in the realm of telecommunicationsThat's a mighty big field, and includes legacy switching and transmission 'systems' (like copper incl POTS thru to modern fiber control by SS7 protocol) as well as cellular (several varieties of technology in the US now incl GSM, GPRS, WCDMA, CDMA200) and now TCP/IP networks.
Loosen those boot strings _Jim, they're cutting off the blood supply to your brain already.