To avoid the congestion of the public internet, scientists, the military and the managers of huge “cloud computing” data centers have created private information superhighways – dedicated fiber-optic systems known as lambda networks. As it turns out, these private internet highways are riddled with potholes.
To look into the glitch causes – and their possible cures – in what were supposed to be perfect systems, Hakim Weatherspoon, Cornell assistant professor of computer science, has received a National Science Foundation (NSF) Early Career Award, designed to support young researchers exploring cutting-edge ideas, of about $600,000, and more than $750,000 from the Defense Advanced Projects Research Administration (DARPA) Computer Science Study Panel. DARPA also will provide access to military computer facilities for testing.
Using extremely precise sending and receiving devices, Weatherspoon and colleagues have found that the pulses of laser light representing the ones and zeros of computer communication may start out evenly spaced, but sometimes arrive at their destination in a bumper-to-bumper “convoy,” hitting the receiving computer faster than it can process them. (Think of Lucille Ball trying to keep up with the candy factory assembly line.) Data can be corrupted, and data packets that are dropped have to be resent, slowing the system down.
Weatherspoon uses Cornell’s membership in the National Lambda Rail high-speed fiber-optic research network to create “Cornell NLR Rings,” dedicated loops that start in Ithaca and carry data packets to New York, Chicago, Denver or, in the largest loop, through Seattle and Los Angeles and finally back home.
Weathersoon, physics postdoctoral researcher Daniel Freedman and graduate student Tudor Marian developed an apparatus that uses a precisely modulated laser to generate packets of optical signals to send around these loops, then analyze what comes back with sub-picosecond accuracy. The original instrument, known as the Software Defined Network Adapter, was an assembly of lasers and oscilloscopes from a physics lab, taking up significant floor space. The NSF funding will support development of the next generation, the Software-defined Network Interface Card (SoNIC), a standard accessory card that plugs into any computer. SoNIC cards will be available to other researchers, Weatherspoon said.
Measurements with the original device showed that data glitches increase with the number of “hops” a signal takes. Weatherspoon believes this shows that the problem lies in the routers the signals must pass through on their travels. Routers read the addresses incorporated in incoming optical data packets and resend them on the best route to their destination. Some routers may let packets pile up and then send them out in bursts, like a row of cars that have pulled up at a traffic light and then started off all together, Weatherspoon suggests. The exact cause of this phenomenon is not yet known, he said, but the effect is clear.
The direct computer interface of the SoNIC device will allow the researchers to observe network behavior in real time and run software that tweaks the signals they send on the fly. They are not limited to the standard protocols of the Internet, but can create data packets in any form they choose, to develop and test new formats that will avoid or correct for the glitches introduced in transit.
