High-Density Wi-Fi. Application Note

Transcription

1 High-Density Wi-Fi Application Note

2 Table of Contents Background... 3 Description... 3 Theory of Operation... 3 Application Examples... Tips and Recommendations

3 Background One of the biggest challenges faced by 802. networks is dealing with high-density user deployments. Wi-Fi was initially intended to provide LAN access for a moderate number of users. The evolution and overwhelming success of this technology has brought 802. deployments to environments that go well beyond a few users to a point where it can now be the primary access to the LAN. It is not difficult to find Wi-Fi networks deployed across campuses, industrial areas, and even municipalities offering a wide variety of services. In these networks, it is often seen that the number of users connected to the network surpasses the initial design considerations and as a result, performance no longer meets expectations. Description This Application Note presents Xirrus solution for providing high quality network access for high user densities over a Wi-Fi infrastructure. Traditional or 2 radio APs have proven inadequate in handling such environments. Truly successful high-density deployment requires Wi-Fi equipment that is designed with scalability and performance in mind. There are a number of design elements in Xirrus Wi-Fi Arrays that make them uniquely powerful for high-density networks. These innovations include, but are not limited to: Multi-radio System (IEEE 802.a, IEEE802.b, IEEE 802.g and 802.n): Xirrus Wi-Fi Arrays incorporate 4, 8, 2, or radios into a single device. Each radio can be assigned to a unique channel providing dedicated bandwidth. Antenna Sectorization: Directional, high gain antennas in a sectored Array design provide a key capability for channel re-use in confined environments. Auto Cell Sizing: Automatic control of power and sensitivity per radio allow control of the size and performance of the coverage area. Station Load Balancing and Association Limits: Appropriate distribution of users among radios is key for high-density without requiring modifications to the Wi-Fi client and avoid radio overloading. Traffic Shaping: Controlling user traffic prevents any one station from clogging the network. Broadcast /Multicast Control and Station Privacy: Broadcast/multicast traffic can extract a large toll on any network, so minimizing its effect improves network performance. Radio Monitoring: Spectrum Analysis is an important troubleshooting aid. Theory of Operation Among the many challenges found in high-density Wi-Fi environments, the one that can be most difficult is channel reutilization. The best way to provide bandwidth to a high number of simultaneous users is to leverage as much of the RF spectrum available to Wi-Fi as possible and as many times as possible. This means a multi-radio with intelligent antenna design to use as many separate channels as possible while avoiding co-channel interference. The following sections explain how the Xirrus Wi-Fi Arrays can create high-density user networks. 3

4 Multi-Radio System Perhaps the most intuitive assumption is that in order to provide the best throughput to Wi-Fi clients, the connection between the client and the access point (AP) must be established at the maximum possible data rate (also known as link rate). In the case of 802.a and 802.g, the data rates will be 54Mbps, and with 802.b, it is Mbps. The new 802.n standard takes data rates up to 00Mbps. The table below summarizes the current 802. technologies. 802.b/g 802.a 802.n Band 2.4GHz 5 GHz 2.4 GHz, 5GHz Channels,2,3,4,5,,7,8,9, 0,,2,3,4 Number of nonoverlapping channels 3,40,44,48,52,5 0,4,00,04,08, 2,,20,24 28,32,3,40 49,53,57,,5 Same channels as 802.g and 802.a non bonding 3 with bonding Channel Width 20MHz 20MHz 20MHz and 40MHz Max Data Rate Mbps / 54Mbps 54Mbps 288/00Mbps Table The data rate is a function of the signal quality that is affected by distance and the noise levels generated by nearby Wi-Fi or other interference sources. A high error rate will force clients and APs to negotiate lower data rate connections even if the signal level is strong enough to support higher data rates. The actual throughput a user can achieve is a function of Free Air Time, which is the time the media is available for the client to transmit or receive. The access to the media is controlled by the CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) algorithm. When the client detects energy in the media due to other transmissions, certain levels of noise and interference or adjacent channel emissions, the client must wait until the media becomes free. If the media is only available half the time for a particular client, the maximum throughput that client can transmit or receive will be half as well. This brings the concept of Available Capacity, which is the product of the Free Air Time and the data rate between the AP and client. The best method to increase the Available Capacity is to provide the highest data rate and maximum Free Air Time. The use of more spectrum and more radio channels increases airtime availability. When clients are able to associate to multiple APs operating on separate non-overlapping channels, then simultaneous transmission can occur, thereby increasing overall throughput and system capacity. The Free Air Time increases proportionally to the number of channels that are being used. The higher the number of non-overlapping channels used in a particular area, the more Available Capacity for that area. 4

