the area. All detected APs should be identified as known or unknown devices and considered in the overall survey. 6. Use the Array’s RF Monitor/Spectrum Analyzer function (or similar tool) to identify sources of interference, either 802.11 co‐channel interference or non‐802.11 noise. Once a noise source is identified, define a plan for interference avoidance. In some cases, discussions with neighboring Wi‐ 100508 10 Site Survey Guide Fi networks IT staff should be set up to arrange for channel planning and power setting coordination. 7. Finally, share complete survey information with all stakeholders. Discuss covered areas, RSSI values, weak spots and indicate how many radios are available to mobile users throughout the facility. This last part is key as we recommend at least 2‐3 strong radios to all clients to provide resiliency and to reduce the possibility of a single radio failure taking down any area. Example of ‘Active’ Site Survey results (using AirMagnet tool) Summary Predictive site surveys may be acceptable in some less complex Wi‐Fi deployments, however the larger and more business critical your Wi‐Fi project is, the more essential an active site survey becomes. Rolling out Wi‐ Fi for a large office building or campus environment mandates an accurate site survey. With large projects, even being off by a small percentage could result in unacceptable additional costs associated with additional equipment, cabling, and manpower requirements. An active, on‐site survey using tried and true best practice methodologies is the most accurate type of survey and Xirrus strongly recommends it be made a requirement of any Wi‐Fi deployment. Final Thought ‐ You are betting the success of your Wi‐Fi network on the survey, and maybe your job! Wi-Fi Tools • • Wi-Fi Basics FAQ – www.xirrus.com/library/faq.php o Useful Wi-Fi FAQ for understanding the components, requirements and goals associated with performing a site survey Wi-Fi Tools – www.xirrus.com/library/wifitools.php Xirrus has assembled several useful Wi‐Fi tools found to be of great value in planning, deploying, and managing Wi‐Fi networks. Xirrus Wi-Fi Reference Posters – www.xirrus.com/posters o Educational/reference information on Wi-Fi o • 100508 11 Site Survey Guide • Xirrus Wi-Fi Widgets/Gadgets – www.xirrus.com/library/wifitools.php o The Xirrus Wi-Fi Monitor provides detailed information about surrounding Wi-Fi networks and your laptop’s current Wi-Fi connection, including SSID, signal strength, IP address, MAC address, security level, vendor, and network type. This free tool can be used to perform simple site surveys. 100508 12 Guide