Plexxi distinguishes itself from other controller-based SDN architectures in a couple of key ways. First, its ToR switch includes an optical interconnect. The company claims that its optical interconnect provides up to 400 Gbps of capacity per switch. Up to 250 Plexxi switches can be linked together via optical ports built into each switch. "We employ WDM technologies that allow for optical meshes of connectivity," says CEO and co-founder David Husak.
Second, Plexxi doesn't use OpenFlow to communicate between its controller and its switches. This sets Plexxi apart from a large number of established vendors, including HP, IBM, NEC and, to some extent, Cisco that promote an architecture that relies on a controller-plus-OpenFlow design.
Instead, the company uses a two-tier controller architecture, in which some controller functions reside on each individual switch (a co-controller, in Plexxi's parlance). The output from the central controller consists of what Plexxi calls a set of network directives. "The co-controller on each switch is responsible for translating those network directives into device-specific information like flow table entries," said Plexxi co-founder Mat Mathews in an e-mail.
Mathews said the central controller can communicate a partially specified topology to the Plexxi switches, in which it provides several path options for a given destination. The switches then figure out how to distribute traffic using those paths. The controller can also define a specific end-to-end path for a given workload.
Rather than transform switches into dumb-but-fast devices that simply shuttle traffic back and forth at the whim of the controller, Husak said, there's value in ensuring that individual switches retain some network intelligence. "There's a lot of elements and features of the layered protocol stack that have self-healing and the ability to do rapid device detection and bring up and down connections, and we wanted to preserve those functions," he said.
Plexxi's API exposes the controller to third-party systems, which can communicate network requirements to the controller. "Initially, they can pull information out of VMware's VCenter or VCloud Director and use that information to make decisions on how they build a network," says Eric Hanselman, research director for networks at 451 Research.
Many Paths to SDN
Plexxi isn't the only startup tackling the SDN market, nor is it the only startup to forgo OpenFlow. This October, a startup called Midokura announced a beta version of its MidoNet software. MidoNet is designed to run on Linux servers at the edge of network. The software sets up tunnels that can run over an IP network, creating a virtual network overlay that moves traffic through physical devices. Back in the OpenFlow camp, a startup called Big Switch Networks launched a software controller and a pair of SDN applications.
451 Research's Hanselman says Plexxi should appeal to organizations with workloads that can take advantage of the optical interconnect, such as financial services companies engaged in high-frequency trading or media companies that need to move large files.
"If you want to slice and dice a bunch of 1Gig and 10Gig links, OpenFlow does that handily, and you can do it with low-cost systems," he says. "If you want high capacity and flexibility, that's where Plexxi holds an advantage."
That capacity comes at a price: Plexxi's switches start at $64,000, and the software controller is licensed at $5,000 per switch. The company says its Switch-1 offers 32 10-Gbps and 4 40-Gbps ports on each box in addition to the optical port.