High-Density Wireless Networks for Auditoriums Validated Reference Design. Solution Guide

Transcription

1 High-Density Wireless Networks for Auditoriums Validated Reference Design Solution Guide

2 Copyright 2010 Aruba Networks, Inc. AirWave, Aruba Networks, Aruba Mobility Management System, Bluescanner, For Wireless That Works, Mobile Edge Architecture, People Move. Networks Must Follow, RFprotect, The All Wireless Workplace Is Now Open For Business, Green Island, and The Mobile Edge Company are trademarks of Aruba Networks, Inc. All rights reserved. Aruba Networks reserves the right to change, modify, transfer, or otherwise revise this publication and the product specifications without notice. While Aruba uses commercially reasonable efforts to ensure the accuracy of the specifications contained in this document, Aruba will assume no responsibility for any errors or omissions. Open Source Code Certain Aruba products include Open Source software code developed by third parties, including software code subject to the GNU General Public License ( GPL ), GNU Lesser General Public License ( LGPL ), or other Open Source Licenses. The Open Source code used can be found at this site: Legal Notice ARUBA DISCLAIMS ANY AND ALL OTHER REPRESENTATIONS AND WARRANTIES, WEATHER EXPRESS, IMPLIED, OR STATUTORY, INCLUDING WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, TITLE, NONINFRINGEMENT, ACCURACY AND QUET ENJOYMENT. IN NO EVENT SHALL THE AGGREGATE LIABILITY OF ARUBA EXCEED THE AMOUNTS ACUTALLY PAID TO ARUBA UNDER ANY APPLICABLE WRITTEN AGREEMENT OR FOR ARUBA PRODUCTS OR SERVICES PURSHASED DIRECTLY FROM ARUBA, WHICHEVER IS LESS Crossman Avenue Sunnyvale, California Phone: Fax High-Density Wireless Networks for Auditoriums Validated Reference Design Solution Guide October 2010

3 Contents Chapter 1 Introduction 7 About Aruba Networks 7 Aruba Validated Reference Designs 7 Solution Guide Assumptions and Scope 8 Design Validation and Testing 9 Reference Documents 9 Chapter 2 Design Requirements for Auditorium HD WLANs 11 Functional Requirements 12 Technical Requirements Client Devices 13 Technical Requirements Wired Infrastructure 13 Technical Requirements Wireless Infrastructure 14 Chapter 3 Capacity Planning for HD-WLANs 17 HD WLAN Capacity Planning Methodology 17 Step #1: Choose a High-Density WLAN Capacity Goal 18 Step #2: Determine the Usable Number of Channels MHz vs. 40-MHz Channels 19 Available 5-GHz Channels 20 To DFS or Not to DFS? 22 Site-Specific Restrictions 22 5-GHz Channel Reuse 23 Available 2.4-GHz Channels GHz Channel Reuse 24 Step #3: Choose a Concurrent User Target 25 Mixed Auditoriums with Both n and Legacy Clients 25 Choosing a Concurrent User Target 27 Step #4: Predict Total Capacity 27 5-GHz Capacity GHz Capacity 29 Step #5: Validate the Capacity Goal 29 Chapter 4 RF Design for HD WLANs 31 Coverage Strategies for Auditoriums 31 Overhead Coverage 32 Side Coverage (Walls or Pillars) 35 Floor Coverage (Picocells) 38 Choosing Access Points and Antennas 40 Recommended Products 41 Choosing an Access Point 44 External Antenna Selection 44 Minimum Spacing Between Adjacent Channel APs 45 AP and Antenna Spacing Overhead and Underfloor Strategies 45 AP and Antenna Spacing Side Coverage Strategy 46 Aesthetic Considerations 47 High-Density Wireless Networks for Auditoriums VRD Solution Guide Contents 3

