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CH A P T E R8Site Survey and RF Design ValidationSite Survey IntroductionIn the realm of wireless networking, careful planning is essential to ensure that your wireless networkperforms in a manner that is consistent with Cisco’s design and deployment best practices. With that inmind, we cannot stress enough how important it is to perform a thorough site survey before and after theCisco Unified Wireless deployment. A pre-site survey allows the systems engineer to assessrequirements and design the network in manner that promotes and encourages scalability while alsomeeting expectations with regard to the applications the network will support.Through our experiences, our TAC and Escalation Teams have discovered that many of our customersand even partners perform the site survey incorrectly or skip the site survey altogether. In almost 70% ofCisco wireless deployments, our Wireless Escalation Team and Advanced Services are called in toperform remediation for customers due to deviations from documented design and deployment bestpractices as they pertain to RF Design. In some cases, it is a matter of experience, and in others it isrelated to improper planning.As we explore the possibilities, we have also determined that a majority of the environments weresurveyed for data, but not for voice. When executives and IT managers think about purchasing solutions,they often consider buying equipment that will provide a good return on their investment. With that inmind, a wireless network that is going to be deployed throughout the enterprise should be designed anddeployed for voice to ensure that it is scalable and that user mobility is enhanced.NoteWhile one organization might have a certain set of criteria for their wireless deployment, it is of vitalimportance to ensure that your company employs a Certified Cisco partner that has their AdvancedWLAN specialization and also has a reputable background with regard to performing pre- and post-sitesurveys.For the purposes of this troubleshooting guide, we will assume that the wireless network has alreadybeen deployed. Based on this, we will focus on what tools can be used to isolate RF-related problems,such as excessive retransmissions, RF multipath, and co-channel interference, and we will discuss topicsand tools related to performing a post audit along with RF analysis of the existing wireless network.Since the focus of this document will be on troubleshooting, we will discuss the basics of performing apost-site survey as it pertains to the proper deployment of a VoWLAN.Voice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-1

Chapter 8Site Survey and RF Design ValidationPerforming a Post Site Survey AssessmentPerforming a Post Site Survey AssessmentThe need for a wireless site survey is different in every situation. Performing a post assessment of theenvironment is very similar to a pre-site survey. There are particular guidelines and criteria that need tobe met. Once a systems engineer has determined that VoWLAN users are being subjected to audioproblems due to inadequate signal, interference, or other RF-related problems, performing a post surveyof the environment becomes crucial from a troubleshooting perspective.Environmental CharacteristicsWhen preparing to perform a post analysis of the environment, be certain to consider the environmentalcharacteristics of the building or site where the wireless network was deployed. A large building withseveral floors may require only a minimal amount of time, especially if each floor has a similar physicalblue print, however, it is important to evaluate every floor individually. An environment such as an oceanliner may vary completely from deck to deck and will prevent you from using a cookie cutter approach.The following are elements that you should consider when performing a post assessment of theenvironment.1.Review requirements: For VoWLAN deployments, it is crucial to understand what the transmitpower of the client device is to ensure that access points and VoWLAN handsets transmit at the samepower. This will mitigate problems such as one-way audio.2.Wireless tools: When performing the post assessment, it is also recommended that you use wirelesstools such as Cisco Spectrum Expert, Wireshark, Omnipeek, and AirMagnet to the isolate root causeof RF-related problems.3.Obtain building and floor blue prints: WCS is a great place to start your evaluation. Remember,while WCS will show you the physical layout of a building, WCS should not be used as a primarytool for performing a post wireless audit.4.Inspect the environment: As you are troubleshooting a problem-related RF propagation or a lackthereof, it is important to perform a physical walk-through of the environment and take into accountwhere the access points have been placed, what types of antennas are in use, the height of the accesspoints, and the direction of each antenna as it relates to the respective coverage area.5.Evaluate the LAN: When performing a post audit, evaluation of the wired infrastructure isimportant for several reasons. First and foremost, you want to ensure that the physical LAN cansustain the appropriate level of throughput without QoS. This will ensure that voice traffic can laterbe assigned to queues or marked with a level of QoS that facilitates greater priority as voice traffictraverses the infrastructure. Once you have validated the physical topology, you can then trustpackets according to DSCP or CoS and ensure that voice packets traverse the wired and wirelessLAN with the appropriate level of QoS.6.Identify sources of RF interference: This is probably the most important aspect of a post auditwhen deploying 802.11a/b/g/n solutions on the 2.4 and 5 GHz bands. Often there are severaldifferent types of interferers. The most common of these are from commercial grade microwaveovens, blue tooth devices, and cordless phones that operate on the 2.4 GHz frequency band. Themost common tool used by wireless engineers at Cisco is Cisco Spectrum Expert. Spectrum Expertis an analysis tool that can used to locate and isolate sources of interference and identify aboveaverage channel utilization after the initial deployment. Refer to the section “RF Design Validation”for channel utilization recommendations.7.Analyze and define the cell edge: This requires the use of AirMagnet Survey, although there aresimple tools like Omnipeek or Wireshark that can be used to measure wireless traffic as a clientroams from one AP to another. According to design best practices that revolve around the Cell EdgeVoice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-2

