Iran has 6 major telecommunications companies, but all internet traffic is filtered through the state owned Data communication Company of Iran (or DCI), which is essentially the firewall for network traffic in and out of Iran. Arbor Networks, an IT security research firm, has a network monitoring tool called ATLAS 2.0 which monitors about 80% of the global internet traffic. The last entry on Arbor researcher Craig Labovitz's blog lays out the cyber battlefield.
In normal times, DCI carries roughly 5 Gbps of traffic (with a reported capacity of 12 Gbps) through 6 upstream regional and global Internet providers. For the region, this represents an average level of Internet infrastructure (for purposes of perspective, a mid size ISP in Michigan carries roughly the same level of traffic).
One the day after the elections on June 13th at 1:30pm GMT (9:30am EDT and 6:00pm Tehran / IRDT), Iran dropped off the Internet. All six regional and global providers connecting Iran to the rest of the world saw a near complete loss of traffic.
Most Internet traffic to Iran goes through Reliance (formerly Flag) Telecom, the major Asia Pacific region underseas cable operator. Singtel, a major pan-Asian provider and Türk Telekom also provide significant transit. Initially, DCI severed most of the major transit connections into Iran. Within a few hours, a trickle of traffic returned across TeliaSonera, Reliance and SignTel — all well under 1 Gbps. As of 6:30am GMT June 16, traffic levels returned to roughly 70% of normal with Reliance traffic climbing by more than a Gigabit.
Many people are speculating why Iran is running at around 70% of normal. Most security researchers agree it is because Iran is conducting packet inspection, but the methods Iran is using to conduct packet inspection is purely speculative. The main point is, 5 Gbps is not much, and on the cyber battlefield Iran is not only limited due to bandwidth, but bandwidth control is limited due to probable ownership of Chinese IT hardware usually 2-3 generations behind western equivalents (often clones of western hardware 2-3 generations older than modern versions). Because Iran cannot conduct global business with partners without the internet, shutting down the internet brings economic problems that would only compound the political problems taking place in the Iranian streets.
For years strategic thinkers have suggested that the technological connectivity requirements for global commerce is a dynamic that will radically influence the calculations of governments that lack transparency. We are seeing that dynamic at work in how the Iranian government is currently managing this crisis of information control in and out of Iran.