Transcription

Best Practices for High DensityWireless Network DesignIn Education andSmall/Medium BusinessesWhite Paper

Table of ContentsExecutive Summary Introduction Determining Access Point Throughput Establishing Bandwidth Requirements TOP 10 High Density Design Recommendations Conclusion About NETGEAR/Debra Chin This Palmer Research White Paper was commissioned by NETGEAR and is distributed under license from Palmer [email protected] 2014 Palmer Research. All Rights Reserved.Page 23345678

Executive SummaryAs usage of smart phones and tablets continue to gain in popularity, the trend towards BYOD (bring your own device)continues to gain momentum. Wireless networks that were once designed to support a few laptop computers must nowroutinely host a wide range of mobile devices including smartphones, tablet computers, and e-readers, often with thesedevices running bandwidth-intensive applications such as video. As a result, IT administrators are increasingly faced with thechallenge of how to design and deploy a wireless network that can accommodate the exponential growth in network devicesand applications.This whitepaper is intended to help IT administrators understand some basic guidelines for determining access point (AP)throughput, bandwidth requirements and best practices for wireless deployment in high density environments such as schoolsand small/medium businesses.IntroductionThere are two basic types of deployment models in wireless: coverage and capacity based. In a coverage based wirelessdesign, the goal is to provide good quality of service (in terms of RF signal strength) in as much of the area as possible with asingle or multiple access points. Examples of coverage based deployments include sites where there is a relatively large areawith few Wi-Fi devices per user such as: Elementary school classrooms Warehouses Nursing homes, hospitals and clinics Hotels Office cubiclesIn most of these deployments, the number of access points needed to cover the area is determined by the AP signal strength,which is a combination of AP output power and antenna gain. Other factors to consider when designing coverage basednetworks are: Type of site - office, cubicle, warehouse, single room motel/hotel, etc. Floor plan and ceiling height – e.g. office (10 ft./3 m), warehouse (20 ft./3m), gym (30 ft./9m) Construction materials and obstructions - e.g. concrete, brick, drywall, elevator shafts Number of floors Exclusion areas – locations where coverage is not needed/wantedPage 3

The second type of wireless deployment is referred to as capacity based. In this type of deployment, the goal is to providegood quality wireless service to a concentrated set of concurrent users in a confined area. Examples of capacity baseddeployments include sites such as middle or high school classrooms, lecture halls, auditoriums, libraries, stadiums, and officeconference rooms. Factors to consider when designing capacity based networks are: Number of users in a specific area covered by a single AP Number of Wi-Fi devices per person Percentage of users that are expected to be active Types of applications and throughput needed Mix of applications Type of clients in the network (2.4 GHz vs. 5GHz) Legacy vs. .11n client protocolsWithin an enterprise or school, there may be a mix of areas that require both coverage and capacity based wirelessdeployments. When you have a large number of users accessing Wi-Fi and demanding throughput at the same time, it isconsidered to be a high density area. As a general rule of thumb, when there are 25 to 30 active users in a coverage areaserved by a single AP (approximately 500 to 1,000 square feet), then you will need to design your wireless network usingsome of the high density best practices that are outlined in this guide.Determining Access Point ThroughputIt is a common sizing mistake to use the theoretical maximum to estimate how much throughput an AP can actuallysupport, For example, the theoretical throughput for an access point with a 2x2 dual band radio that can support up to300Mbps per radio would be 600 Mbps (300Mbps x 2). Assuming there are 25 concurrent Wi-Fi users in the area, youcould mistakenly calculate that each access point can support 24Mbps per user (600Mbps/25 users).In practice, there are several factors that will significantly reduce AP throughput vs. the theoretical limit: Protocol and packet overhead - can reduce throughput by 40 - 50% Slow or “far away” clients - clients that are further away or in an area of weaker signal strength must step downthe transmission physical rate (PHY) rate to send the packet (e.g. a client sending a packet at 1 Mbps will take 100times longer than a client sending the same packet at a PHY rate of 100Mbps), potentially causing an additional 50%degradation of throughput. Uneven distribution of clients - in a dual band concurrent AP, both bands can simultaneously support client traffic.However, not all clients are dual band and there is no guarantee that even the dual band clients will evenly distributethemselves between 2.4 and 5GHz. Network effectiveness may be reduced by another 50% due to the behavior ofthe clients. Control traffic – control traffic exchanged between the AP and various clients at low PHY rates can further reduceavailable bandwidth by 25%. Other – co-channel and adjacent channel interference, network re-transmissions, and bad behavior clients willfurther reduce AP throughput.Page 4

As you can see in Figure 1, end users in schools and small/medium businesses are only left with 2 -3 Mbps/user to run missioncritical applications after taking into account the various factors constraining AP throughput. Note that these values are offered as anexample based on experience with past solutions and actual performance may vary based on situational conditions.Figure 1: Realistic User ThroughputEstablishing Bandwidth RequirementsWhen designing high density wireless networks, it is critical to understand which applications will be used and how much bandwidtheach application will consume in terms of throughput per user. The chart in Figure 2 below provides some general references on howmuch throughput is needed for common applications such as internet, audio, video, printing, file sharing, and online testing. More andmore schools are using online video applications such as knowmia.com and youtube.com as a daily teaching tool. As you can see fromthe chart, throughput requirements can vary from 2 to 4Mpbs per user depending on the video resolution. Once the bandwidth perapplication is known, this number can be used to calculate the bandwidth required per user.Figure 2: Average Bandwidth Requirements by Application TypePage 5

