[spc476]

Not quite true. If you are driving (say, along I-95 on a long trip) it's true that your phone will disassociate with one tower going out of range to a new tower coming into range, and the phone switches behind the towers will transfer "ownership" (more like association), but once you (if you aren't driving, or your passenger) accept a phone call, things get a bit different.

The cell phone is answered. So, it goes from switch O (the caller) to switch A (where your cell phone is associated with). Eventually, you'll move out of range of towers for switch A, and come into range of towers for switch B. But because the phone network is circuit switched, you can't just create a circuit from O to B. No, what happens is that A forms a connection to B, so now the call is going O -> A -> B. Talk long enough, and eventually, your call may end up going O -> A -> B -> C -> D -> E -> F.

So while it's true that your call doesn't go through multiple towers, it does go through multiple switches (as long as you are talking on the cell phone, and the cell phone is moving).

[ghshephard]

Are these links RF or Land Based? Are there any examples of fast (> 1 megabit) RF Mesh Networks with greater than 5 hops in the RF Mesh and, say, around 20 active talkers at once behind the last hops of the Mesh?

I'm happy to get 100 kbits/talker in that scenario with todays FHSS technology, 500 meters/hop, 1 watt power, 200 kHz channel width and 20 MHz of spectrum in the ISM band.

Of course, the advantage of Mesh Networks is they require little in the way of infrastructure, and scale up into the millions of nodes, with 50 million active node networks practical. But high data rates are not one of the properties of such networks.

[spc476]

Well, it's RF between the cell phone and the cell tower. Between the switches, it's most likely land based circuits, but really, they could be anything.

[chronomex]

Not quite true. They don't chain like that. A tells O that B has become a better choice, so a complex dance happens where:

a new circuit is established from O to B,

O tells A to tell the handset to move over to B-owned network infrastructure,

the handset roams over to B,

O drops the circuit to A.

This is a special case of Inter-MSC Handover, and you can read the spec at https://archive.org/stream/etsi_ts_123_009_v03.03.00/ts_1230...

The relevant section is Sec. 7.3.2, "Description of the subsequent handover procedure ii): MSC-B to MSC-B'".

(They call your "O" by "A", your "A" by "B", and your "C" by "B'" (B prime). And an MSC is a Mobile Switching Center that usually handles about half a city's worth of towers.)

[spc476]

Is that while a call is in progress? That sounds like what happens when a cell phone that is not in use, transfers from switch to switch like you describe.

Or the instructor I had taught us outdated information.

[chronomex]

Handover is for established calls. I'm not surprised your instructor wasn't quite spot-on, GSM is not a simple protocol.