A funny thing happened on the way to the toilet…

Warning: Technical detail ahead! If your eyes start to glaze over, skip to the end where there are some links to videos. 🙂

I had one of those weird experiences this morning where lots of technology and mundane basic things bump up against each other. I was on the way to emptying a full potty when my mobile phone rang in my pocket. Yesterday I had the afternoon off and just as I was leaving a minor crisis blew up so I forwarded my work phone to my mobile in case anyone rang me about it. The colleague who rang me didn’t realise this, called my extension and got through to my mobile.

This was all complicated by the fact that he was phoning from India (he’s Indian) and the large American company for which we work has made the phones in India use VOIP, plus plumbed this in so that they appear as American phone numbers! While I was talking to him, I was trying to work out what route the call was taking, and this made my head spin. I think it was like this:

1. My colleague’s extension talked to his local switchboard.
2. The switchboard realised it was an external call, and so handed it over to the company VOIP network.
3. The VOIP network carried it from India to America, which involves crossing the Pacific Ocean by undersea cable or satellite.
4. In America, the VOIP network pushed it out to the local phone exchange.
5. The local US phone exchange realised it wasn’t a local call and so it went up to the nearest US trunk exchange.
6. The trunk exchange saw that it was a UK call and so sent it over to the appropriate trunk exchange to go over the Atlantic Ocean.
7. It crossed the Atlantic via undersea cables or satellite.
8. When it arrived in the UK, it travelled through the UK trunk network to the local exchange nearest to my office.
9. The local exchange sent it to my office’s switchboard.
10. My office’s switchboard put it through to my extension.
11. As call forwarding was set up on my extension it bounced back to the switchboard.
12. The switchboard dialled back out to the local exchange.
13. The local exchange realised it wasn’t a local land-line call and so sent it to the nearest trunk exchange.
14. The UK (land-line) trunk network worked out it was a call to my mobile operator’s network and so pushed the call over to that network.
15. The mobile network looked up the last base station that my phone had registered with and routed the call through to that base station.
16. Electro-magnetic waves travelled from the base station to the phone in my pocket!

It all just worked! (If, instead of being at home, I’d gone to France it would have been even more complicated, but it would still have just worked!) My colleague didn’t need to worry about anything more than my phone number – not what kind of phone he was dialling, what kind of network it was attached to or anything.

The reason why it all just works is largely due to standards for phone networks, as governed by the ITU, which is part of the UN. Because of the standards, each part of the phone network involved needn’t worry about anything further than the next step in the journey, for instance the Indian switchboard just said “VOIP network: you deal with it”.

At work we put some of our software on top of something another company sold to mobile phone operators, which meant we felt the sharp end of the ITU standards. (The mobile phone thing looked like nothing more than a large computer to our software.) Our software had to, come what may, produce an answer within so many milliseconds of CPU time otherwise the thing expecting our answer would just give up and assume the answer was “no”.

All this amazing leaping across the world is brain-boggling enough, but that’s just looking at things from the point of view of the phone network. If you dig down into lines of code running on computers, or logic gates in the chips on those computers your head starts to overheat! It’s a bit like the excellent powers of ten film from the 70s (or the more recent versions by The Simpsons or Men in Black).