Bluetooth allows 7 devices connected at once, but actually the spec uses bluetooth low energy which is a special low-bandwidth, low-energy mode. You can lock your device. [1]
It sounds to me like NHS wants location data logs of everyone in the country. You can measure contacts and spread that way but it's a privacy disaster. The decentralized approach tells authorities and users if they've been near someone who later on marked themselves as infected. The data is much more limited but still accomplishes the main purpose.
There is no BLE hard limit to device connections here at all.
This whole system works on advertising packets. Beacons are non-connectable, aptly named.
Your phone can be connected n number of BLE devices and also appear to be n number of peripherals itself. No hard limit that I can think of, usually just depends on the stack.
But this isn’t that. This is your phone pumping out <CONTACT: I am 7733> and listening for other people’s phones to say <CONTACT: I am xxxx>.
I can think of no stack that has a connection limit and after that stops allowing for reception of advertising packets.
Nitpicky clarification: at least for the Apple/Google spec it's advertising something more like "my key for the current 15-minute timespan is 7733". ie, not your identity, just a temporary key.
I believe that Bluetooth units are limited to 1 central (master/server/upstream) and 7 peripheral (slave/client/downstream) connections. Mesh networks can be made up of up to 255 units.
Advertising is different, and not limited, but it is not classified as a 'connection'. My understanding is that advertisements are simply broadcast, so there is no bidirectional communication.
I thought I had seen multi master stacks. For peripherals I know I’ve seen 20 concurrent this n the Nordic S132, definitely not 8 as any BLE spec limitation.
Yes. That’s what I said, beacons are advertising packeting with the connectable flag cleared.
You misunderstood, there is no bidirectional in my post. Just two transmitters and two receivers.
Yeah this doesn't actually connect to devices so the limit of 7 doesn't apply. Your phone just broadcasts an advertising beacon (exactly the same as iBeacon or Eddystone) and other phones listen for it.
It's easy to do on Android (though somewhat unreliable because the Android Bluetooth stack is utter shite).
On iOS it is more tricky, but as I recall it is possible if your app has a widget on the home screen. This is what Chrome has to do for the physical web:
It sounds to me like NHS wants location data logs of everyone in the country.
How are they going to get that with either model being discussed? There is no location data being transmitted. In fact there is no data at all leaving the phone until you get ill. And if they could deduce it from some sophisticated analysis of codes sent and matched, it would be far, far easier from the geolocation data users happily donate to Google/Apple free-of-charge 24/7.
Location is not the really interesting thing - the social graph is. Location is interesting because it reveals the social graph, not the other way around.
> In fact there is no data at all leaving the phone until you get ill.
Source? Everything I found that could be interpreted as a statement in that direction sounded like it was part of a description of the Apple-Google approach.
In particular, I wonder if the APIs exposed to non-system apps let them rotate the Bluetooth identifiers, of if this will cause the phones to beacon their non-randomized Bluetooth equivalent of a MAC address nonstop. (The Apple-Google proposal covered this by randomizing that address too.)
It sounds to me like NHS wants location data logs of everyone in the country. You can measure contacts and spread that way but it's a privacy disaster. The decentralized approach tells authorities and users if they've been near someone who later on marked themselves as infected. The data is much more limited but still accomplishes the main purpose.
[1] https://covid19-static.cdn-apple.com/applications/covid19/cu...