4 General Installation Best Practices 48 Managing Adjacent HD WLANs 48 Managing Clients 48 Overhead or Floor Coverage 49 Side Coverage with Directional Antennas in Series 49 Side Coverage with Back-to-Back APs and Directional Antennas 50 Chapter 5 Infrastructure Optimizations for HD WLANs 51 Essential ArubaOS Features for HD WLANs 51 Achieving Optimal Channel Distribution 51 ARM Channel Selection 52 Mode-Aware ARM 52 Achieving Optimal Client Distribution 53 Band Steering 53 Spectrum Load Balancing 54 Optimal Power Control 54 How ACI and CCI Reduce WLAN Performance 54 How the Carrier Sense Works 55 How Adjacent Channel Interference Reduces WLAN Performance 55 How Co-Channel Interference Reduces WLAN Performance 58 Limiting AP Transmitter Power 60 Limiting Client Transmitter Power 60 Enabling the Aruba RX Sensitivity Tuning-Based Channel Reuse Feature 60 Optimal Airtime Management 61 Ensuring Equal Access with Airtime Fairness 61 Limiting Chatty Protocols 63 Maximizing Data Rate of Multicast traffic 64 Enabling Dynamic Multicast Optimization for Video 64 Limiting Supported Legacy Data Rates 65 Other Required Infrastructure Settings 65 VLAN Pooling 65 Chapter 6 Configuring ArubaOS for HD-WLANs 67 Achieving Optimal Channel Distribution 68 Enabling ARM Channel/Power Selection 68 Enabling Mode-Aware ARM 69 Enabling DFS Channels 70 Achieving Optimal Client Distribution 71 Enabling Band Steering 71 Enabling ARM Spectrum Load Balancing 72 Achieving Optimal Power Control 73 Reducing AP Transmitter Power 73 Limiting Client Transmitter Power 74 Minimizing CCI with RX Sensitivity Tuning-Based Channel Reuse 74 Achieving Optimal Airtime Management 76 Enabling Airtime Fairness 76 Limiting Chatty Protocols 77 Implementing Multicast Enhancements 78 Enabling Multicast Rate Optimization 78 Enabling IGMP Snooping 80 Enabling Dynamic Multicast Optimization for Video 80 Video Scalability 81 Reducing Rate Adaptation by Eliminating Low Legacy Data Rates 82 Other Required Infrastructure Settings 83 VLAN Pooling 83 4 Contents High-Density Wireless Networks for Auditoriums VRD Solution Guide

5 Chapter 7 Troubleshooting for HD WLANs 85 Scoping the Problem 85 End-to-End Solution Framework 86 HD WLAN Troubleshooting 86 Troubleshooting Flow Chart 87 Symptom #1: Device cannot see any SSIDs 88 Symptom #2: Device can see SSIDs but not the one it needs 88 Symptom #3: Device successfully authenticates but cannot communicate 90 Symptom #4: Device has Connection Loss and/or Poor Performance 91 Before You Contact Aruba Support 92 Appendix A HD WLAN Testbed 95 Testbed Design 95 What is a Client Scaling Test? 95 Testbed Design 95 Test Plan Summary MHz Channel Tests MHz Channel Tests 97 Adjacent Channel Interference Tests 98 Co-Channel Interference Tests 98 Test Results: 20-MHz Channel 99 How does total channel capacity change as clients are added? 99 How does per-client throughput change as clients are added? 101 How much does throughput decrease as legacy stations are added? 102 How many stations can contend before channel capacity declines? 102 Is there a limit to the number of concurrent users an AP can serve? 103 Test Results: 40-MHz Channel 103 How does total HT40 channel capacity change as clients are added? 103 How does per-client HT40 throughput change as clients are added? 104 Appendix B Advanced Capacity Planning Theory for HD WLANs 107 Predicting Total Capacity 107 Predicting Device Counts Using a Radio Budget 107 Predicting Performance Using a Throughput Budget 109 Capacity Planning Methodology for HD WLANs 111 Appendix C Basic Picocell Design 113 RF Design for Picocell 113 Understanding Structure of a Picocell 114 Link Budget Analysis 115 Minimum Channel Reuse Distance 116 Capacity Planning for Picocell 117 Reconciling the RF and Capacity Plans 117 Appendix D Dynamic Frequency Selection Operation 119 Behavior of 5-GHz Client Devices in Presence of Radar 119 Behavior and Capabilities of 5 GHz Client Devices 120 DFS Summary 120 Appendix E Aruba Contact Information 121 Contacting Aruba Networks 121 High-Density Wireless Networks for Auditoriums VRD Solution Guide Contents 5

