Chapter 3: Environmental Evaluation

The first step in planning the network is to fully understand the environment where you will deploy. The environment is more than the physical structure, which is important, but you also must consider the how the network will be used over time. This chapter describes how to gather the information that will help you successfully deploy a WLAN that meets the needs of the organization.

Network Usage

One of the most difficult questions to answer focuses on how the network will be utilized. Though it is easy to collect a list of common applications and devices that the company supports today, what will the network need to support over its lifetime? After the APs are installed, they typically stay deployed for 4-7 years, and in some networks as long as 10 years. One great example is the decision of whether to use an AP density that is suitable for voice or for data. Many organizations start with a less dense data-only design to save money. But they regret it a few years later when a wireless voice initiative occurs. To plan for the changes to the way the network will be used over time, you must take a lifecycle approach to network design.

The first stop in this process is the IT department because they know what is currently supported. We assume the reader is either part of an IT team or perhaps an outside vendor that supports one. However, you must also consult with managers and business leaders. Often these groups have plans that they have not yet shared with IT that could have fundamental impacts on the network. These new ideas can include completely new services or the shifting of older services from IT-based to cloud-based networks.

You should also consider the quantity and type of new devices that will be coming on to the network due to the bring-your-own-device (BYOD) trend. In the last several years, many organizations have handed out iPads and smartphones to their employees without first consulting the IT department. Of course, employees are already bringing multiple personal devices into the office and expect WLAN access. Consider that the typical “three-screen” office worker has a laptop, personal smartphone, and personal tablet. It’s possible that 66% of the devices that your network has to support aren’t even provided by the organization! As many organizations begin to allow consumer devices on to the corporate network to reduce cost and increase productivity, the device count will only continue to increase.

You must consider these factors when you plan your RF environment. Devices will be roaming more often and the density will be higher. This activity will affect the number of APs that need to be deployed, as well as the choice between single- and dual-band capable devices. Some devices will have multiple radios and transmit chains. Matching AP and device capabilities is required to take full advantage of high-speed data rates. These kinds of changes can be hard to predict, but you must consider them when you build the network to ensure that it will serve the organization well over its useful lifetime.

Determining the Environment Type

The environment type plays a large role in determining how to plan a WLAN deployment. The site conditions drive the choice of planning methodology. Use the following recommendations to help guide the decision of whether to use survey software or a traditional site survey.

Low-Complexity Environments

    Typical environments are open-plan floors with cubicles and a limited numbers of offices and conference rooms.

    Standard deployments primarily consist of APs with integral, omnidirectional or down-tilt antennas deployed at the ceiling level.

    Low-complexity environments typically can be planned using the Aruba VisualRF Plan software and managed via Aruba adaptive radio management (ARM).

    It is strongly recommended that you get a visual inspection of the facility, either in person or with pictures, to identify potential RF obstructions. However, low-complexity environments are often planned virtually with minimal risk.

    If needed, a limited active site survey can be conducted to measure RF propagation in specific areas or other circumstances that warrant relocation of an AP. These adjustments are later entered into VisualRF Plan.

High-Complexity Environments

    High complexity facilities include older construction, hospitals, warehouses, manufacturing plants, airports, aircraft hangars, bus depots, lecture halls, convention centers, historical buildings, and retail stores with floor-to-ceiling shelving. Others are built to withstand natural disasters such as hurricanes and tornadoes. Investigating the use and history of a building can tell you a lot about the need to perform a site survey. Here are some examples:

art    Hospitals and buildings with laboratories or diagnostic imaging suites are complex deployments that require careful examination. The ceiling and wall material can block RF signals (X-ray room walls). Elevator shafts, medical equipment, conduit, and other sources of RF interference can negatively impact the WLAN. In some existing hospitals, a ceiling deployment may not be possible due to the ceiling material type or infection-control requirements.

art    All buildings consisting of older construction materials should be suspect, as they may include asbestos or lead paint (pre-1968 buildings).

art    Buildings with brick or cinderblock walls, or walls covered in plaster should be tested to see to what degree they will attenuate RF transmissions. Concrete walls can have a wide range of different propagation characteristics.

art    Retail store environments and warehouses can vary greatly. Both 2.4 GHz and 5 GHz frequencies can have difficulty penetrating walls, shelving, freezers, containers, and other typical obstructions in a retail setting. Different types of products affect signal more than others. A palette of milk or water will attenuate more signal than a palette of paper towels. Therefore, it is a best practice to perform “active” testing to measure how far signals travel at the desired frequencies.

