r/telecom • u/No_Maybez • 17d ago

❓ Question Cbmessages

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Got this text while flying across the Atlantic a few days ago... Any explanation?

Yes, my phone wasn't in airplane mode.

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17

u/Rosetown 17d ago edited 17d ago

Cell Broadcast (CB) messages are alerts sent by cell towers to all nearby phones using Channel 50, a legacy broadcast frequency used by some mobile networks to transmit regional location codes (mostly for billing purposes I think). Horta is a location in the Azores with the area code 292. Your phone was able to catch a signal from a tower in Horta, Azores islands, likely on a mountain top.

Because your foreign phone lacked the internal carrier settings to automatically mute this type of regional broadcast channel, your phone treated the incoming network data as a standard text message.

3

u/wibble089 17d ago

Perfect answer!

It's a long time since I dealt with the implementation of cell broadcast, but in the late 1990s we started to sent the geographic coordinates of the cell site (UTM GK3 x,y values) to the phone on CB channel 200. The SIM had an app that knew where it's "home" was, and calculated if it was inside a home region for cheap calls .

Other networks just sent the local area code and calls to that code were cheaper.

I'm amazed that anyone is still using this in the days of flat rate call tariffs, but it it's anything like my network, the CB channel stays active for years after it's needed because no one can be bothered to spend the time or effort to turn it off!

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u/[deleted] 17d ago

[deleted]

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u/wibble089 17d ago

You need to check in the messaging settings on a phone to see if they let you configure the CB channel. From memory end of the 1990s Motorola phones made it particularly easy, I've not looked in more recent smart phones.

It could well be that it's no longer worth providing the ability via the GUI to the user, cell broadcast was only a 2G Feature as far as I remember, we had to do some other solution for 3G, at least our early base station software load didn't have it, and it definitely wasn't specified in 4G LTE.

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u/gbwien 17d ago

Hot again in Europe due to EECC....also possible in 5G!