6 6 Contents High-Density Wireless Networks for Auditoriums VRD Solution Guide

7 Chapter 1 Introduction This guide explains how to implement an Aruba n wireless network that must provide high-speed access to an auditorium-style room with 500 or more seats. Aruba Networks refers to such networks as high-density wireless LANs (HD WLANs). Lecture halls, hotel ballrooms, and convention centers are common examples of spaces with this requirement. Because the number of concurrent users on an AP is limited, to serve such a large number of devices requires access point (AP) densities well in excess of the usual AP per 2,500 5,000 ft 2 ( m 2 ). Such coverage areas therefore have many special technical design challenges. This validated reference design provides the design principles, capacity planning methods, and physical installation knowledge needed to successfully deploy HD WLANs. About Aruba Networks Aruba delivers secure enterprise networks wherever users work or roam. Our mobility solutions bring the network to you reliably, securely, and cost-effectively whether you're working in a corporate office, teaching space, hospital, warehouse, or outdoors. Aruba n WLANs reduce the need for wired ports, which lowers operating costs. Our remote access point technology brings the network to branch offices, home offices, or temporary locations with plug-and-play simplicity, and all of the heavy lifting stays at the data center. For customers with legacy wireless LANs, our AirWave multivendor management tool supports WLAN devices from 16 manufacturers, which allows you to seamlessly manage old and new networks from a single console. Aruba Validated Reference Designs An Aruba validated reference design (VRD) is a package of product selections, network decisions, configuration procedures and deployment best practices that comprise a reference model for common customer deployment scenarios. Each Aruba VRD has been constructed in a lab environment and thoroughly tested by Aruba engineers. By using these proven designs, our customers are able to rapidly deploy Aruba solutions in production with the assurance that they will perform and scale as expected. Aruba publishes two types of validated reference designs, base designs and incremental designs. Figure 1 illustrates the relationship between these two types of designs in the Aruba validated reference design library. Figure 1 Aruba Validated Reference Design Library Optimizing Aruba WLANs for Roaming Devices Wired Multiplexer (MUX) High-Density Wireless Networks Incremental Designs Campus Wireless Networks Retail Wireless Networks Virtual Branch Networks Base Designs HD_190 High-Density Wireless Networks for Auditoriums VRD Solution Guide Introduction 7

8 A base design is a complete, end-to-end reference design for common customer scenarios. Aruba publishes the following base designs: Campus Wireless Networks VRD: This guide describes the best practices for implementing a large campus wireless LAN (WLAN) that serve thousands of users spread across many different buildings joined by SONET, MPLS, or any other high-speed, high-availability backbone. Retail Wireless Networks VRD: This guide describes the best practices for implementing retail networks for merchants who want to deploy centrally managed and secure WLANs with wireless intrusion detection capability across distribution centers, warehouses, and hundreds or thousands of stores. Virtual Branch Networks VRD: This guide describes the best practices for implementing small remote networks that serve fewer than 100 wired and wireless devices that are centrally managed and secured in a manner that replicates the simplicity and ease of use of a software VPN solution. An incremental design provides an optimization or enhancement that can be applied to any base design. Aruba publishes the following incremental designs: High-Density Wireless Networks VRD (this guide): This guide describes the best practices for implementing coverage zones with high numbers of wireless clients and APs in a single room such as lecture halls and auditoriums. Optimizing Aruba WLANs for Roaming Devices VRD: This guide describes best the practices for implementing an Aruba wireless network that supports thousands of highly mobile devices such as Wi-Fi phones, handheld scanning terminals, voice badges, and computers mounted to vehicles. Wired Multiplexer (MUX) VRD: This guide describes the best practices for implementing a wired network access control system that enables specific wired Ethernet ports on a customer network to benefit from Aruba role-based security features. Solution Guide Assumptions and Scope This guide is an incremental design. It addresses advanced radio frequency (RF) design topics, and it is intended for experienced WLAN engineers. This design builds on the base VRDs that Aruba has published (Campus Wireless Networks, Retail Wireless Networks, and Virtual Branch Networks). A properly implemented master/local design is a prerequisite to proceed with this High-Density VRD. This guide is based on ArubaOS version This guide makes assumptions about the knowledge level of the engineer, the existing architecture and configuration of the Aruba WLAN, and the AP type and wireless frequency band that will be used. Table 1 lists these assumptions. Table 1 Solution Guide Assumptions Category Assumption Engineer Knowledge Level Thorough understanding of and experience with RF design principles, link budgets, RF behaviors, antenna selection, regulatory bodies, and allowable channel/power combinations, with Certified Wireless Network Administrator (CWNA) level or equivalent. Thorough understanding of MAC layer operation, beacons, probes, rate adaption, retries, CSMA/CA. Experience with spectrum analysis and troubleshooting RF problems. Comfort with controller-based WLAN architectures that employ thin APs. Thorough understanding of Aruba controller design, master/local architectures, and controller and AP redundancy. 8 Introduction High-Density Wireless Networks for Auditoriums VRD Solution Guide