In addition to the type of applications to be used, bandwidth requirements will vary based on the number of expected userson the wireless network. As more users access the network, throughput per user goes down causing slower transmissionrates. If the network consists of mixed clients (11a, b, gand 11n modes), the average throughput per client will also go downwith the greater the number of legacy clientsOnce the types of applications are identified and the bandwidth per type of application is determined, you can establish theaggregate bandwidth required by multiplying the total Mbps by the number of expected users in the coverage area.Top 10 High Density Design RecommendationsThe following design recommendations are best practices based on many successful installations and should serve asguidelines for proper design, planning, and deployment of a wireless network in a high density environment.1) Identify High Density Areas - start the design process by using a live RF tool such as AirMagnet planner to identifyareas of high density.2) Use Dual Band APs - use dual band concurrent access points (2.4GHz and 5 GHz radios) to maximize availablethroughput for users. Always enable both radios.3) Design AP Overlap - design the AP placement in high density areas such that each client always sees two to threeaccess points. If one or two access point is overloaded at any given time, the client can be load balanced to anotheraccess point without any negative impact to the end user.Figure 3: Design AP Overlap for High Density Areas4) Load Balance Traffic - set the threshold on the AP to effectively utilize an over the air resource to ensure that youload balance the traffic to all of the access points that can be seen by clients. Based on Netgear’s internal testing, werecommend setting the maximum number of clients to 25 to 30 for high throughput applications and the minimum RSSIthreshold of (-73dBm). This means that any particular AP will serve a maximum of 25 to 30 clients with good reception.5) One AP Per Classroom - for middle or high schools that have 25 to 30 students per classroom and have highthroughput traffic as part their daily classroom teaching due to 1:1 programs or HD video streaming, use one AP perclassroom and an additional AP in the hallway.Page 6

6) Set AP Power Lower – turning AP power up could cause additional co-channel and adjacent-channel interference.The recommended method is adding a third AP while setting the output power to one half or one quarter for the2.4GHz AP and to one half for the 5 GHz AP.Figure 4: Tuning AP Output for Maximum Power7) Upgrade the Wired Network – ensure that there is sufficient bandwidth on the wired network to support higherthroughput APs by deploying PoE Gig switches at the edge and 1G or 10G switches at the aggregation/core layer.8) Go Onsite – conduct a physical site survey to identify and trouble shoot any potential forms of interference fromWi-Fi or non-Wi-Fi sources.9) Stress Test – prior to live deployment, fully load the network to validate the ability of the network to handle theamount of traffic generated by a BYOD implementation.10) Share Knowledge – high density wireless design is still a relatively new topic among IT administrators in K-12 educationand SMBs. Sharing knowledge of best practices from other successful deployments can be a valuable resource.ConclusionAs BYOD becomes a way of life, not just in business environments but in facilities like schools, hospitals and even governmentbuildings, wireless networks must be-designed to accommodate significant increases in the amount of traffic generated . Inhigh density environments, the demands on throughput are often exacerbated by users carrying two or three devices usingmultiple applications that consume network resources simultaneously. The key to a successful wireless deployment is firstunderstanding whether your environment is coverage or capacity based. Once you assess the parameters based on thedeployment scenario, following the design recommendations outlined in this document should ensure sufficient bandwidthcapacity to deliver a positive experience for end users. Sharing best practices with colleagues who have implemented or are inthe process of implementing wireless networks in other schools and small/medium businesses can also be a valuable resource.Page 7

About NETGEARNETGEAR is a global networking company that offers reliable, affordable and easy to use solutions that have beenspecifically designed to meet the needs of small businesses and educational institutions. NETGEAR Access Points andWireless Controllers give schools a powerful, cost-effective wireless solution that can fulfill the promise of connectedlearning simply and quickly. With NETGEAR Education Solutions, schools and small businesses gain: Lower Total Cost of Ownership for size of deployment (5-20 AP)A simple web-based UI for easy management and accessPartner support and planningA full portfolio of Access Points and Wireless Management ControllersWhether you are in the exploration, project definition, implementation, or expansion stage for coverage or capacity basedwireless, NETGEAR can provide guidance and advice to help design robust, secure and flexible networks through ourextensive and experienced reseller channel. For more information, go to www.netgear.com.About Debra chinDebra joined Palmer Research in 2006 as Senior Vice President. Her background includes over 15 years of experiencein executive level marketing and research positions for leading consumer packaged goods and high tech companies. Sheholds an MBA from Columbia Business School and a BSE in Economics from the Wharton School of Business. Foundedin 2001, Palmer Research delivers the information and intelligence IT decision makers and high tech companies need tobetter understand market dynamics and meet their business objectives. The company is located in Los Altos, CA. For moreinformation, go to www.palmerresearchgroup.com.NETGEAR, the NETGEAR logo, ReadyCLOUD and ReadyNAS are trademarks and/or registered trademarks of NETGEAR, Inc. and/or its subsidiaries in theUnited States and/or other countries. Other brand names mentioned herein are for identification purposes only and may be trademarks of their respectiveholder(s). Information is subject to change without notice. 2013 NETGEAR, Inc. All rights reserved.Page 8