In France, throttling appeared to be less common. Positive tests didn’t exceed 21 percent among France Télécom’s Orange service, Neuf Cegetel, Numericable and Proxad. In Germany, it was even rarer, at levels of less than 16 percent for almost every operator including Deutsche Telekom. (I tested Glasnost on my Deutsche Telekom network in Berlin and it showed no throttling.) The one exception: Kabel Deutschland, the biggest’s domestic cable TV operator, showed throttling detected in 44 percent of 393 tests.

In Japan, NTT Docomo employed throttling in 49 percent of 471 tests, according to Glasnost. GigaInfra Broadband and Vectant had positive tests in 30 percent and 38 percent of tests, respectively. In Canada, where the population is much more spread out, and networks must cover vast territory, throttling appeared more common. It was measured in 85 percent of tests on Rogers Communications’ network and 64 percent of tests on Bell Canada.

In other parts of the world, frequent throttling was detected in smaller operators, which often have less money to build high-capacity networks. Those included: the Dubai-based Emirates Integrated Telecommunications, operator of the Du network, with 90 percent; Toya, a cable operator in Lodz, Poland, with 88 percent; TeleCentro of Argentina, with 87 percent; RLE Elisa in Estonia, with 85 percent; ASN AtHome, a Hong Kong-based cable TV operator, with 83 percent; TM Net of Malaysia, with 78 percent; Magix of Singapore, 63 percent; Cabo TVM of Portugal, 62 percent; and Bezeq of Israel, 59 percent.

Former monopolies like Telefónica of Spain, Telecom Italia, KPN of Netherlands, Telstra of Australia, Telia of Sweden, Belgacom of Belgium and Eircom of Ireland, which all still operate the largest landline networks in their countries, generally used throttling less frequently — perhaps because they didn’t have to, on their extensive networks.

Their rates of detected throttling, respectively, according to Glasnost, were: 19 percent for Telefónica and Telecom Italia, 18 percent for KPN, 34 percent for Telstra, 14 percent for Telia, 13 percent for Belgacom and 15 percent for Eircom.

In general, the Glasnost results suggest that telecom and cable TV operators, when they do use throttling, do so mostly to suppress bandwidth hogs and ensure a reasonable experience for all of their customers. Mr. Dischinger, now a computer engineer in Innsbruck, Austria, said throttling was much more commonly used by operators of mobile phone networks, which have much less capacity than landline grids.

But with operators starting to sell superfast landline broadband service for heavy data users, such as Deutsche Telekom’s high-speed fiber-to-the-home service, the competition for bandwidth — and the need for throttling — will only increase, Mr. Dischinger said.

“I highly doubt it can go on forever,” Mr. Dischinger said. “I cannot envision with the current network infrastructure they have that operators can continue to support people in the long term without more investment.”