Chapter 8Site Survey and RF Design ValidationVoWLAN RF Design ValidationDesign, a wireless handset should roam before the RSSI reaches -67 dBm. You can analyze signalstrength and determine the approximate cell edge by measuring the signal strength in a beacon frameas you move from the center of one cell towards the edge of that cell.8.Validate antenna usage and AP placement: As it pertains to RF design and deployment bestpractices, we suggest performing advanced wireless in an effort to understand how RF propagateswith the existing environment.9.Post-Site Survey Report: The wireless post audit report should contain detailed facts about theexisting deployment and outline deviations in design and deployment best practices. The purpose ofthis report should be to provide systems engineers with enough information to successfullyremediate the existing deployment to ensure proper functionality, high availability, and seamlessuser mobility with minimal delay and jitter.VoWLAN RF Design ValidationTroubleshooting Radio Frequency DesignThe most important aspect of any VoWLAN is user mobility. Systems Engineers need to ensure that theexisting WLAN will facilitate user needs, while also ensuring that users have seamless connectivitywhile moving throughout their enterprise. Voice has stringent requirements with regard to RadioFrequency Design, and understanding RF propagation and VoWLAN design and deployment bestpractices is essential for successful voice over wireless LAN deployments.When troubleshooting a VoWLAN specifically, it is important to understand how packet loss and jitterwill affect voice quality. Specifically, Cisco references a principle referred to as Cell Edge Design whendeploying access points and antennas. Deploying the VoWLAN according to this design principle willensure that your VoWLAN is highly available so that users can move seamlessly throughout the network.When troubleshooting issues that pertain to a lack of RF coverage, interference, or issues that might berelated to user mobility, it is important to understand the following design fundamentals as they relateto the Cell Edges Design principle, channel utilization, noise, retransmissions, and overall packet lossand delay.RF Design Validation1.The optimal VoWLAN Cell Edge recommendation is -67 dBm.2.An optimal VoWLAN deployment will require at least a 20 percent cell overlap for 2.4 GHz and15-20 percent for 5 GHz for access points that reside on different channels.3.Over all Channel Utilization should be less than 50 percent.4.The Noise floor should not exceed -92 dBm, which facilitates a Signal to Noise Ratio of 25 dB.5.Retransmissions should be kept under 20 percent.6.Packet Loss should remain under 1 percent and jitter should be kept to less than 100 ms.Cisco Enterprise Mobility Design Guide prise/Mobility/emob41dg/emob41dg-wrapper.htmlVoice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-3

Chapter 8Site Survey and RF Design ValidationSite Survey ToolsVoice over Wireless LAN 4.1 Design oteIf you are troubleshooting and you determine that the VoWLAN does not adhere to the outlinedrequirements above, we strongly encourage you to perform a post site survey and assess the existing RFDesign. The following section should provide you with sufficient information to analyze the RFenvironment and remediate the wireless deployment until the RF design meets the appropriate criteria.Site Survey ToolsIn most cases, we hope that a pre- and post-site survey have already been performed before deployingthe Cisco Unified Wireless Network for Voice. In a situation where it has not been performed, a postaudit of the environment is essential to understand the existing RF design and to remediate the networkuntil it is accordance with Cisco’s Design and Deployment best practices for VoWLAN deployments.AirMagnet Survey and VoFi AnalyzerAirMagnet Survey and AirMagnet VoFi Analyzer are primary solutions used by the Cisco Escalation andAdvanced Services Teams for managing, remediating, and optimizing a Cisco Unified VoWLAN.AirMagnet Surveyor itself provides information related to RF propagation within the physicalenvironment. AirMagnet Survey also has preconfigured profiles for the Cisco 792xG Series wireless IPphone that allow Survey to predict RF propagation and to validate and plot the phone call performance,call capacity, RF coverage and roaming behavior at every location on a floor map. This eventually leadsto root cause analysis with regard to poor call performance.In Figure 8-1, we show a post assessment where a systems engineer walked an area where a VoWLANissue was being experienced. As you can see in the following figure, Figure 8-2, the screen shot displaysthe information for those access points and the signal strength for each area that was assessed using thesurvey utility.Voice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-4

Chapter 8Site Survey and RF Design ValidationSite Survey ToolsFigure 8-1Walk-ThroughFigure 8-2Signal Strength for Given AreaVoice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-5

