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Comment by jws | Hacker News Reader

Not that the telcos aren't plundering the citizens, but the SMS messages do travel in a special channel that let's you get them in a timely manner without killing your battery. It has rather small bandwidth compared to the entire cell, and that scarcity for premium functionality should cost more.

That said, AT&T takes so long to deliver a text between my family that they may as well just poll infrequently in the regular channels.

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Scarcity? What? Text messages are sent using idle channels that are not busy at the moment. It's only a scarce resource in the case that the available channels become saturated, in which case the provider has no qualms about simply dropping your text message.

You're misinformed about the channels that are used. It's actually the control channels that carry the SMS messages (the channels used for association to towers) not the voice channels. These channels can easily become heavily utilized with a large number of connected calls or devices associated to a single tower. Additionally, the message isn't dropped, it's instead queued for later delivery which typically occurs when your device migrates to a different tower.

There's some talk of SMS over GPRS. I have no idea how widely that is deployed though.

Text messages are sent in the signaling channel, this is the channel that tells your cell phone it has a call and other stuff interesting only to telephones. The advantage here is your phone is always listening to that channel.

SMS is sent during idle spots in that channel, but it is a very limited channel and you couldn't run large amounts of data through it, there just isn't enough idle time.

Scarce idle time sounds oxymoronic, but it is only idle in the sense that it isn't connecting and disconnecting phone calls.

In many installations it was very well possible to take down entire cell by mobile terminated short message traffic, which is fact that is highly inconsistent with this "idle channel theory". The GSM signaling infrastructure is not especially suited to reordering and queuing of signaling frames. The scarce resource here is time on PCH (MT case) or RACH (MO case, which is more significant as contention there can waste resources even more), actual data transfer transaction is relatively expensive (and not-so well designed), but comparable in resource consumption to initial allocation of used SDCCH. By the way, it's interesting to note that source and destination addresses of SMS can be larger than it's payload.

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