Global System for Mobile communications.  Digital standard operational in Europe, Middle East, Africa, Asia-Pacific region, Australia.  Uses 900 MHz frequency band.  TDMA/FDM multiple access method.  FDD duplex method.  124 channels (8 users per channel).  GSM network components are standardized.  Uses advanced encryption, Subscriber Identity Module card (smart card), supports short message service, data/fax transmission at 9.6kbit/s.
A node which allows two networks to interconnect.  For example, to connect the PSTN to a GSM PLMN.