Chapter 8Site Survey and RF Design ValidationSite Survey ToolsNoteWhile WCS can be used for planning, location tracking, and RF visualization, the heat maps in WCS arepredictive based on the antenna type, antenna direction and power levels configured on the WirelessLAN Controller. WCS should not be used as a pre- or post-site survey tool by any means.With regard to the VoWLAN and the RTP stream between the AP and 792xG Series wireless IP phone,a poor or unreliable RTP stream can have any number of potential problems. It may be an issue with the792xG Series firmware specifically, the RF environment, a misconfiguration, a QoS marking over theair, or even problems over an IP-PBX or H.323 gateway. Due to the level of complexity, VoWLANtroubleshooting can become particularly challenging and time-consuming to diagnose.AirMagnet also has a Wi-Fi Analyzer and VoFi Analyzer which have the ability to display your networkin terms of calls and call quality. VoFi Analyzer works in the same manner as a protocol analyzer andhas the ability to score every RTP stream in terms of WiR-Value and a WiMOS score based on packetmetrics, such as loss rate and jitter.As you can see in Figure 8-3, each call is color-coded according to call quality. The VoFi Analyzerdisplays streams that experience problems.Figure 8-3VoFi Pro AnalyzerThe AirWise analysis engine in VoFi Analyzer also has the ability to detect common problems withinthe VoWLAN such as choppy audio, one-way audio, and no audio, and provides easy-to-understand databased on configurable alarms.Voice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-6

Chapter 8Site Survey and RF Design ValidationSite Survey ToolsIn addition to troubleshooting call streams from an RF perspective, the VoFi Pro Analyzer can be usedto receive syslog data directly from the Cisco 792xG Series wireless IP phone. This is ideal whentroubleshooting issues related to excessive roaming due to RSSI differential seen by the handset or RFrelated problems such as multi-path.Detailed information about the AirMagnet suite of products can be found at the following location:http://www.airmagnet.com/Cisco Spectrum ExpertCisco Spectrum Expert Wi-Fi integrates with the Cisco Unified Wireless Network to deliver real-timespectrum intelligence data. Cisco Spectrum Expert has the ability to detect, classify, and locate sourcesof RF interference in the unlicensed 2.4-GHz and 5-GHz bands.WCS and Spectrum IntelligenceWhile Cisco Spectrum Expert can be used as a separate tool, the Cisco Wireless Control System (WCS)also works in conjunction with Cisco Spectrum Expert to provide visibility into interference sources thatmay cause wireless performance degradation. With Cisco Spectrum Expert Wi-Fi, the source of theinterference can be determined, allowing businesses to remove, move, shield, adjust, or replace thesource of interference.The WCS and Cisco Spectrum Expert Wi-Fi is part of the Cisco’s Spectrum Intelligence solution andintegrates with the Cisco Unified Wireless Network to monitor the wireless network.To implement and utilize this for troubleshooting, systems engineers need to adhere to the followingcriteria. Cisco Spectrum Expert Wi-Fi Cisco Wireless Control System (Software Release 4.2 or later) Cisco WCS Spectrum Intelligence licenseVoice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-7

Chapter 8Site Survey ToolsWCS and Cisco Spectrum IntelligenceFigure 8-4WCS and Cisco Spectrum IntelligenceVoice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-8Site Survey and RF Design Validation

Chapter 8Site Survey and RF Design ValidationSite Survey ToolsFigure 8-5Wireless Control SystemWireless SnifferWireshark or OmnipeekOnce you have isolated and remediated the RF problems, refer to the sections on GeneralTroubleshooting and using Omnipeek for instructions on how to take wireless sniffer traces to analyzea VoWLAN.NoteWith regard to following VoWLAN design and deployment best practices, Cisco does not support asame-channel design as used in some Distributed Antenna System (DAS) deployments. A VoWLANdesign must include a minimum of the three non-overlapping channels that are consistent with the802.11 specifications for 2.4 GHz and 5 GHz.Voice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-9

Chapter 8Site Survey and RF Design ValidationSite Survey ToolsNoteThe Coverage Hole Algorithm is a mechanism built into Radio Resource Management (RRM) that willincrease the transmit power of an AP to ensure the appropriate amount of coverage once a certain numberof clients roam into the coverage hole (three or more clients by default). While this is a feature, it isimportant to implement bandwidth throttling on the controller for the 2.4 GHz band. Throttling thetransmit power of the AP will ensure that asymmetric transmit does not occur, leading to one-way audio.DTPC is another mechanism that can potentially remedy this issue as well.Voice Over Wireless LAN (VoWLAN) Troubleshooting Guide8-10

Chapter 8 Site Survey and RF Design Validation Performing a Post Site Survey Assessment Performing a Post Site Survey Assessment The need for a wireless site survey is different in every situation. Performing a post assessment of the environment is very similar to a pre-site survey. There are particular guidelines and criteria that need to be met.File Size: 4MBPage Count: 10Explore further3 types of wireless site surveys and how to conduct themwww.techtarget.comThe 6-Point Checklist for a Wireless Site Surveytradeshowinternet.comSite Survey Guidelines for WLAN Deployment - Ciscowww.cisco.comWLAN Network Planning and Site Surveyd24wuq6o951i2g.cloudfront.netWireless Site Surveys: The Basics - Network Computingwww.networkcomputing.comRecommended to you b