9 Table 1 Solution Guide Assumptions (Continued) Category Assumption Existing Aruba Configuration Base design was architected using one or more master/local clusters that conforms to the Campus, Retail (for example, distributed), or Virtual Branch Networks VRDs. Complete control over the RF airspace; freedom to choose any combination of channels and power levels that are legal within the country/regulatory domain. High-Density WLAN Design 5 GHz is the primary band for servicing clients and all 5-GHz-capable clients will be steered to that band; 2.4 GHz will accommodate legacy devices or provide overflow capacity for 5 GHz n is required, with Gigabit Ethernet connections between each AP and the IDF to support peak AP throughputs. High-throughput 20-MHz (HT20) channels are used exclusively in HD WLAN coverage zones to increase capacity. 40-MHz channels are not used in HD WLAN coverage zones. Channels are not reused inside any single auditorium. However, reuse may occur for adjacent HD WLANs or adjacent conventional WLAN deployments. (See Appendix C, Basic Picocell Design on page 113 for discussion of advanced designs requiring reuse in a single room.) Clients are stationary and evenly distributed within each auditorium. The infrastructure may influence them to roam to balance the load. Design Validation and Testing Test cases for this VRD were executed against the RF design and physical architecture recommended in this guide using a heterogenous mix of up to 50 late-model laptops with varying operating systems, CPUs, and wireless network adapters. This mix approximates actual conditions in a typical auditorium. Aruba 3000 Series controllers were tested with AP-120 Series and AP-105 Series access points. ArubaOS release was used to conduct these tests. Ixia Chariot 7.1 was used to produce repeatable controlled test loads that were used to characterize relative performance of various design choices. More information on test methodology can be found in Chapter 3, Capacity Planning for HD-WLANs on page 17 and Appendix A, HD WLAN Testbed on page 95. Reference Documents The following technical documents provide additional detail on the technical issues found in HD WLANs: ARM Yourself to Increase Enterprise WLAN Data Capacity, Gokul Rajagopalan and Peter Thornycroft, Aruba Networks, 2009 Adaptive CSMA for Scalable Network Capacity in High-Density WLAN: a Hardware Prototyping Approach, Jing Zhu, Benjamin Metzler, Xingang Guo and York Liu, Intel Corporation, 2006 Next Generation Wireless LANs: Throughput, Robustness, and Reliability in n, Eldad Perahia and Robert Stacey, Cambridge University Press, 2008 Own the Air: Testing Aruba Networks Adaptive Radio Management (ARM) in a High-Density Client Environment, Network Test Inc., July 2010 Data sheets for Aruba AP-105, AP-124, and AP-125 access points Data sheets for Aruba AP-ANT-13B, AP-ANT-16, AP-ANT-17, and AP-ANT-18 external antennas High-Density Wireless Networks for Auditoriums VRD Solution Guide Introduction 9

10 10 Introduction High-Density Wireless Networks for Auditoriums VRD Solution Guide

11 Chapter 2 Design Requirements for Auditorium HD WLANs HD WLANs are defined as RF coverage zones with a large number of wireless clients and APs in a single room. With the proliferation of wireless-enabled personal and enterprise mobile devices, a surprisingly diverse range of facilities need this type of connectivity: Large meeting rooms Lecture halls and auditoriums Convention center meeting halls Hotel ballrooms Stadiums, arenas, and ballparks Press areas at public events Concert halls and ampitheaters Airport concourses Financial trading floors Casinos This VRD addresses auditorium-style areas. When you understand the auditorium scenario, it is quite straightforward to apply the design principles to almost any type of high-density coverage zone. The high concentration of users in any high-density environment presents challenges for designing and deploying a wireless network. The explosion of Wi-Fi-enabled smartphones means that each person could have two or more NICs vying for service, some of which may be capable of only 2.4-GHz communication. At the same time, maximum HD WLAN capacity varies from country to country based on the number of available radio channels. Balancing demand, capacity, and performance in this type of wireless network requires careful planning. This chapter defines the functional and technical requirements of the auditorium scenario, including those for client devices, wired infrastructure, and wireless infrastructure. Understanding these requirements sets the stage for the design, configuration, and troubleshooting chapters to follow. High-Density Wireless Networks for Auditoriums VRD Solution Guide Design Requirements for Auditorium HD WLANs 11

