Over-the-Air: Virtualized

The virtualized architecture builds upon the layering architecture, but introduces the notion of complete wireless network virtualization. Wireless LAN (WLAN) virtualization involves creating a unique virtual wireless network (a BSSID) for every mobile device. This allows the network to be partitioned for each client, providing each client with its own set of 802.11 autonegotiated features and parameters.

It's important to note that the per-device containment provided by virtualization differs from the per-device rules and access control enforcement provided by the other architectures. Containment addresses the over-the-air behavior of the client directly, using the standard to enforce the segmentation and the tight resource bounds. The client's cooperation is not needed or expected. Access control, on the other hand, is fundamentally a cooperative scheme, and clients can choose not to participate in the optional protocols required to make bidirectional access control work. Even downstream policy enforcement cannot stop a client from transmitting what it wants to upstream.

However, virtualized Wi-Fi partitions are able to maintain the per-device containment, by transferring control of the network resources from the client to the network, and then using Wi-Fi mechanisms from the network side to ensure that client behavior is limited to the resources that the client is allocated.

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Architectures and 802.11 Functions

In 802.11, the concept of an "access point" is defined to carry one BSSID and one SSID over the air to a set of clients. The access point definition includes every function necessary to make the access point a bridge to wireline Ethernet, including encryption, decryption, connection management, medium access control, and timing functions.

However, this concept is only a concept, and the architectures in the market today differ by how they divide the functions of the 802.11 access point across the actual equipment deployed in the network. In general, every architecture ensures that multiple 802.11 access point concepts can be created and operated in each physical access point, thus allowing for multiple BSSIDs—and more importantly, multiple SSIDs—per access point. This starts by having multiple radios within an access point, but is most useful by allowing multiple SSIDs per radio.

This is the point of departure for the architectures. Controller-based architectures move parts of the 802.11 access point out of each physical access point and operates them, instead, in the controller, thus sharing those parts across all of the access points. This does not violate the standard, however, because the standard was designed to allow for all kinds of mappings of logical 802.11 entities to physical devices.

Ultimately, the best way to choose which 802.11 functions should be centralized—and thus, which type of architecture to invest in when creating a voice mobility network—is to choose based on how well the features meet your needs, and not on architectural principles alone.