Post AkWjOLnaK2L8Itn8mO by danderson@hachyderm.io
 (DIR) More posts by danderson@hachyderm.io
 (DIR) Post #AkWjOKES9AdxReLZNg by danderson@hachyderm.io
       2024-08-01T02:08:09Z
       
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       Skimming some bluetooth specs, I genuinely wonder now: if you transmit, say, 1kiB over the Mesh BLOB profile, how much total airtime and transmitted symbols does that expand to? With the amount of layering involved, I wouldn't be surprised if it's multiple megabits once you're closer to the antennas.
       
 (DIR) Post #AkWjOL4D2k2m2AYu3M by danderson@hachyderm.io
       2024-08-01T02:10:44Z
       
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       BLE is like a microcosm of microservice architecture and OSI layering. Every layer has a purpose, but every new thing runs over all the existing layers. So as you climb up the stack you go from 3MB/s on a PtP air link, to 1MB/s, to 125kB/s, to "we conspicuously don't discuss the throughput at this layer, but you get 29 bytes of payload per message."And then they build FTP on top of that.
       
 (DIR) Post #AkWjOLnaK2L8Itn8mO by danderson@hachyderm.io
       2024-08-01T02:12:41Z
       
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       From the perspective of being able to ship product quickly, it's undeniably cool. Grab a single chip solution, the associated SDK, and from peloton bikes to insulin pumps to stage lighting controls, there's an API for that.But it does make me wonder what the overhead is on "turn on light number 27".
       
 (DIR) Post #AkWjOMO68HXy88sIgy by danderson@hachyderm.io
       2024-08-01T02:22:52Z
       
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       Huh, well, according to at least one article on bluetooth dot com: less overhead than I thought. For 29 bytes of user payload, the claim is that 47 bytes get sent to the RF layer for transmission.So, 40% overhead or so. Not great, not terrible.Although that's only counting the initial transmission. This is Bluetooth Mesh, which uses broadcast flooding in lieu of routing. So, those 47 bytes may get retransmitted a significant number of times as it bounces around the mesh.
       
 (DIR) Post #AkWjOMwU4R3JqmxlI0 by danderson@hachyderm.io
       2024-08-01T02:24:09Z
       
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       Though in practice, I suspect there aren't many meshes out there taking full advantage of "up to 32k nodes" and configuring all of them as relays.
       
 (DIR) Post #AkWjONihBBcKGJWGR6 by danderson@hachyderm.io
       2024-08-01T02:32:19Z
       
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       Anyway, 400 microseconds and 40% overhead per 29-byte message, but that message comes with authenticated encryption, relaying including store-and-forward, and working multicast. That's honestly kinda neat.Pay no attention to the massive firmware blob in the baseband chipset, and pay no mind to how robustly it might have been implemented.
       
 (DIR) Post #AkWjOOExFFQBsMc1ia by tomjennings@tldr.nettime.org
       2024-08-01T15:18:36Z
       
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       @danderson This. I don't want to see my sausages being made either.