FOSS in the Mobile World
GSM Network Architecture

GSM is a bit-synchronous network
it draws many analogies from ISDN and SDN
layer 2 modelled after Q.921 / LAPD
call signalling modelled Q.931
but: many more protocols for mobility management, radio resources, ...
like all traditional Telco protocols: Intelligence in the network, not in the end nodes.

GSM is a TDMA "nightmare"
e.g. you never know from/for whom data is without the timing context