In keeping with a WLAN industry trend manufacturer is pushing controller-based intelligence to access points on the edge.rnrn
During a three-year engineering push, Motorola engineers rewrote the systems software for the company’s WiNG (Wireless Next Generation) -branded controllers and access points, including the network stack. Part of the effort, in keeping with a WLAN industry trend, was to push controller-based intelligence out to the access points on the edge.
Two vendors, Aerohive Networks Inc. and Meraki Inc., have taken more radical steps. The former is shifting all control functions into its access points, with a separate management application; the latter is shifting them to a cloud-based service, with Web access. Aerohive recently upgraded its network OS, and Meraki added management tools to its cloud controller.
The software is being phased into Motorola’s existing WLAN products, starting now with the RFS 4000 controller and AP 650 access point. The software will be ready for the RFS 6000 and 7000 controllers and the AP 6511, 7131 and 7181 models during first quarter of 2011.
One result of the new Motorola architecture, dubbed WiNG 5, is to move local data routing decisions to the access point from the controller. The access point can route traffic to other clients (and in some implementations, even to other access points), reducing the load on the network and the controller. This can boost streaming video and VoIP performance and quality by eliminating the round trip to the controller, especially when that trip has to take place over a WAN connection.
Another result is a flexible approach to a wide range of control tasks – such as roaming, authentication, encryption and the like – that often can be handled locally by the access point, easing the processing burden on the controller.
In a live demonstration by Motorola, 80 laptop PCs simultaneously displayed flawless unicast video streamed from a server, through an Ethernet switch, to a single Motorola AP 7131, with a Motorola controller also connected to the switch.
There were two other demonstrations showing the power of the new architecture. In one, the access point detected a radio interference source that froze an attached laptop. The AP quickly relocated the laptop to a clear channel. In another, the access point’s L2/L3 stateful firewall quickly detected an unauthorized client streaming video and blocked it, causing it to freeze on another laptop’s display, while leaving unaffected an authorized video stream to the same laptop.
“I found the demonstrations fairly impressive,” says Craig Mathias, principal of Farpoint Group, a wireless consulting firm in Ashland, Mass. He cautions that there are as yet no mathematical models, or even direct performance comparisons, that can help users or even researchers assess different WLAN architectures. And the more traditional centralized controller approach of Cisco and Aruba has not kept them from being, respectively, number 1 and number 2 in WLAN market share for the enterprise.
But Mathias expects that over time, data functions will become more distributed in WLANs, while management remains centralized. Motorola, he says, is able to be agnostic about where control functions should be located: some work best at the access point, others at the controller.
One Motorola Wi-Fi customer planning to upgrade to the new software is Keller Independent School District, Keller, Texas, in the Dallas-Fort Worth area. Currently it deploys more than 1,000 access points to blanket 38 campuses with a Wi-Fi network supporting 33,000 students and 2,400 teachers.
“In the short term it will give us [Wi-Fi] sustainability,” says Joe Griffith, Keller’s chief technology officer. “If a WAN connection goes out or a controller fails, [the new architecture] lets the access points remain in operation.”
Another advantage, Griffith says, is the ability to handle an expected steep rise in Wi-Fi usage and traffic. “By routing traffic at the edge, it increases capacity of the overall network,” he says.
Motorola makes some dramatic claims about such scaling. The WiNGs architecture lets each existing controller support eight times as many access points as previously, says Amit Sinha, CTO for Motorola WLAN. The RFS 7000, for example, used to have a maximum access point load of 256; now, it’s just over 1,000. “With distributed packet forwarding [by a local WiNGs access point], you and I can have a local Apple iOS FaceTime without putting that load on the controller,” he says.
In a branch office, one of the WiNG 5 access points can become a “virtual controller” to the others, coordinating a variety of functions if the WAN link to the remote controller is down, according to Sinha.
As part of the software rewrite, Motorola also analyzed the performance of the network stack, which traditionally in wireless LANs remains optimized for long-packet frames as in the wired LAN, according to Sinha. But a Motorola traffic analysis found much wireless traffic, especially for voice, uses short packets. Motorola retooled the stack to reflect that, making it 10 times more efficient in handling short packets, says Sinha.
Sinha defended his characterization of controllers as potential “chokepoints,” especially with 11n access points handling 100-160 Mbps throughput, and especially where there is only a comparatively low bandwidth WAN connection from branch office access points to a data center-based WLAN controller. “Beefing up the CPU and the memory on the controller doesn’t help you in those cases,” he says.
Symbol Technology was the first to introduce a “wireless switch,” the precursor of the controller, a model widely adopted and deployed in the past decade. The controller processes all WLAN traffic from dependent or “thin” access points. Classically, the controller handled everything: encrypting and routing traffic, authorization and security, roaming. Over the past few years, WLAN vendors have been pushing a range of these functions back down to the access points, notably making them local routers that only pass back to the controller traffic that needs to be routed to clients attached to other access points.