Microsoft builds low-cost datacentre switch

The low-cost ServerSwitch hardware marries modifiable server and control software with a programmable Asic, which Microsoft says can be used to test datacentre networks

Microsoft researchers have developed a low-cost switch, designed to be easily reprogrammable for testing a range of datacentre networks.

The $400 (£250) ServerSwitch card is programmable via general APIs that are not dependent on a specific switching processor, and it can be plugged into most industry-standard servers, the researchers said in a white paper published on Wednesday.

It differs from most switches in that it splits switch functions between a standard dedicated Asic switching chip and a multicore commodity server CPU. Typically, switches process data packets using a switching chip only.

"ServerSwitch explores the design space of combining a high-performance Asic switching chip [that has] limited programmability with a fully programmable multicore commodity server," the Microsoft team said.

Packet handling

The server CPU sets the policies for how packets are handled and routed. To allow the CPU to work in tandem with the switching chip, in-switch bandwidth is boosted and latency reduced via additional Network Interface Controllers (NICs). Data is passed between the card and the server via Peripheral Component Interconnect Express (PCIe) protocols.

"ServerSwitch uses a commodity switching chip for various customised packet forwarding and leverages the server CPU for control and data-plane packet processing," the team said.

In the paper, Microsoft described using ServerSwitch with a gigabit Broadcom switching chip, but said any switching chip would work.

Switching motivations

Microsoft has developed a common set of APIs for programming the ServerSwitch, so that developers can program and control the card without having to take the hardware used into consideration. The switch can be programmed via the major C or C++ languages.

"ServerSwitch is motivated by the observation that commodity Ethernet switching chips are becoming programmable and that the PCIe interface provides high throughput and low latency between the server CPU and I/O subsystem," the researchers wrote.

The switch has been inspired by and could possibly augment the OpenFlow specification, the Microsoft team said. OpenFlow functions in a similar way to ServerSwitch and passes information between the card and the server via a protocol. Both technologies "aim towards a more programmable networking platform", Microsoft noted in the white paper.

However, Microsoft believes that OpenFlow project's decision to centralise its protocol around a separate hardware controller means that ServerSwitch could prove the stronger contender. Unlike OpenFlow, ServerSwitch places the overall packet control closer to the switching hardware.

Microsoft hopes the ServerSwitch will be used in network research and is going to release the full specifications of the ServerSwitch card and software package to the networking research community "in the future".

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