[crazygringo]

> and somewhat often a bug would only manifest itself on a single cell tower.

I can easily understand different brands/products/generations having their quirks, but I'm struggling to imagine what the source of uniqueness could be for a single cell tower.

Is it a huge variety of config options, that certain combinations of settings turn out to be rare? Or is it literally just something broken like malfunctioning hardware?

[8fingerlouie]

> but I’m struggling to imagine what the source of uniqueness could be for a single cell tower.

GSM is/was a complex beast. Each base station can only handle 8 simultaneous phone calls (the old 2G/3G multiplexed ones, not modern VoIP), so in crowded areas they’re usually configured with a very short range. Some large conferences have had base stations with their range measured in single digit meters (<30 ft).

Furthermore, like WiFi, bandwidth is limited, so base stations are deployed in a “beehive like pattern”, like a triangle with a base station radiating out from each leg, and broadcasting at different frequencies to it’s neighbors.

That alone leaves a lot of room for configuration errors on each individual base stations, but when i say “a single cell tower”, i meant on that drive. The bug might be with a specific firmware version of that base station manufacturer, or that particular hardware revision, or simply a configuration error, or maybe it was a bug in our software and/or radio firmware. There are a lot of “moving parts” that needs to be investigated, but from a developer perspective, the error only occurred on one base station.

It could of course also turn out to be a “broken” base station, and often enough we would fail to find the error, and had to contact the network operator to get them to help trace down the error.

[k0k0]

> Each base station can only handle 8 simultaneous phone calls

Perhaps you are confusing that each GSM transceiver (TRX) provides 8 time-division channels with call capacity, but most cells and specifically the BTS in GSM parlance, especially any in a well populated area have/had way more than one transceiver. 30-40 was not unheard of in later equipment, though 10 or so was more typical. Late in GSM's life there was another technique to squeeze more channels, OSC.

Furthermore those 8 TDMA slots could be split in 1/2 or 1/4 with lower rate codecs, so it was more than 8 per TRX as well.

anything bigger than a picocell would carry way more than 8 simultaneous calls.

> Some large conferences have had base stations with their range measured in single digit meters (<30 ft)

Femtocells are still a thing today. Not so much to do with frequency capacity.

[8fingerlouie]

> Perhaps you are confusing that each GSM transceiver (TRX) provides 8 time-division channels with call capacity

I was talking 2G/3G. It has been 20 years since i wrote software for mobile phones :) But i should probably have been more specific and said you can have 8 active calls per channel. And i have no doubt today with 4G/5G and a shift to VoIP that you can have way more than that.

> Femtocells are still a thing today. Not so much to do with frequency capacity.

I was attempting to refer to the scalability/complexity of the network, which scales from 10s of kilometers to 10s of meters, or even more/less.

But as i said, i wrote software for the phones. My understanding of the network side of things was/is limited to the rudimentary knowledge needed to write that, and i'm happy to be corrected.

[giantrobot]

Cellular base stations have lots of configurables. There's a lot of timing related settings in cellular radios. So you've got a thousand places to introduce a 500 Mile Email problem[0]. Some timing settings can run up against timing consts in the client firmware.

For instance towers around an airport might have some bands running with reduced power or disabled. This reduces cell size/overlap on those towers requiring more frequent handoffs between those towers. A client firmware might have a bug or unrealistic const set that fails in that frequent handoff situation. So it's a bug that only happens on some 5G bands near an airport but only during the summer because the more arid conditions increase microwave propagation by 1dB.

[0] https://web.mit.edu/jemorris/humor/500-miles