12 Functional Requirements The typical auditorium addressed by this VRD has a total target capacity of 500 seats. If each user is carrying a laptop and a Wi-Fi-enabled PDA or smartphone, the total WLAN client count could be as high as 1,000 devices. The average real-world, per-client bandwidth need is usually no more than 1 Mbps even for many video streaming deployments. In Chapter 3, Capacity Planning for HD-WLANs on page 17, we discuss how higher or lower throughput targets alter the total capacity of an HD WLAN. Figure Seat University Lecture Hall The users in an auditorium are evenly distributed across the space because they are usually sitting in rows of stadium-type seating. The user density in the seating areas is an average of 1 user per 15 ft 2 (5 m 2 ), including aisles and other common areas. As many as 20 APs could be deployed in a single auditorium, depending on the total number of allowed channels in the regulatory domain. Available mounting locations are often less than ideal, and aesthetic and cable routing considerations limit installation choices. Figure 3 shows the user density in a typical auditorium or lecture hall environment. Figure 3 Auditorium of 320 Seats with Typical Dimensions 12 Design Requirements for Auditorium HD WLANs High-Density Wireless Networks for Auditoriums VRD Solution Guide

13 The user density of the typical auditorium is approximately 20 times greater than an office environment. In a typical office environment with a mix of cubicles and offices, a typical client density is ft 2 (23 to 33 m 2 ) per person, including common areas, with a per-client bandwidth need of 500 Kbps or less. It is common to deploy one AP every 2,500 to 5,000 ft 2 (225 to 450 m 2 ), which provides for average received signal strengths of -65 to -75 dbm depending on the walls and other structures in the area. Also, the office environment provides much more flexibility in AP mounting and placement choices. In universities and convention centers, it is common for several auditoriums of varying capacities to exist side-by-side or above-and-below. This situation makes the design aspect even more challenging because the rooms are almost always adjacent and close enough to require careful management of cochannel interference (CCI) and adjacent channel interference (ACI) between auditoriums. This situation can include intended and unintended RF interaction between APs, clients, and between clients in different rooms. As a result, such facilities require special RF design consideration, which is covered in Chapter 4, RF Design for HD WLANs on page 31. Technical Requirements Client Devices Understanding and controlling the output power and roaming behavior of the client devices is an essential requirement for any HD WLAN. Client radios greatly outnumber AP radios in any high-density coverage zone and therefore they dominate the CCI/ACI problem h and Transmit Power Control (TPC) are critical, but they are totally dependent on the client WLAN hardware driver. Encouraging or requiring users to implement these features will greatly improve overall client satisfaction. The usage profile of most dense auditorium environments is a heterogeneous, uncontrolled mix of client types. The devices are not owned and controlled by the facility operator, so they cannot be optimized or guaranteed to have the latest drivers, wireless adapters, or even application versions. Any operating system of any vintage or device form factor could be in use. Network adapters could be any combination of a, b, g, and n. Users of the wireless network in an auditorium expect moderate throughput, high reliability, and low latency. Concurrent usage and initial connection is of primary concern in the design and configuration. Some common small handheld devices, such as the iphone, go into a low power state frequently and cause a reconnection to the WLAN periodically. This demand puts more control path load on the WLAN infrastructure and it must be considered in the design. The user traffic in an auditorium WLAN is a variety of application types. Some of the most common applications in the auditorium WLAN are HTTP/HTTPS traffic, , and collaboration and custom classroom applications. Custom applications in an auditorium include classroom presentation and exam applications, as well as multicast streaming video applications. With the exception of video, these applications are bursty in nature and require concurrent usage by many or all of the wireless clients. Therefore, this VRD assumes that fair access to the medium is a fundamental requirement. Technical Requirements Wired Infrastructure The user density and heterogeneous client mix inherent in the auditorium HD WLAN scenario also places a number of unique requirements on the wired network infrastructure. Some key requirements are: Gigabit Ethernet (GbE) Edge Ports with 802.3af or 802.3at: This guide assumes n APs, which provide up to 300 Mbps per radio. This speed in turn requires gigabit connections at the edge. 10-Gigabit Ethernet Uplinks to Distribution Switches: Most, if not all, APs in each auditorium will terminate on the same IDF, so edge switch backplanes and uplinks must be sized for the expected peak aggregate throughput from the HD WLAN. High-Density Wireless Networks for Auditoriums VRD Solution Guide Design Requirements for Auditorium HD WLANs 13