    Any facility that you think will require external, directional antennas is automatically a complex deployment.

    Factory floors and other buildings with large amounts of metal machinery, especially robotic machinery that is in motion, certainly require onsite inspection and might benefit from an active survey.

    High-density deployments, such as lecture halls and auditoriums, require special attention. If you have a high-density deployment planed, consult the VRD for these deployments at http://www.arubanetworks.com/vrd.

    VisualRF Plan should be used to generate a basic foundation for planning, but it does not replace a physical site survey in these environments. These complex environments require an onsite survey to complete the planning. It is recommended to use VisualRF Plan in these situations only to estimate the AP count and placement to save time during testing.

Wireless RF Coverage Considerations and Questionnaire

Answers to these questions help you to determine the proper Aruba AP type, prepare for the site survey, and plan appropriately for the deployment.

    What 802.11 PHY types are required over the course of the WLAN lifecycle (802.11a/b/g/n)? Without a very good reason, it is safest to assume that 802.11n will be required.

    Which RF bands will be used (2.4 GHz, 5 GHz)? Without a very good reason, always plan to use both bands due to increases in client density.

    What channel width (20 MHz vs. 40 MHz) will be used in each band? Typically 20 MHz channels are used in 2.4 GHz, and 40 MHz channels are used in the 5 GHz band. In dense deployments, speed may be traded off for capacity in the 5 GHz band by reducing to a 20 MHz channel.

    Will voice over Wi-Fi be used? This answer will affect your planning for roaming and AP signal strength calculations.

    Will multicast video over Wi-Fi be used? Use of roaming video has a similar effect as voice.

    Will real-time location services (RTLS) be used? Consider deploying AMs around the building perimeter to help with location accuracy. This deployment ensures that all clients are within the triangulation zone.

    What is the minimum desired PHY-layer data traffic rate that must be available throughout the coverage area? Do some areas have different minimum data rate needs?

    What are the desired air monitoring rates? Are dedicated air monitors required for security or compliance purposes?

    How many devices will each user have? Today Aruba recommends that you plan for at least three devices per user: a laptop, a tablet, and a smartphone. The number of devices per user also has ramifications in the design of VLANs and subnets. Consider if all devices will be active simultaneously, which also impacts AP density.

    What is the maximum number of devices desired for each AP? Typically Aruba recommends 20-30 devices per radio (40-60 per dual-radio AP). This number may be more or less depending on traffic type (voice or data), offered load, and connection type (802.11a, b, g, or n).

    What applications will be in use at the site, both presently and in the future? Bandwidth requirements help determine coverage vs. capacity requirements.

    Are any floor plan images available? VisualRF Plan supports direct importation of JPEG, GIF, PNG, PDF, and CAD (.dwg and .dwf) files for floor plan formats.

    What is the maximum transmit power of the least-capable common device in the network?

    How many transmit, receive, and special streams do the most common devices support?

    If DFS channels are being considered, do the devices most commonly used in the network support DFS channels?

Determining the Deployment Model

It is critical that you select the correct deployment model based on the needs of the organization. There are three common indoor deployment models. The two models covered in this guide are based on capacity and coverage. The third model, high-density design, is covered in a separate VRD, High-Density Wireless Networks for Auditoriums.

In the cases described in this guide, Aruba recommends that you use adaptive radio management (ARM) to maintain channel and power settings and that you maximize client connectivity in the deployment. ARM is covered in the Aruba 802.11n Networks VRD, which is available with all of the VRD guides at http://www.arubanetworks.com/vrd.

Coverage vs. Capacity

Until the last few years, most wireless networks were deployed using a “coverage model” design. In a coverage model, the wireless designer uses fewer APs and tries to get as much range out of each one as possible. As a result, the average data rate delivered at ground level by the wireless network could be very low because those rates are able to travel the farthest due to some basic properties of radio communication. A low data rate in 2.4 GHz 802.11n is 7.2 Mb/s at the cell edges. This model worked well in the past because client devices required relatively low bandwidth for simple data applications.

