Author Topic: Cell Call Routing - International  (Read 532 times)

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Offline rstofer

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Cell Call Routing - International
« on: August 02, 2018, 08:09:58 pm »
A friend lives down the street and we both subscribe to the same cell service.  I pretty much understand how this call is routed.

I even think I understand how this works across multiple carriers but maybe I don't...

Now, let's say my friend gets on an airplane and travels 16 time zones away (or 8 the other way...).  How does the cell phone network know how to route my next call to some foreign country?  Clearly, it works.  What I am really wanting to find out is how the routing actually works.  How does the network know where to look?  Is there a single master list of the location of every cell phone in the world?  Why wouldn't the provider simply say "not available" and dump the call?  Not only does the router have to send the call to the right country (which might have changed a couple of minutes ago as they walked across a border) but to the right cell tower.

Any links to technical answers?  I searched Google and all I got was trash, mostly related to costs and services.

Thanks!
 

Online PA0PBZ

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Re: Cell Call Routing - International
« Reply #1 on: August 02, 2018, 08:18:23 pm »
Your friends cellphone logs into the foreign network, and then I guess this foreign network tells the home network where the phone is - at least that is what I would do when I had to design it  ;)
Keyboard error: Press F1 to continue.
 

Offline Halcyon

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Re: Cell Call Routing - International
« Reply #2 on: August 02, 2018, 08:39:38 pm »
Some of these links might help you in understanding how mobile calls are routed:

https://en.wikipedia.org/wiki/Network_switching_subsystem

https://en.wikipedia.org/wiki/Mobility_management
 

Offline rstofer

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Re: Cell Call Routing - International
« Reply #3 on: August 02, 2018, 09:16:10 pm »
Yes, those documents cover it nicely.

There really is a master list!  It's distributed somewhat but basically that's how it's done.  The HLR (Home Location Register) tells the subsciber's home office where the client is located.  Apparently this happens at every cell tower handoff - worldwide!
 

Offline helius

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Re: Cell Call Routing - International
« Reply #4 on: August 02, 2018, 09:21:43 pm »
You know how your phone has an option to enable or disable "roaming"? What is roaming?
It's the ability of the phone to log in to a network other than its home network. Usually this involves a different tariff schedule that can result in increased charges (if you have a post-paid account). The current location of a mobile station (phone) is being tracked all the time by the cell towers for two reasons: first, so that incoming calls can be routed to the correct cell tower/base station to reach the phone, and second, so that handoff between towers can be managed without interrupting ongoing calls.

The cell handoff in the midst of a call, without interruption, may not work smoothly or at all when roaming between different networks. It only has to work when you stay within the same network and move between cell towers.
 


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