14 Simultaneous Logins/Logoffs: The RADIUS or other authentication server must be able to handle the inrush and outrush of users at fixed times (such as a class start and stop bell). Ensure that the AAA server can accommodate the expected peak number of authentications per second. You can use the Aruba command show aaa authentication-server radius statistics to monitor average response time. IP Address Space: Sufficient addresses must be available to support not only laptops but also smartphones and other future Wi-Fi-compatible devices that may expect connectivity. Some surplus space will be necessary to support inrush and outrush of users in a transparent fashion and in concert with the DHCP service lease times in order to prevent address exhaustion. DHCP Service: The DHCP server for the HD WLAN must also be able to accommodate an appropriate inrush peak load of leases per second. Lease times must be optimized to the length of sessions in the room so that the address space can be turned over smoothly between classes or meetings. Technical Requirements Wireless Infrastructure HD WLANs also require specific capabilities in the wireless infrastructure, including: Adaptive Radio Management (ARM) Dynamic RF Management: To minimize the IT administration burden and enable HD WLANs to adapt to changing RF conditions, dynamic channel and power selection features are a requirement. So are dynamic client distribution features including the ability to steer 5-GHz-capable clients to that band and spectrum load balancing to ensure even allocation of clients across available channels. Because there are many fewer 2.4-GHz channels than 5-GHz channels, another requirement is that the minimum number of 2.4-GHz radios are enabled inside each HD WLAN. This requires either an automatic coverage-management feature, such as the Aruba Mode-Aware ARM to convert surplus 2.4-GHz radios into air monitors to prevent unnecessary CCI. Alternatively, a static channel plan may be used in the 2.4-GHz band in parallel with ARM in the 5-GHz band. ARM Airtime Fairness: Airtime fairness is basic requirement of any heterogenous client environment with an unpredictable mix of legacy and new wireless adapters. Older a/b/g clients that require more airtime to transmit frames must not be allowed to starve newer highthroughput clients. The ARM Airtime Fairness algorithm uses infrastructure control to dynamically manage the per-client airtime allocation. This algorithm takes into account the traffic type, client activity, and traffic volume before allocating airtime on a per-client basis for all its downstream transmissions. This ensures that with multiple clients associated to the same radio, no client is starved of airtime and all clients have acceptable performance. VLAN Pooling: There must be adequate address space to accommodate all of the expected devices, including a reserve capacity for leases that straddle different meetings in the same room. At the same time, limiting the broadcast domain size is crucial to limiting over-the-air management traffic. Aruba s VLAN Pooling feature provides a simple way to allocate multiple /24 subnets to accommodate any size auditorium. Disabling Low Rates: By definition, any high-density coverage area has APs and clients in a single room or space. To minimize unnecessary rate adaptation due to higher collision activity, it is a requirement to reduce the number of supported rates. This may be accomplished by just enabling Mbps legacy OFDM rates. However, all n MCS rates must be enabled for compatibility with client device drivers. Chatty Protocols: A chatty protocol is one that sends small frames at frequent intervals, usually as part of its control plane. Small frames are the least efficient use of scarce airtime, and they should be reduced whenever possible unless part of actual data transmissions. Wherever chatty protocols are not needed, they should be blocked or firewalled. These protocols include IPv6 if it is not in production use, netbios-ns, netbios-dgm, Bonjour, mdns, UPnP, and SSDP. 14 Design Requirements for Auditorium HD WLANs High-Density Wireless Networks for Auditoriums VRD Solution Guide

15 Dynamic Multicast Optimization (DMO): DMO makes reliable, high-quality multicast transmissions over WLAN possible. To ensure that video data is transmitted reliably, multicast video data is transmitted as unicast, which can be transmitted at much higher speeds and has an acknowledgement mechanism to ensure reliability. Transmission automatically switches back to multicast when the client count increases high enough that the efficiency of unicast is lost. IGMP Snooping: Ensures that the wired infrastructure sends video traffic to only those APs that have subscribers. Multicast-Rate-Optimization (MRO): Multicast over WLAN, by provision of the standard, needs to be transmitted at the lowest supported rate so that all clients can decode it. MRO keeps track of the transmit rates sustainable for each associated client and uses the highest possible common rate for multicast transmissions. Quality of Service (QoS): If voice or video clients are expected in the HD WLAN, it is essential that QoS be implemented both in the air as well as on the wire, end-to-end between the APs and the media distribution infrastructure. Receive Sensitivity Tuning: Receive sensitivity tuning can be used to fine tune the APs to ignore clients that attempt to associate at a signal level below what is determined to be the minimum acceptable for a client in the intended coverage zone. This tuning helps to reduce network degradation to outside interference and/or client associations that may be attempted below the minimum acceptable signal level based on the desired performance criteria. High-Density Wireless Networks for Auditoriums VRD Solution Guide Design Requirements for Auditorium HD WLANs 15

