Is All Enterprise Wi-Fi Equal?
This series of posts is dedicated to helping network managers plan a WLAN deployment by answering questions commonly asked when shopping for a long-term Wi-Fi solution.
As WLAN standards evolve to support faster data rates, so to does the underpinning infrastructure. Back in the late 90’s when Wi-Fi was in its infancy, access points operated independently of each other. They would share common settings such as SSID, but fast roaming, load balancing, RF coordination, etc were non-existent.
In the 2000’s when Wi-Fi became mainstream, a control plane was required if Wi-Fi were to survive as an enterprise technology. With chipset prices at a premium, the WLAN controller was created to centralize the control plane and provide a smarter, coordinated solution.
Curious about the history of cloud Wi-Fi? Read Controllers Are Dead (And Why)
Although WLAN controllers are still widely used today, there is a stronger emphasis on cloud-enabled solutions, and de-centralizing the control plane to the edge of the network. Let’s us look at the various options available today.
1) Control Plane Summary
The control plane is the set of real-time operations within the infrastructure, such as controlling connections, disseminating connectivity information, and calculating optimal path. In Wi-Fi this can include RF management, roaming, load balancing, mesh, policy enforcement and many more critical operations.
A shared control plane in any infrastructure system can be achieved in either of two ways: centralized or distributed.
In both switching and routing, the control plane is distributed, operated by protocols (e.g. spanning tree, OSPF) between intelligent devices. In the past, the control plane in Wi-Fi technologies was centralized, but this has changed in the last couple of years with all of the major WLAN vendors moving towards a distributed control plane model.
2) Architecture Advancements
“WLAN controllers were purely an economic decision at the time. To place greater processing power into the access points themselves was simply cost prohibitive” – Bob O’Hara, inventor of the WLAN Controller.
At the time of their creation, controllers eased the management and security headaches that non-pervasive networks comprised of autonomous access points would cause. Today, however, with the increased reliance on Wi-Fi, expanding networks and increased performance requirements, the centralized model has severe architectural limitations, including data bottlenecks, scalability, reliance, and unnecessary cost.
Recognizing some of the shortfalls of the fully centralized controller model, vendors began to adapt their solutions through virtualization and portfolio integration. Virtualization provided increased scalalbility as the host’s proccessor, memory, and network interfaces could be increased as required.
This model also placed some of the intelligence back into the access points, along with the introduction of local data forwarding. Alternative offerings included the embedding of the controller within access layer switches, firewalls and other networking solutions, which helped to reduce solution components. For smaller deployments, an access point within a cluster could also act as a controller for a group of local access points.
While these hybrid models offer increased deployment flexibility, there are some tradeoffs to be aware of.
The reality is that most vendors were attempting to retrofit their controller architecture to deal with a more modern day network. With the controller still acting as the brain of the network, if local data forwarding was enabled, organizations would be sacrificing the usage of some important features, such as QoS and firewall policies, as they required user traffic to pass through the controller.
Solutions that integrated controller functionality into the access points would also struggle over a certain number of connected access points, given a single access point has nowhere near the processing power of a dedicated appliance (physical or virtual).
Hybrid solutions are still used by many vendors today as they are bound to their legacy architecture, having invested so heavily in the technology, however most are slowly moving away.
3) Cloud Controllers
In recent years, the cloud has proven popular with organizations looking to centralize software services and reduce costs. With access points having less reliance on controllers for features and functions, some WLAN vendors provide hosted controller services as an annual payment plan, giving organizations more flexibility with their budgeting.
Commercially this model works for many. However, technically there are still limitations. Ultimately the solution still utilizes a controller, and the access points still depend on the controller for certain functions, therefore if connectivity is lost between the two, then organizations will face an impacted service, from user connectivity to security policies and enforcement.
Additionally, although organizations purchase their hardware outright, if they forget to renew their controller license or support, then their wireless network will cease to operate, which is a major pain point for many organizations.
When evaluating solutions of this kind, it is imperative that organizations ascertain from the vendors what exactly will happen if- 1. access points lose connectivity to the cloud and 2. what happens if the controller license expires.
4) Distributed Control with Cloud Management
Leveraging the increased processing power of todays chipsets, combined with a control plane protocol (similar to OSPF and STP used in switching and routing), it has now become possible to create a fully distributed control plane, thus eliminating the need for a dedicated wireless LAN controller entirely, whether physical, virtual, or cloud-based, while maintaining a centralized management plane.
Fully distributing the control plane achieves three main benefits:
• Cost Savings – By removing controller hardware, software, and licensing, dramatic cost savings can be realized without losing functionality.
• Operational Simplicity – Using a distributed control plane is inherently resilient and allows the WLAN devices to self-organize and integrate directly into the access architecture, enforcing security policy before WLAN traffic ever traverses the wired LAN.
• Scalability and Flexibility – With every access point or networking device participating in the processing of data, much like a grid computer, the network can provide full functionality to any deployment regardless of size. Every device added to the network increases not only the coverage, but also the total compute capacity of the network.
Fully distributed control and data planes are essential for a mobile-first network, however the management plane plays a key role in the deployment and support of the wireless LAN and should remain centralized.
All posts in this WLAN Buyer’s Guide series:
Part 5) Is All Enterprise Wi-Fi Equal?