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Figure 3   Coverage and capacity

However, since approximately 2008, most new enterprise wireless LANs have been deployed using a “capacity model” approach. In this case, we use many more APs because our concern is ensuring that a minimum speed is available throughout the coverage area.

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Today, data and voice designs use a capacity approach. The primary difference between them is the choice of minimum data rate. Data-only deployments have less rigorous needs than voice deployments. For a full explanation of the data rates available see the Aruba 802.11n Networks VRD.

Capacity Model (High Bandwidth)

The capacity model is for dense deployments with high device counts and traffic rates. A capacity-based deployment might consist of APs placed roughly 45 to 60 feet (approx. 13.75 to 18.25 meters) apart running at 25-50% or 50-75% of power. In general, the transmit power of the AP should be set to match that of the least-capable device in the network. If the requirement is a “desk-top like” experience for employee laptops, where the employee can run multiple applications simultaneously, the site requires a capacity-based deployment. Aruba recommends capacity-based deployment for all office and education settings.

Coverage Model (Low Bandwidth)

The coverage model is for low-bandwidth deployments, coverage is required for applications such as a scanner solution or limited guest access. A coverage-based deployment might consist of APs placed roughly 70 to as much as 200 feet (approx. 30.5 to 61 meters) apart in an open space, running at 50-75% of power. If redundancy is not required, APs can run at 100% power, but this typically is not recommended. As an example, if the determined application is a scanning solution with minimal traffic, the site might be a good candidate for a coverage-based model. This deployment would consist of an AP installation base with clients that associate at greater distances and at lower traffic rates. This coverage model would mandate a ceiling deployment.

Aruba no longer recommends coverage-based deployments as networks that had very few clients previously are now seeing new services deployed.

Other Models

Two other models exist that are not covered in this guide: high-density and outdoor deployments. High-density deployments include large spaces where many devices will be present, such as lecture halls, libraries, and stadiums. Outdoor deployments cover a range of deployments including metro-mesh and point-to-point bridging. For both of these models, Aruba has published VRDs that are available on our public website at http://www.arubanetworks.com/vrd.

Ceiling or Wall Mounting

Indoor APs are typically deployed in one of two fashions: ceiling or wall mounted. Aruba recommends against desk or cubicle mounts. These locations typically do not allow for a clear line-of-sight throughout the coverage area, which in turn can reduce WLAN performance.

    Ceiling deployments: The majority of modern WLAN deployments are at the ceiling level. A ceiling deployment can occur at or below the level of the ceiling material. In general, it is not recommended to mount APs above any type of ceiling material, especially suspended or “false” ceilings. There are two good reasons for this. First, many ceiling tiles contain materials or metallic backing that can greatly reduce signal quality. The second reason is that the space above the ceiling is full of fixtures, air conditioning ducts, pipes, conduits, and other normal mechanical items. These items directly obstruct signal and can harm the user experience.

    Wall deployments: Wall deployments are not as common as ceiling deployments, but are often found in hotels and dormitory rooms. Walls are a common deployment location for large spaces such as lecture halls because reaching the ceiling is difficult. Wall deployments may also be preferable in areas with a hard ceiling where cabling cannot be run. If you are not using the Aruba AP-93H, which was designed for wall mounting, consider the antenna pattern before you deploy wall-mounted APs.

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A third mounting option is a “pico cell” design with the APs mounted below floor level. This design is used as part of a high-density network, and is covered in the High-Density Wireless Networks for Auditoriums VRD.

Upgrading from an Existing 802.11abg Network to 802.11n

The vast majority of customers that deployed wireless LANs based on 802.11a/b/g technologies are currently going through a refresh cycle to transition to 802.11n. One of the most common questions Aruba receives is “why can’t I just replace all of my existing APs with new APs?”. The answer is that it depends on the original AP density and the types of applications and devices that are expected to use the new network. This section describes the pros and cons of various upgrade methodologies.