5 Free Air Time is also related to the data rate of the links between APs and clients. The higher the data rate, the less time the media will be used to transmit a given amount of information. A user transmitting a 500byte packet at Mbps will be using the media (airtime) 54 times longer than a user transmitting the same 500byte packet at 54Mbps. The Free Air Time also depends on the number of clients in a channel. For a particular traffic pattern and data rate per client, Free Air Time linearly decreases with the number of clients present in a particular channel. In summary, in order to increase the highest data rate and maximum Free Air Time, one should simultaneously use multiple channels (radios) per system and reduce the number of users per channel. The Xirrus Wi-Fi Array does this and goes even further with antenna sectorization allowing for smaller coverage areas (small cells), guaranteeing higher data rates and channel reuse to provide the best combination for better overall Wi-Fi Available Capacity. Antenna Sectorization Appropriate planning of coverage areas is another critical task when deploying high-density wireless networks. The coverage area correlates to the maximum distance clients can be from a given AP with enough signal to associate and operate at a usable data rate. Data rates within the cell will vary depending on the actual distance clients are from the AP. In the previous section, it was mentioned how the use of multiple channels and radios allows a greater number of stations in a given area and thus provides greater capacity. In high-density environments, the number of stations per channel might be too large for the AP to provide adequate throughput. In these cases, the Wi-Fi network must re-use the same channels several times within a given area by creating smaller or sectorized coverage areas. This approach is similar to the one cellular carriers use for mobile phones. By creating a larger number of smaller cells, it is possible to achieve greater density, resulting in increased capacity. Because these cells are smaller, the number of users per channel can be limited and provide additional re-use of channels at much closer distance. The choice of omni-directional or directional antenna design will also have a significant impact in the re-use of channels. The use of sectorized directional antennas presents several advantages over omni-directional antennas: Allows the use of several channels in the same AP system, minimizing co-channel interference. Allows better-defined cells by concentrating energy in a sector. Limits the amount of interference received from other directions thus reducing packet errors. Improves receive sensitivity in the direction of the cell since antenna gains work in both directions. Reduces multipath issues because RF is not blindly transmitted in all directions. Helps in hidden node problems. In Figure, there is an area where three non-overlapping channels are used with omni-directional antennas. The black dots represent 30 wireless stations inside a cell. The closest available channel for those stations will be channel. The distance required to reuse channel again within the coverage area is shown. 5

6 Figure Figure 2 Figure 2 shows the coverage provided using sectorized antennas using additional radios per system. For the same station, there are now three channels covering the same area resulting in greater distribution of stations only 0 stations share a channel. By tripling the density of radios per system and using sectorized antennas, the available capacity of the area has been increased by a factor of three. This scenario can be further improved by adding more radios per system. Since the number of non-overlapping channels in the 2.4GHz band is only three, the recommendation is to add radios in the 5GHz band. Figure 3 shows an example of a Xirrus Array sectorizing channels in one cell and Figure 4 shows 2 channels in one cell. Figure 3 Figure 4 Auto Cell Sizing The size of the cell or coverage areas is determined by the transmit power and receive sensitivity of both the AP and the stations. By tuning those values, the cell size can be adjusted to accommodate the dimensions and client density requirements. Adequate power control is also important to mitigate the interference between radios operating in the same channel. Xirrus Arrays have the option to either set the cell sizes manually or automatically via the Auto Cell feature. Auto Cell is an automatic, self-tuning mechanism that balances cell size between Arrays to guarantee coverage while limiting the RF energy that could extend beyond the organizational boundary. This is accomplished by setting radio power dynamically so that complete coverage is

