Wireless networks can be designed in a variety of ways. The number and type of components in the network, the way the components are physically and logically connected, along with the method by which the components are controlled is the wireless architecture. As you are designing your wireless network and RFP, deciding on the density of APs and the best controller architecture for your environment are important decisions.
What you will learn:
The number of APs that you need depends on whether you want to design for coverage or for user density and technology usage. In the past, many districts designed their networks and placed APs to fully blanket the buildings with Wi-Fi, but just barely. A single AP would cover multiple classrooms, sometimes up to four or five. Today, with the number of devices and the demand for bandwidth skyrocketing, designs are changing so that the network can accommodate students having up to three devices. To meet today’s demands, APs need to be installed more densely than in the past so that each AP doesn’t get overloaded with too many user devices. The exception to this rule is multi-radio APs, like Xirrus’s arrays. If an AP has more than one radio per band and smart antenna technology to direct and extend the signal, fewer APs are needed.
Many districts have experienced coverage issues when they moved from single band 2.4 GHz APs to dual band APs. Because of its higher frequency, the 5 GHz band has a smaller cell size and does not penetrate walls as well as the 2.4 GHz band. If you are designing for coverage only, you will need slightly more APs if you are moving from a single band to a dual band model. However, if you are designing for density, by design the cell sizes are going to be significantly smaller than in a coverage model so the difference between 2.4 GHz penetration and 5 GHz penetration is no longer a major factor in determining how many APs you need. Instead, your client location, type, and density is what determines the number of APs required.
If your district currently has 1:1 learning or is planning to move to a 1:1 environment within the next 3-5 years, the question on your mind is probably "What type of wireless system do I need to support 1:1?" Luckily, most wireless solutions, if installed with the correct density can support a 1:1 environment.
There is a lot of debate about the correct number of APs per classroom. Many 1:1 districts have installed less than one AP per classroom in a saw tooth pattern and have achieved perfectly acceptable performance. Other districts swear that one AP per classroom is needed to handle their constantly growing bandwidth demands. Ultimately, it all comes down to a good site survey. Without the site survey, which takes all of the variables into consideration (building construction, number of user devices, type of user traffic, interference levels, 802.11n vs 802.11ac, and more), it is difficult to make a blanket statement about how many APs every district in the country needs.
Many districts have found that, with a tight budget, they have had to start with fewer APs to provide coverage instead of density (one AP per every two or three classrooms), and begin to increase density each year as they are able to purchase more APs. This strategy is fine as long as the vendor is aware of this strategy when performing the site survey such that they can suggest an appropriate strategy to add APs each year.
EducationSuperHighway has recommendations (see chart below) about the number of APs per classroom that a typical district may need for high-density Wi-Fi. These recommendations are meant to be used as planning and budgeting guidelines, but they are not intended to replace a good site survey and should not be used as a specification in your RFP otherwise you may end up buying more than you need. Your RFP should require that the vendor perform a site survey and base the design on their results.
A controller-based architecture is a wireless design in which every AP is managed by some type of controller.
Modern wireless networks all implement the concept of centralized control of the APs. The centralized control can be done via a physical controller or a cloud-based controller (for now, let’s say that controller-less and virtual controller systems fall in this category). Physical controller architectures have been around for years and have been proven to be very stable and secure. Cloud-based architectures are newer but have become very popular over the last few years among school districts because of their simplicity. Either are good options for districts of any size.
Physical controller architectures benefit from having somewhat more local control over the user traffic. The controller can process every packet of data, so some administrators consider this design to be more secure and better at providing visibility into the traffic. Also, the physical controller is situated within your district’s network, so you are not relinquishing control of uptime or usage data to the manufacturer hosting the controller.
Cloud-based solutions rely on the manufacturer who is hosting the controller to maintain a high level of uptime. While this was initially a concern for customers, the uptimes have been extraordinary so this argument has become less important over time. The main benefit of cloud-based solutions is their simplicity to install, configure, and maintain. They also tend to have more straightforward purchasing and licensing models.
If you have an existing physical controller infrastructure that you like or if you have controllers that are not yet at their end of life, you may want to take advantage of your existing investment and continue with a physical controller architecture. Or, if you like the added control and security of a physical controller you should consider a physical controller architecture.