1-for-1 AP Replacement

In a 1-for-1 AP replacement scenario, the older 802.11a/b/g APs are replaced with an 802.11n AP with no changes to AP quantity or placement. The problem with this model is that often the legacy deployment was designed in a coverage model based on 2.4 GHz. Because 2.4 GHz signals travel approximately twice as far as 5 GHz signals, this model is unsuitable for deploying a 5 GHz network. The resulting network will have “islands” of 5 GHz coverage and slower client connections on that band. Without complete 5 GHz coverage, advanced ARM tools such as band steering cannot be as effective at moving clients. Networks deployed with 802.11n in this model should expect the roughly the same performance at the AP coverage edge as their legacy network.

When a 1-for-1 AP replacement is proposed, Aruba recommends that a new, virtual survey be performed with VisualRF Plan and compared with the current deployment. The new survey provides a comparison of the current deployment to a more optimal 802.11n network in the same space. To determine if 1-for-1 replacement is viable, see the flowchart in Figure 4. A new plan may be required.

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Figure 4   AP location reuse decision tree

Mixing 802.11n and 802.11a/b/g APs

In some deployments, 802.11n APs will be rolled out in phases. In the past, some organizations have chosen to deploy mixed environments with the newer 802.11n APs mixed with legacy 802.11 a/b/g APs.

Aruba strongly recommends against this practice because numerous issues with client behavior related to device roaming have been observed.

As most clients move through the network, they expect to see the same channel width and modulation types in use. Roaming from an 802.11n 40 MHz channel to an 802.11a 20 MHz channel causes some devices to become “stuck” to the higher speed AP. In some cases, devices disconnect themselves from the network, which requires manual intervention by the user.

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Figure 5   Mixing 802.11a/b/g and 802.11n APs

When you must take a phased approach to 802.11n deployment, Aruba recommends that you completely upgrade one floor or building at a time with new APs. This approach gives devices in that area the best chance of remaining connected to the network and provides a better user experience.

Multi-floor Deployments

In a building with multiple floors, the network engineer must stagger APs both on the floor and between floors. If APs are installed in a line directly above one another, ARM will reduce power to limit co-channel interference (CCI) and adjacent channel interference (ACI). The reduced power means reduced coverage. (See Figure 6.)

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Figure 6   APs installed in a line above one another

Aruba recommends that you stagger the location of APs so that APs on adjacent floors are not vertically aligned with one another, in a three dimensional checkerboard pattern. (See Figure 7.)

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Figure 7   Staggering APs between floors

Hallway Deployments

Deployments that have APs located down the length of a hallway are often found in hotels and dormitory rooms. The idea behind this method is that the APs in the hallway can provide coverage to rooms on either side of the hallway. These APs are often placed physically close to one another due to the density of the rooms.

However, this type of deployment usually creates a lot of problems and dissatisfied users. One reason is that the hallway building materials absorb significant signal, which results in poor in-room performance. Another problem is that the APs have clear line-of-site to one another, which increases co-channel interference (CCI) and adjacent-channel interference (ACI), which results in lower throughput for users. Similar to the multi-floor deployment, the hallways are stacked vertically. This arrangement leads to additional multi-floor interference as described in the previous section. This interference causes ARM to reduce power, which exacerbates the coverage challenge in the rooms. (See Figure 8.)

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Figure 8   APs in a hallway deployment

Instead of trying to use hallway APs at high power to cover users through a wall, Aruba recommends using many room APs at low power to cover the user space directly. Depending on how much attenuation the building presents, you will put an AP in every 1, 2, or 3 rooms. You will stagger APs inside of rooms on either side of the hallway and vertically. On one floor, install an AP in every other room, and APs should not be placed in rooms directly across the hall from one another. (See Figure 9.)

In addition, from a three-dimensional perspective, Aruba recommends that you also stagger APs vertically. On the next floor, place the APs in the same manner, but the rooms should be reversed. So, the room on floor 1 that has an AP does not have an AP on floor 2, and so on. Depending on deployment requirements, the AP-93H wall box AP can be a good solution for this deployment model. Place the APs against the back wall and point them toward the hallway.

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Figure 9   APs deployed in rooms