7 provided to all areas, yet at the minimum power level required to diminish potential interference with neighboring networks. Additionally, Arrays running Auto Cell can detect and compensate for coverage gaps caused by system interruptions. Several Auto Cell parameters can be defined including minimum cell size, scheduled RF assessment/adjustment, and the ability to define a coverage overlap percentage for roaming. An overlap of 5% to 20% between cells is recommended for seamless roaming. Without Auto Cell Figure 5. Without Auto Cell Figure 5 shows that when two radios are operating, stations B and C could potentially experience interference from neighboring Arrays and 2 resulting in corrupted packets. Strong co-channel interference could cause stations in adjacent cells (cells and 3) to defer communication while stations in cell 2 are transmitting, resulting in the reduction of overall throughput. In the event of Array 2 failure, stations A and D could lose all connectivity. With Auto Cell Client A Client A Array 2 Array 2 Array Client B Client C Array 3 Array Client B Client C Array 3 Client D Client D Figure. Without Auto Cell In Figure above, Array radios balance power levels between themselves to guarantee client coverage, but without the potential of interfering with other cells. In the event of Array 2 failure, Arrays and 3 automatically detect the loss of energy from Array 2 and raise their own radio power levels to compensate for the loss. Stations who were on Array 2 then re-associate to the other Arrays. 7

8 In the case of manually configuring the cell sizes, the Xirrus Arrays have predetermined cell sizes for different applications. In the case of high-density environments where channel re-use is definitely required, medium or small cell sizes should be used. Table 2 below shows the values of TX power and RX sensitivity for different cell sizes. Cell Size Transmit Power (dbm) Receive Sensitivity (dbm) Small 5-75 Medium 2-8 Large 9-87 Max (Default) Auto AutoCell AutoCell Manual to dbm to -5 dbm Table 2. Power and Receive Sensitivity settings on Array Other combinations of values with more granularity can be manually configured to accommodate other deployment requirements. Station Load Balancing Load Balancing allows the Array to distribute stations among all available radios in an area with the goal of providing maximum bandwidth to all stations. By moving a station from one congested radio to a less congested radio, load balancing allows that station to have more available bandwidth. Additionally, it also decongests the radio where the station was initially connected allowing the remaining stations on that radio greater overall bandwidth. This is very important as described in the first point of this section where the available capacity linearly decreases with the number of stations on a channel. The Xirrus Wi-Fi Array supports automatic Load Balancing to distribute Wi-Fi stations across multiple radios. In 802., it is the station that decides to which radio it will associate. The Array cannot actually force station association to a specific radio, however the Array can encourage stations to associate in a more uniform fashion across all of the radios of the Array. In high-density environments where the stations are uniformly distributed within the coverage area, it would be expected that the load distribution among radios would be also uniform. This is not always the case. Typically the station will connect to the AP that has the strongest signal strength, but when the station moves to another location, it may remain connected to the previous radio until the signal drops below a certain threshold. Stations that are constantly moving can create inconsistent load distribution conditions. Another case of inconsistent distribution occurs when many stations move into a concentrated space such as meeting rooms, conferences or auditoriums. In this case, the strongest signal level for those stations may come from one particular radio and all those users will associate to that radio leaving other radios in the vicinity lightly loaded. The Array decides if a particular radio is over utilized and should not allow any more associations. This decision process is based on a load-balancing algorithm that takes 3 key factors into affect: Fewer stations on a radio is preferable The strength of the signal 8

9 5GHz channels preferred over 2.4GHz channels Station Limits To Load Balancing stations, the Arrays have the option to limit the number of associations per radio. When the number of associations reaches the configured limit, the radio sends the station a message indicating that the radio has reached its limit, encouraging the stations to associate to another radio. Traffic Shaping 802. is a shared medium. In a high-density Wi-Fi environment, traffic shaping is recommended to optimize or guarantee performance levels. It is commonly applied at the network edges to control traffic entering the network. Traffic shaping causes additional delays by serving queues more slowly than if traffic shaping was not applied. Xirrus has incorporated different traffic shaping methods such as: Traffic Classification: Support for WMM /IEE802.e (Quality of Service) Rate Limiting: To control the maximum rate at which traffic is sent Traffic classification can be configured on Xirrus Wi-Fi Arrays to provide traffic prioritization for delay sensitive applications such as voice and video. Rate limiting can be configured on the Array per SSID or User Group in the following ways: Traffic overall Traffic per station Broadcast and Multicast Control Unnecessary broadcast and multicast packets are a type of traffic that is undesirable in Wi-Fi networks. The reason broadcast and multicast traffic packets are so detrimental is because those packets are sent at the lowest basic data rates. Because these packets are intended to reach multiple stations that might be located at different distances, only the lowest data rate can guarantee reception to all of them. As mentioned, low data rate transmissions require more time to send the same amount of information. To optimize performance in high-density environments, it is important to minimize the amount of unnecessary broadcast and multicast traffic. Both types of traffic are typically required and cannot be eliminated, but the amount of this type of traffic transmitted over the air needs to be controlled. Xirrus Wi-Fi Arrays incorporate several features to control broadcast/multicast traffic in the air: ARP Filtering: Address Resolution Protocol finds the MAC address of a device with a given IP address by sending out a broadcast message requesting this information. ARP filtering allows the proliferation of ARP messages to be reduced by restricting how they are forwarded across the network. The following are options for handling ARP requests: o Off: ARP filtering is disabled and requests are broadcasted to stations. This is the default value. o Pass-thru: The Array forwards the ARP request. It passes along only ARP messages that are associated to the target the stations. o Proxy: The Array replies on behalf of the stations to which it is associated. The ARP request is not broadcasted to the stations. 9

