Any message transmitted from one phone to another -- whether it's a cute video of your kid or a scandalous nude photo -- appears almost instantly on the recipient's screen. Amazing! Now, how did it actually get there?
It turns out the exact path travelled by millions of messages is long, complex, fascinating and top secret. But we got a chance to take a peek at how it works.
For this tour, kindly hosted by our friends at Verizon, we elected to send a video via Multimedia Messaging Service (MMS), simply because it's the most direct route from one phone to another. If you were to send your video via email, it would mostly travel along the same path, but there would be a couple of internet servers in the middle (Gmail to Hotmail, for instance).
MMS messages today travel over a carrier's fastest available network, which usually means 3G or 4G. This is different from how Short Messaging Service (SMS) text messages travel -- those transmissions essentially hitch a ride on the small-bandwidth communication channel your handset uses to check in with local towers.
The large Mobile Switching Center (MSC) you see in the video is one of over 200 regional hubs Verizon has in the US. These are hubs for the thousands of cell sites and towers. The radio transmissions essentially operate by line of sight. In flat, rural areas a single tower may cover a 8km radius. But in big cities, where there is far more interference, the antennas are generally mounted to the tops of tall buildings, and there may be one as frequently as every few blocks.
The cell sites are powered in the same basic way as the larger Mobile Switching Center. They run off a rack of large, commercial batteries which are constantly being charged by the municipal grid. Should the grid fail, there shouldn't be any interruption. The sites have a room with emergency generators to keep those batteries charging and everything running smoothly. It's really comforting to see those kinds of fail-safes in place. In the event of a disaster, you know you could still browse LOLCats reach your loved ones.
So, the broad-stroke summary goes like this: data goes from your phone to a 3G/4G antenna on top of a cell site. The cell site processes the data, then sends it over telecomm fibre optic cable to the Mobile Switching Center. The MSC does a lot of highly technical stuff with that data, then sends it (again via fibre optic) to the carrier's IMS Core. That's where the majority of the data processing happens and where the right app to handle the data is selected. The data then follows that path in reverse -- MSC to cell site, then to the antenna, and finally to the receiving phone.
When you send any MMS file, the data follows this same process, even if you and your friend are sitting in the same room. Think about how many steps there are, how physically far the data travels, and yet how quickly that data gets from one device to another. It really is remarkable.
Big thanks to Tom Pica, Yatin Patel, Albert Aydin and Brenda Raney at Verizon for making this happen.