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Comment by Spivak | Hacker News Reader

I'm surprised the major cell providers are cool with letting randos operate cell towers that back into an unknown untrusted ISP and their customers will automatically switch to when in range. It's unbelievably chill for companies that are usually so concerned about their image and controlling the whole experience end to end.

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>I'm surprised the major cell providers are cool with letting randos operate cell towers that back into an unknown untrusted ISP and their customers will automatically switch to when in range.

A lot of office buildings have these in them. I think the personal ones are how they get around some of the issues with government requiring them to build networks to certain coverage. They just don't build it out and when someone complains they offer them one of these.

Also because a lot of office and residential towers have people high above street level, and the buildings have radiation-minimizing windows so that no cell signal can penetrate. The cell companies put their sites 30 feet above the street, not 600+ feet up.

Femtocells are remotely controlled by the carrier, they require GPS location (and maybe spectrum sensing), and I assume the backhaul is over VPN. Obviously they can't guarantee any QoS but it's better than having no signal.

(Fun trivia: Our office paid $XX,000 for AT&T MicroCells which wouldn't activate because they couldn't get GPS signal.)

Eh, assuming it's 4G LTE (or above), it's literally the same thing as Wi-Fi calling. This is technically called IMS (IP Multimedia Subsystem, https://en.wikipedia.org/wiki/IP_Multimedia_Subsystem), and is powered by "magic" DNS (no kidding, everything points to 3gppnetwork.org) and literal IP + IPSEC. Even when your phone is connected to Wi-Fi, it enters a special mode called IWLAN which powers your Wi-Fi calling, SMS, and RCS. The only actual factor here is if the ISP that you have versus your mobile network has a good peering.

No, in this case the consumer femtocells on the market (AT&T Cell Booster, Verizon LTE Network Extender) are actual eNodeBs inside the carrier’s RAN. They will IPSEC tunnel back to a security gateway (SeGW), grab provisioning information, and then come up on the carrier’s commercial license as just another (fancy low powered) LTE radio on the network.

AT&T did try to add some additional tamper switches and protection inside their units so they’d brick if you opened them - that was known since the MicroCell era. I believe T-Mobile’s former CellSpots were also tamper-protected in the same manner (they both deployed Nokia LTE small cells).

AT&T also appears to now charge you for the privilege of deploying the newer Cell Booster Pros if you want 5G - I assume that cost ($30/mo per cell!) is basically covering licensing the backend for all of that.

Wi-Fi Calling uses a different SeGW endpoint and is pure IMS back to the carrier voice network, regardless if you shoot it over WiFi or back over a dedicated APN on the LTE network in the normal VoLTE fare.

Thanks for adding some information on this, I had almost forgot about these devices.

So would a cell booster / network extender using eNodeBS ( https://en.wikipedia.org/wiki/ENodeB ) actually help in the scenario in the original article?

Or would it end up as the same issue with wifi calling, where "messages from 5 digit shortcodes often aren't supported over wifi calling" ?

Thanks for injecting some hard facts into this. Too many folks don't understand the difference.

If the device is remotely managed and all IPSEC back to the carrier, who cares what network it's on? At worst you'd just get poor connectivity, I don't think there's any additional exposure here.

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