I am studying for SMS PDU.
However, I do not know why the SMS PDU transmits the phone number and the like by reverse nibbled. (012345 to 103254)
Why does it work like this?
Noone knows excactly :) But in telco within SS7 protocol, almost all numbers are reversed (vlr,hlr,imsi etc.) In older days on slow networking, every bit matters, thats why SS7 is so optimized. I believe it has to do with a speed when number has odd length. In newer protocols (like Volte) there is no such thing anymore.