16 16 Design Requirements for Auditorium HD WLANs High-Density Wireless Networks for Auditoriums VRD Solution Guide

17 Chapter 3 Capacity Planning for HD-WLANs Over the next four chapters you will learn capacity planning, RF design, configuration, and validation for HD WLANs. In this chapter, you will learn the basic approach to planning an HD WLAN and making a first-order assessment of whether the desired level of performance is possible for an area of a given size. This chapter uses charts and lookup tables to provide the wireless architect with the necessary sizing parameters. These tables are based on extensive validation testing conducted in the Aruba labs. For those interested in the mathematics and theory of HD WLAN design behind the charts, Appendix B, Advanced Capacity Planning Theory for HD WLANs on page 107 provides a technical explanation of the process. HD WLAN Capacity Planning Methodology The process of sizing an HD WLAN is straightforward if you have the benefit of certain test data and an accurate database of allowable channels in each country. You will follow the same five steps for each coverage zone you plan: Choose capacity goal Validate against goal Determine usable channel count Predict total capacity Choose concurrent user target HD_ Choose a capacity goal: The first step is to pick an application-layer throughput target linked to the seating capacity of the auditorium. 2. Determine the usable number of channels: For each band, decide how many nonoverlapping channels are usable for the HD WLAN. Use a database of regulatory information included here, augmented by site-specific decisions such as whether or not Dynamic Frequency Selection (DFS) channels are available. 3. Choose a concurrent user target: Determine the maximum number of simultaneously transmitting clients that each AP will handle. Use a lookup table based on test data supplied by Aruba. You must do this for each radio on the AP. 4. Predict total capacity: Use the channel and concurrent user count limits to estimate the maximum capacity of the auditorium using lookup tables supplied by Aruba. 5. Validate against capacity goal: Compare the capacity prediction with the capacity goal from step 1. If the prediction falls short, you must start over and adjust the goal, concurrent user limit, or High-Density Wireless Networks for Auditoriums VRD Solution Guide Capacity Planning for HD-WLANs 17

18 channel count until you have a plan that you can live with. For large auditoriums over 500 seats, you should be prepared to accept a per-client throughput of 500 Kbps or less, assuming a 50/50 mix of.11n and.11a stations and nine usable channels. NOTE This guide assumes that channels will not be reused within a single auditorium. If Channel reuse is required to achieve the capacity goal, see Appendix C, Basic Picocell Design on page 113 for an advanced discussion of the theoretical issues involved in managing AP-to-AP and clientto-client interference. In practice, reuse is extremely difficult to achieve in most auditoriums due to their relatively small size and the signal propagation characteristics of multiple-in multiple-out (MIMO) radios. Reuse requires more complex calculations and testing as well as the potential for modifying physical structures in the user environment. Step #1: Choose a High-Density WLAN Capacity Goal Every HD WLAN design begins by defining a capacity goal. This goal has two parts, which are the key factors are necessary for the designer to properly scale and produce a HD WLAN project design. Total number of devices: Often, this is just equal to the seating capacity of the area. Sometimes, each seat may contain more than one client (that is, one laptop and one Wi-Fi-capable smartphone). This is important because every MAC address consumes airtime, an IP address, and other network resources. Minimum bandwidth per device: This is primarily driven by the mix of data, voice, and video applications that will be used in the room. Aruba recommends using LAN traffic studies to precisely quantify this value. Here are some common examples of a complete capacity goal: Each classroom has 30 students who each need 2 Mbps of symmetrical throughput. The auditorium holds 500 people. Each one has a laptop that must have at least 350 Kbps for data and a voice handset that requires at least 128 Kbps. The trading floor must serve 800 people with at least 512 Kbps each. Each of these scenarios provides the wireless architect with a clear, concise, and measurable end state. It s a good idea to build in future capacity needs. While the number of seats in the auditorium is not likely to change, it is nearly certain that the number of radios per seat will increase in the future. Be sure to consider the actual duty cycle of each device type when setting the capacity goal. In many cases, it is unlikely that every device will need access to the maximum capacity simultaneously (unless there are specific applications that require it such as interactive learning systems). It's a good idea to use a wireless packet capture utility to study the actual bandwidth requirements of a typical user. Many customers initially overestimate their bandwidth requirements. 18 Capacity Planning for HD-WLANs High-Density Wireless Networks for Auditoriums VRD Solution Guide