10 Broadcast/Multicast Optimization: o Broadcast/Multicast Optimization: Restricts all broadcast/multicast packets to only those radios that need to forward them. For instance, if a broadcast comes in from VLAN 0, and there are no VLAN 0 users on a radio, then that radio will not send out that broadcast. This increases available airtime for other traffic. o Rate Optimization: Changes the rates of broadcast traffic sent by the Array (including beacons). When set to Optimized, each broadcast or multicast packet that is transmitted on each radio is sent at the lowest transmit rate used by any station associated to that radio at that time. This results in each IAP broadcasting at the highest Array TX data rate that can be heard by all associated stations, thus improving system performance. The rate is determined dynamically to ensure the best broadcast/multicast performance possible. The benefit is dramatic; consider a properly designed network (one that has -70db or better everywhere), where virtually every station should have a 54Mbps connection. In this case, broadcasts and multicasts will all go out at 54Mbps vs. the standard rate. This means that with the broadcast rate optimization on, broadcasts and multicasts use between 2% and 0% of the bandwidth that they would in Standard mode. When set to standard (default), broadcasts are sent out at the lowest basic rate only Mbps for 5GHz stations, or Mbps for 2.4GHz stations. In addition to those features, traffic filters can be created to limit or block any other type of traffic that is not necessary or is slowing down the air portion of the network. Station-to-Station Blocking Station-to-station blocking prevents stations connected to the same Array from sending traffic directly to each other. As a result, only traffic to/from the wired network is allowed. This feature provides multiple benefits. First, it improves security since it prevents users from accessing other devices on the network without the need to implement firewalling or filtering. Second, it helps optimize broadcast and multicast traffic in the air. Broadcast traffic sent by a station will not be sent back to the air by the other radios in that Array. Since broadcasts are sent at the lowest data rates, this helps increase the overall available air time. Station-to-station blocking may also be enabled in the network switches where the Arrays are connected; this will prevent stations from communicating with each other when associated to different Arrays. Radio Monitoring Spectrum Analyzers are used for troubleshooting Wi-Fi networks as well as for spectrum analysis. There are numerous devices including microwave ovens, cordless phones, and Bluetooth devices that can cause RF interference and degrade the performance of an 802. Wi- Fi network. Often the sources of interference are signals from nearby Wi-Fi networks and can be located with the use of a spectrum analyzer. There is an integrated Spectrum Analyzer function (Figure 8) in every Xirrus Wi-Fi Array that allows network administrators to monitor and troubleshoot their wireless networks in both 2.4GHz and 5GHz spectrum in a distributed manner. They are mostly used to detect existing sources of interference. 0

11 Figure 8. Radio Monitoring Using the Spectrum Analyzer on the Array provides users with the following real-time statistics in each and every channel in the 2.4GHz and 5 GHz band. Packets/ sec: Total number of packet per second Bytes/sec: Total number of Bytes per second 802. Busy: % of time that 802. traffic is seen on that channel Other Busy: % of time that non-802. traffic is seen on that channel Signal to Noise: Average Signal to Noise Ratio Noise Floor: Average noise floor seen on that channel Error Rate: % of 802. packet with CRC errors Average RSSI: Average RSSI level seen on 802. packets Average Data Rate: Average Data Rate over time Application Examples This section shows two real-world examples of high-density environments that have been deployed using Xirrus Wi-Fi Arrays. In these examples the configuration guidelines are outlined for the important Xirrus features discussed previously. For additional details and how to configure these features, please refer to the Xirrus Array User Guide as well as documents that are available on the Xirrus website. College Classroom/Auditorium A large college classroom or auditorium is a typical case of a high-density environment. In such applications, laptop-to-student ratio can reach : when all students are required to have a laptop to access online or school resources during class. In this example, the design goal was to provide wireless access to 40 simultaneous students in a lecture hall. Only one Xirrus Wi-Fi Array, model XS8, was deployed. On this 8 radio Array, 3 were deployed at 2.4GHz, 4 at 5GHz, and one as a dual band monitor radio. It is important to note that the monitor radio can also be used as a regular access radio in case additional capacity is required.

