4 ms·
Did not early WhatsApp use a covert channel in sms signalling, just like you can get 2.4kb/s across the x.25 "D" channel of ISDN? I've no idea if true or not,
by amygdyl 9y ago
Did not early WhatsApp use a covert channel in sms signalling, just like you can get 2.4kb/s across the x.25 "D" channel of ISDN?
I've no idea if true or not, my memory unreliably tells me I found some kind of confirmation, but common sense tells me not to rely on such recollections.. but I often pondered if such channels exist in the GSM spec, back in the day, when I was shocked to receive a sms, the service having been given free to early subscribers in the UK, I literally had the first (edit)model Nokia GSM handset, and was most sceptical :D
- Matthias247 9y agoI think you are mixing that up: SMS uses a signaling channel of GSM. It was originally not intended to become that big and just used otherwise unused resources. Therefore it could have been given out for free or very cheap. Later on telecom providers saw that people like text messages and that it has an enormous business potential, so they started to make huge charges for it.
- TorKlingberg 9y agoThe "otherwise unused" isn't true. Any time your phone is transmitting, it is using some of available bandwidth in the air. It does go other the control channel is GSM rather than setting up a data channel, and is was originally just for testing, carrier announcements etc. The per-SMS charge is far higher than actual costs, but so is everything. Mobile networks are almost entirely fixed costs in building the network.