19 Step #2: Determine the Usable Number of Channels In any HD WLAN, we need to use as many nonoverlapping RF channels as possible, because data capacity increases linearly with the number of channels. Figure 4 shows two colocated APs on different nonoverlapping channels provide roughly twice the capacity of a single AP. With three APs on different channels in the same room, capacity is roughly tripled. Figure 4 Using Additional Channels to Increase WLAN Capacity Channel A x Channel A x Channel C A A C z w y w v y If one channel provides x Mbps capacity Two APs covering the same area on non-overlapping channels provide 2x Mbps capacity. HD_246 Wi-Fi operates in the 2.4-GHz band and in different segments of the 5-GHz band. The available RF channels are subject to national regulations, but generally there is 83 MHz available at 2.4 GHz and around 460 MHz at 5 GHz. The standard uses 20-MHz or 40-MHz (for n) channels, so standard Wi-Fi equipment is also constrained by these parameters. The number of allowed nonoverlapping channels is the primary capacity constraint on an HD WLAN. For this reason, HD WLANs should always use the 5-GHz band for primary client service because most regulatory domains have many more channels in this band. 20-MHz vs. 40-MHz Channels Most HD WLANs including auditoriums should only use 20-MHz channel widths, also known as HT20. Using high-throughput 40-MHz (HT40) channels reduces the number of radio channels by bonding them together. This forces each AP to serve more users. It is better to have 50 users each on two different HT20 channels than 100 users on one HT40 channel. Also, most handheld devices are not capable of taking full advantage of 40-MHz channels due to their limited processing power single spatial stream radios. HT40 channels are never expected to be used on the 2.4-GHz band for reasons that are beyond the scope of this guide. The main benefit to using HT40 channels is the ability for individual stations to burst at the maximum PHY rate when only a portion of the users are trying to use the WLAN. However, in the auditorium scenario, we must support so many users in a single room that we need every possible channel. In this case, we accept a reduction in the maximum per-station burst rate during light loads in exchange for a greater total user capacity at all times. High-Density Wireless Networks for Auditoriums VRD Solution Guide Capacity Planning for HD-WLANs 19

20 Available 5-GHz Channels The 5-GHz band(s) allow many more nonoverlapping channels than 2.4 GHz. In the United States before 2007, the UNII-I, -II, and III bands allowed the use of a total of thirteen 20-MHz channels (or six 40-MHz channels). The number of available 5-GHz channels varies significantly from country to country. Figure 5 shows the number of 20-MHz channels and 40 MHz channel pairs available for use in the 5-GHz band. Figure 5 5-GHz Nonoverlapping Channels Channels Channels defined defined for 5-GHz for Band 5 GHz (US band Regulations), (US regulations), Showing showing Common common 20-Mhz MHz Channel channel plan Plan and Mhz MHz options Options Channel Frequency (MHz) Band Edg e Band Edg e US UNII-I and UNII-II Bands UNII-I: US UNII I and UNII MHz II bands UNII-II: I: MHz MHz 8x20 UNII MHz II: channels MHz 4x40 8x MHz 20 MHz channels channels UNII-II 4x 40 requires MHz channels DFS UNII II requires DFS Channel Frequency (MHz) Band Edge Band Edg e US Intermediate Band (UNII-II US inextended) rmed ia te band (UNII II extended) MHz 11x MHz channels MHz 5x40 11x MHz 20 MHz channels channels Requires 5x 40 MHz DFSchannels Requires DFS Channel Ba nd Band Edge Edge Frequency (MHz) US UNI-III UNII III // ISM Band band MHz 4x20 20 MHz channels 2x40 40 MHz MHz channels In 2007 the radio regulatory bodies in many countries allowed the use of the UNII-II extended band from 5470 MHz to 5725 MHz as long as UNII-II equipment was capable of Dynamic Frequency Selection (DFS). DFS requires that the AP monitor all RF channels for the presence of radar pulses and switch to a different channel if a radar system is located. Wi-Fi equipment that is DFS-certified can use the extended band, which adds up to another eleven 20-MHz channels or five 40-MHz channels (depending on the radio regulatory rules in each country). 20 Capacity Planning for HD-WLANs High-Density Wireless Networks for Auditoriums VRD Solution Guide