IDG Contributor Network: The Wi-Fi network edge leads in an SDN world

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Two decades ago, the core was the place to be in campus networking. The networking battles of the 1990s concluded with the edge specialists humbled and assimilated by core product lines. Control the core, we declared, and the edge will fall into place.

But now the edge is fruitful, and the core is sterile—and for two reasons. First, the wireless interface adds mobility and complexity to the edge. Second, the new architectures of software-defined networking (SDN) and IoT are based on centralized models that take sensed information, manipulate a software representation of the network, then send control signals back to network nodes. Nodes are peers under the controller. Their importance is based on the quantity and quality of the information they can report, as well as the sophistication of the control they can apply.

Wired edge switches, on the other hand, have relatively simple functionality. Wi-Fi access requires a network edge with 802.1X authentication, dynamic VLAN assignment and mobility constructs. These are all sophisticated architectures, and they account for the emergence of specialist WLAN overlay equipment. The last decade showed traditional Ethernet switch designers were unable to build state-of-the-art Wi-Fi hardware and software into their products, although they were well-positioned in the market.

The power of the Wi-Fi network edge

However, it is the new thinking around SDN that makes the Wi-Fi network edge especially powerful. Its centralized, abstracted network model must be fed with the current state of the network. Where can it get the most information on network state?  From the edge.

Access points sense the RF signals from connected devices, identifying location and tracking mobility. They are involved in authentication, learning the identity and status of devices. They monitor ARP, DHCP, mDNS, DNS and other protocols, providing insights into connectivity requirements. And they are in the data path, able to profile and report traffic flows. No other network node is placed to monitor all these protocols. The farther one travels from the edge towards the core, the more information is lost.

Thus far, SDN implementations have dealt mostly with optimum routing through the network, treating the access point like a wired edge switch—although there have already been various research projects seeking to extend the model. But as SDN technology matures, it will place more emphasis on the wireless network edge to report complete information on client devices and traffic flows to the central controller.

And in the opposite direction, the controller will apply policy to its model of the network, its traffic and device requirements, sending control signals to reconfigure the physical network. To which network nodes will these signals be directed? Surely, to the edge. This is where authentication can be interrupted, addresses dynamically assigned, ARP and other multicast protocols passed or blocked to create connectivity maps and quality of service, and data traffic interdicted, diverted or modified for appropriate levels of user experience.

Interfaces are important in our universe. The biosphere, software APIs, human skin, (some even consider the white cliffs of Dover a significant interface)—the list is long, and we can now add another, the wireless network edge. Wireless access points have not yet received the attention they deserve in architectural discussions, but they are set to become the principal sensor and policy-enforcement points of the campus network, continuing the resurgence of the edge.

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