It's been almost a full day now and the nation of Syria remains completely cut off from the rest of the Internet (and by extension, the outside world.) Internet analysts who watched the collapse in real-time think they've figured out how it was done.
The Syrian government claims that "terrorists"—their standard euphemism for the rebels—cut the major cables supplying internet connections to the country. That's an unlikely scenario for a couple of reasons. For starters, the Internet is the rebels' most important communication tool, used to talk to each other and to spread word of the conflict around the world. There'd be no advantage for them to disable their most effective propaganda tool. (Although, the Syrian state media website is also down.)
Furthermore, there are four actual physical cables that deliver connections from the global Internet to Syria. (Image via Renesys.com) Three of them are underwater, in the Mediterranean Sea. The other comes across the Turkish border. To completely stop the Internet in the manner observed, all four would have to be severed simultaneously, an unlikely logistical challenge for the rebels, and one that still wouldn't fully explain the systematic shutdown observed by technology companies elsewhere.
Syria only has one Internet provider, which is naturally controlled by the state. All four of the cables would feed into a handful of edge routers (the starting point for an ISP network), that would then distribute all the incoming and outgoing traffic to the rest of the country. Since all the routers are controlled by one company, they could simply reconfigure the routers and then, boom. No more internet. (Network computing company CloudFlare explains it in more technical detail on their blog.)
The video below shows what it looked like on the digital end, as all of the routes from the main network to the lower level hubs were shutdown, one at a time.
This graph from Google's Transparency Report also shows in stark terms how all traffic to Google services was completely silenced, far beyond what you'd see from a mere technical glitch or power outage.
In response, Google has relaunched "Speak2Tweet," a system they set up during the Egyptian revolution last year that allows people to send tweets over the phone, without an Internet connection. However, there were also reports that phone services in Syria have been crippled as well. Plus, without the Internet, it will be nearly impossible for Syrians to find out about it.
How long this outage will continue, or why the regime felt the need to take such a drastic step (remember, they can't use the Internet now either) remains a mystery. If it's meant to be cover for some dramatic or desperate act by Bahar al-Assad, we may not want to see what has happened when the switch is turned back on.