12 A ratio of 20 wireless stations per radio is used in this deployment, which represents a good balance for bandwidth and coverage. Within the coverage area, the expected signal level is sufficient to guarantee the highest possible data rates. The most important Array features for this scenario are multi-radio, sectorization and load balancing. Network Topology The topology in this example is very simple. Just one Array was deployed and powered through PoE and installed hanging from the ceiling in the center of the facility as shown in Figure 9. Figure 9. Lecture hall Configuration Channel Plan: The Array is configured for Auto Channel selection. After scanning the area, the Array will select the most optimal channels in which to operate. Since three of the 2.4GHz radios are enabled, the Array will pick channels,, and. For the 5GHz, the Array will select four channels taking into consideration outside RF interference conditions. The eighth radio is typically used in a threat sensor mode. Cell Size: Although Auto Cell is not relevant when deploying only one Array, it should be considered in case other Arrays are deployed within the vicinity, such as in other classrooms. The cell sizes of each radio in the Wi-Fi Array can be customized. In Figure 0 below, each radio is set to a different cell size for illustration purposes. However, in most implementations, all the radios are set to similar cell size. When configuring cell size manually, the cell size can be set as small, medium, large, max, or manual. 2

13 Figure 0. Auto Cell Please refer to the AutoCell Application Note for additional configuration details. Load Balancing Having the stations homogenously distributed on the Array is very important to offer maximum bandwidth. There are three possible settings for Load Balancing: Off: Load balancing is disabled. On: The overloaded radio will ignore Probe Requests for a few seconds expecting that the station will go to another radio. During that time, the radio will still respond to Association and Authentication Requests (i.e. if the station already knows the radio is there). After a few seconds if the station keeps sending Probe Requests, the radio will start responding admit access. Aggressive: In this case, if a radio is overloaded it will ignore all Probe Requests, Association Requests, and Authorization Requests from additional stations. It will do this indefinitely until its load decreases. This way the Array makes sure the users have associated to other radios less congested. Please refer to the Station Load Balancing Application Note for configuration details. Station Limits If Load Balancing is not used, another possibility is to set a station limit. When a radio reaches the established limit it will not accept connection from additional stations. Traffic Shaping The type of applications that will be accessed during class will determine the amount of allowed traffic per user. Traffic shaping should be enabled to prevent students from utilizing more bandwidth than necessary for the purpose of the class or to from transferring large amounts of information between them. The traffic limitation can be enabled on per SSID or per user group. Per SSID o At SSIDs >SSID Management, select the SSID that rate limiting is to be configured. User can choose to configure either one or both of the following: - Uncheck Unlimited and enter a value for the overall traffic for the selected SSID. - Uncheck Unlimited and enter a value for maximum rate allow for each station associated to the selected SSID. 3

14 Figure. Traffic Shaping Per SSID Per User Group o At Groups >Group Management, select the Group that rate limiting is to be configured. User can choose to configure either one or both of the following: - Uncheck Unlimited and enter a value for the overall traffic for the selected Group - Uncheck Unlimited and enter a value for maximum rate allow for each station in that Group. Figure 2. Traffic Shaping Per User Group Broadcast and Multicast Control ARP filtering should be set to Pass-thru or Proxy. To control of ARP traffic with Proxy and Pass-through mode Figure 3. ARP Filtering Station-to-Station Blocking Go to IAPs > Global Settings to enable/disable intra-station traffic Figure 4. Station-to-Station Blocking This feature was not enabled at the above example. Radio Monitoring As mentioned before, the monitor radio can be also used as a regular access radio. In this example, the number of radios available in the Arrays is sufficient to accommodate the number of students, so the monitor radio is used for spectrum analysis and intrusion detection. In order for the spectrum analyzer to function, there are 2 things that needs to be enabled on the Array: 4

