My old phone: Why AT&T sent me a free phone, and what circuit-switched means | Hacker News Reader

My old phone: Why AT&T sent me a free phone, and what circuit-switched means

robotsinplainenglish.com

2 pointsripe4 comments

For over a year now, I've been writing short articles for non-technical people to read. Usually I try to use something in the news as an opportunity to teach some simple concept.

This is my latest article. I use the fact that AT&T is mailing me a free phone, to explain the difference between circuit-switching and packet-switching.

This article is terribly inaccurate.

3G networks are packet switched just like 4g.

4G is VOIP, witch just means those packets are routed over IP (internet protocol).

Circuit switching pretty much only exists as the last mile on aging landlines.

EDIT: Also, circuit switched cell phones are a physical impossibility. A circuit switched phone has to be hard wired to a network, otherwise there is no circuit.

You're right. I'm trying to distinguish VoLTE as opposed to voice calls on 3G. That's the piece that's missing in the old phone. How would you get at that distinction? Any alternative way to explain that would be useful.

You should start with some internet history. The internet was born out of the a military desire to have robust network that could function if nodes or data links went down.

In the case of the circuit switched network, imagine all the coper wires connecting New York to San Fransisco were cut. It might be possible to for residents of both cities to make calls to Chicago and Denver, but New York to San Fransisco would be impossible until the copper lines were repaired.

The packet switch network that replaced the old circuit switched network used fixed manually configured routes, so the same thing could happen if the digital links connectyng New York and Sanfransico failed.

On a IP protocol network, any two connected devices should be able to communicate. Severying the links between New York and San Fransisco wouldn't cause an outage, because packates could go through Chicago.

3G Phones maintained parralel networks for voice and data. An IP network for data, and a separate (probably) non IP network for calls.

VolTE allows carriers to do away with the second network and send all voice over the data network. It is kind of like a skype app built into the dialer.

This is a bit of an oversimplification, it is possible your 3g calls were being bridged over an ip network. I hope this gives you a better understanding.

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