In the U.S., about 20% of calls to cellphones and 40% to landlines are robocalls — many of them scams. Tuesday is the deadline for voice service providers, including some phone companies, to show the Federal Communications Commission what steps they’re taking to stop robocalls. Marketplace’s Marielle Segarra speaks with Brad Reaves, a professor of computer science at North Carolina State University. Reaves said the FCC is telling these companies to be on the lookout for clear signs of fraud.