15 The abg2 (XS series) or abgn2 (XN series) IAP must be configured as a monitor using the omni-directional antenna. Intrusion Detection Mode must be set to Standard. Go to IAPs > IAP Settings, configure abg2/abgn2 as monitor Figure 5. Radio Monitoring At IAPs> Advanced RF Settings, select Standard mode for Intrusion Detection Figure. Intrusion Detection In RF Monitor >Spectrum Analyzer, an overview of the 802. and non-802. activity in both 2.4GHz and 5GHz channels can be monitored. Convention Center A convention center is a perfect example of a high user density wireless environment. In this case, high-speed wireless Internet access is provided to 7000 attendees with approximately 3000 simultaneous users in a 50,000 square-foot hall. Various types of applications are supported including web access, , corporate VPN, text messaging, and VoIP stations connecting in both the 2.4GHz and 5GHz bands. Network Topology The area is covered using twelve Xirrus Wi-Fi XS Arrays. The XS Array includes twelve 802.a, three 802.bg and one monitor spectrum/analyzer radio. The physical distribution of Arrays within the area is mostly uniform with half of the Arrays standing on tripods along the perimeter of the hall and the other half hanging from the ceiling. In this configuration (Figure 7), a total of 80 radios are available 3 operating in 2.4GHz proving 802.bg access and 44 operating in 5GHz providing 802.a access. 5

16 Figure 7. Array Deployment with Channel Allocation All Arrays are wired to GigE switch ports and powered via PoE. Configuration Channel Plan: In such an environment with a high density of radios, close proximity between Arrays, and no considerable obstructions between them, the channels can be easily assigned manually. Twelve 5GHz channels and three 2.4GHz channels are used for a total of 5 per Array. For the 2.4GHz band, only three non-overlapping channels in the US regulatory domain are used:, and. In the 5 GHz band, if the UN-II band channels are not considered, there are a total of 3 non-overlapping channels to allocate to 2 radios. The channels are set manually, replicating the same channel plan on all the Arrays and placing each Array in the same orientation (rotation). Cell Size: Considering the distance between Arrays and a static and controlled environment, the cells size are set to medium because the average distance from station to Array is relatively short. Channel interference between Arrays will determine the cell size rather than the size of the coverage area or required data rate. Load Balancing: This feature is enabled in all the Arrays and set as normal. The behavior of the users should be monitored at peak time and if the distribution does not look uniform, Load Balancing may be set to aggressive. Consider that in this environment, users are free to move and they could be creating areas of higher density than others. Traffic Shaping: In this particular deployment, traffic shaping was set to 2000 packets per second per user. Other traffic limitations can be set depending on the network requirements, for example applying filters to limit application support.

17 Broadcast Control: ARP filtering is set to proxy and station-to-station blocking is enabled. In this example, these two features are more critical since the amount of stations in the same broadcast domain is much higher than in the previous example. Tips and Recommendations High user density environments can push Wi-Fi networks to their limits, largely based on the contention created by many stations accessing a shared communication medium. The most important capabilities of the Xirrus Wi-Fi solution to enable successful deployment in such environments are its multi radio/multi-channel design, antenna sectorization, load balancing, and broadcast control. Beyond these facilities, the following recommendations may be used to optimize these types of deployments: Monitor the number of users per radio and radio utilization during peak times using the XMS to understand the user distribution. Enable aggressive load balancing if necessary. Monitor that the radios in all Arrays are functional and reporting information for future data collection and statistics generation. In cases where access for legacy 802.b stations is not required, configure the Arrays for 802.g only. This will eliminate the lowest data rates from the air and improve the overall performance on those radios for 802.g stations. Analyze the type of traffic that is being sent by the stations using a packet sniffer. If certain traffic types are seen that are not desired and can be eliminated (e.g. video streaming, P2P, etc.), create filters in the Arrays to block them. Implement station-to-station blocking on the switches to which the Arrays are connected to prevent users on different Arrays from communicating with each other. Monitor the backhaul and WAN utilization of the network to understand the traffic flow and magnitude to ensure these components of the network are not becoming a bottleneck. Use the XMS to monitor the traffic utilization of each Array to see if some are carrying more traffic than others or have many more users associated to them. Use the results to better distribute usage accordingly. For example, a lower user limit can be set in the Arrays that carry more traffic. Look at the traffic statistics and check the number of retransmissions. If a high percentage of retransmissions is detected, there may be too much inter-array interference. In this case, lower the TX power of the Array radios Check the Array IAP and station statistics to understand the number of users connected at low data rates. A lot of traffic at low data rates may indicate users are roaming and not selecting the closest radio. In this case, aggressive load balancing may be enabled and additionally increase the sensitivity threshold. 7