If you are not really sure where to start or are looking for a quick and easy solution while still having a straightforward management experience, a cloud-based architecture may be the best approach for you. However, due to high ongoing licensing costs, these solutions may not be an option for districts on an extremely tight budget.
Ideally, you should talk to your vendor to discuss the architectures and their associated price tags might be best for you.
Depending on what you decide, you will still need to make some deeper architecture decisions. Continue to either Which physical controller based architecture is right for you? or Should you consider a controller-less or cloud based controller architecture?
In this architecture, the controller(s) resides at the district office (or any central location) and all of the remote school APs are controlled across the wide area network (WAN). If a district has multiple small schools, a central district office, and a reliable high-speed WAN with low latency, a centralized controller model may be a cost effective design.
In this architecture, controllers reside at each school (or at large schools) rather than centrally at the district office. If a district has large schools or an unreliable WAN this is a smart choice.
Recently "converged access" is becoming more prevalent. This means that the switch acts as a local controller for directly attached APs.
Consider your traffic flows, stability and capacity of WAN, content caching, budget, management capability, and high priority features before choosing a controller architecture.
Every district has very different WAN infrastructure, requirements, and budget so your choice of architectures should take these into consideration. If you have a highly reliable and low latency WAN, you can consider a centralized controller solution because it is easier to manage and less expensive. If you do not have a reliable WAN, you should consider a distributed controller but be aware that this will increase the cost of the network.
Ultimately, it is important to understand that every school district is different. We recommend that you seek input from your vendor before making a decision.
If you have a controller-based architecture with a data plane tunnel from each AP to the controller, the controller will need to have multiple high capacity interfaces to avoid becoming the bottleneck in the wireless network. The traffic from several APs being tunneled to the controller can quickly add up to multiple gigabits of data, so several Gigabit Ethernet (GbE) ports or 10 GbE ports may be necessary.
Split tunneling is a concept in which tunneled traffic flows are split depending on their destination. In the case of a wireless controller architecture, this means that some traffic will traverse the tunnel from the AP to the controller (typically the control plane), while other traffic will stay local and be placed onto the appropriate VLAN at the AP (typically the data plane). This feature is most useful when the controller is installed centrally, but much of the user traffic will stay local, thus avoiding the case where traffic traverses the WAN twice unnecessarily.
Autonomous APs (frequently known as heavy or fat APs) maintain their own individual configuration and do not receive configuration changes from a controller.
Sometimes called the distributed controller architecture, coordinated control functionality (equivalent to what a controller provides) is split up amongst all of the APs. This may sound similar to the standalone architecture, but controller-less systems are much more sophisticated such that the APs work together to create a dynamic network, much like in a controller environment. Though the controller functionality is a part of the AP, these solutions typically use management software to manage and monitor the APs and clients.
There are a limited number of controller-less systems on the market, but the ones that exist are very good and should not be ignored simply because they do not use a controller. Examples of controller-less systems are:
A cloud controller is a controller that is hosted by the manufacturer and your configuration/AP management are all done by logging into your district’s management interface using a web browser.
A virtual controller is controller software that can be installed on any system, either locally or cloud based. This controller does not necessarily have to be available 24/7 to manage the network.
Cloud based controllers are becoming more popular so many manufacturers are starting to release their own cloud product lines. It may take some time for these new products to stabilize, so be sure to check for customer references if you are considering one of the newer products.
Standalone AP architectures are outdated and do not provide nearly the same number of features, functionality, or performance than other types of architectures. No matter how small the wireless installation, it is worth the extra money for the advanced management features that come with the either a controller-less architecture or a cloud-based controller.
The differences between the controller-less and cloud-based controller systems are all "under the hood" so users and administrators will generally not be able to tell the difference between the two. Both of these designs are good options for districts of any size. They are straightforward to design, install, manage, and monitor. It is important to be aware that both may require a per AP license so be sure to ask about this when exploring these options.
|Aerohive||Hive OS (Controller-less)|
|Aruba (HP)||Aruba (HP) Central|
|Extreme||Virtual Wireless Appliance|
|HP||Cloud Managed Networking|
|Cisco Meraki||Cloud Controller|
|Meru (Fortinet)||Virtual Mobility Controller|
|Zebra (Motorola)||WLAN Cloud Services|
|Ruckus (Brocade)||Virtual SmartCell Gateway (Carrier/Managed Service Provider grade)|