Dimming the Internet: Detecting Throttling as a Mechanism of Censorship in Iran

Today, the Center for Global Communication Studies at the Annenberg School for Communication releases “Dimming the Internet: Detecting Throttling as a Mechanism of Censorship in Iran,” a documentation on three years of the use of bandwidth throttling as a means of political censorship in Iran, on the public scientific publishing site arXiv.

Read the full report here.

In the days immediately following the contested June 2009 Presidential election, Iranians attempting to reach news content and social media platforms were subject to unprecedented levels of the degradation, blocking and jamming of communications channels. Rather than shut down networks, which would draw attention and controversy, the government was rumored to have slowed connection speeds to rates that would render the Internet nearly unusable, especially for the consumption and distribution of multimedia content. Ever since, the history of the Internet in Iran is defined by sensational headlines such as “Iran Disrupts Internet Service Ahead of Protests” and “Internet in ‘coma’ as Iran election looms,” drawing a direct line between the usability of online media and the political stability of the country. Iran is not alone in this behavior, with Syria, Bahrain, Myanmar and Tibet utilizing similar tactics. However, media coverage often paints it as the most aggressive. For governments threatened by public expression, the throttling of Internet connectivity appears to be an increasingly preferred and stealthy method of stifling the free flow of information.

In the paper “Dimming the Internet: Detecting Throttling as a Mechanism of Censorship in Iran,” released today on the open publication repository arXiv, Iran Media Program affiliated researcher Collin Anderson used a three-year dataset of network measurements as a monitoring service for political throttling, then applied the methodology to shed light on the recent history of censorship in Iran, and finds that Iran’s Internet has experienced prolonged and significant disruptions timed annually near the anniversary of the Islamic Revolution and 25 Bahman, the first anniversary of the contested elections, and protests over the depreciation of the value of the Iranian Rial. This suspected interference often directly matched more overt forms of censorship, including international satellite jamming. Through the Measurement Lab (M-Lab) platform, anti-censorship researchers gain a diverse and non-partisan perspective on a network that is often opaque and difficult to access from outside. The results described not only shed light on instances of censorship, but also the manner in which public networks are subjected to a greater degree of disruption than those of business, universities and governments.


The methodology developed for “Dimming the Internet” is not only useful for investigating past trends in access, but also actively monitoring future disruption. Last week, as Iran approached its first Presidential election since the Green Movement, the domestic security apparatus made clear that foreign and independent media would not be allowed to interfere with the orderly election plans made by the state. Persian and English-language social media describes the slow ramp up of the Filternet, beginning in early February with the blocking of Internet telephony and VPN services.

The Iran Media Program actively monitored as the international Internet connectivity of Iranians was subjected to artificial throttling, beginning in extremity three weeks before the election.


After the election, Iran’s Internet speed returns to ‘normal’, using methodology from ‘Dimming the Internet.’

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In both “Dimming the Internet” and its recent election monitoring, researchers were able to use M-Lab to narrow the possibility that such instances were the result of common network failures, such as cut cables. Iran is able to accomplish such interference through the physical centralization of international communications gateways and domestic network linkages around a state-controlled entity, the Telecommunication Company of Iran (TCI). This arrangement facilitates anti-competitive and potentially undemocratic practices that would be more administratively difficult and economically expensive in an open and multi-stakeholder telecommunications market. This design is not specific to Iran alone nor is it an indicator of a government’s desire to control citizen access. However, when the network monitoring company Renesys addressed this topic in response to the Internet shutdowns of Egypt and Syria, they framed the dangers and fragility of this centralization of as “the number of phone calls (or legal writs, or infrastructure attacks) that would have to be performed in order to decouple the domestic Internet from the global Internet,” naming 61 countries at ‘severe risk’ for disconnection.


As stories of connection throttling timed with political instability grow and access to international communications platforms remains a necessary means for expression otherwise denied, “Dimming the Internet” provides a framework for accountability on a trend that thus far has been opaque. In the coming months, the Center for Global Communication Research at the Annenberg School for Communication will expand on this methodology as a means to account for historical cases and monitor this phenomenon on an ongoing basis globally.

“Dimming the Internet” is supported by the Center for Global Communication Studies at the University of Pennsylvania’s Annenberg School for Communication and Google Research.

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