Identifier of senders and receivers of telegrams. A technical identifier uniquely identifies a EULYNX subsystem or an adjacent system. The schema is [country code][area designator][system type][code][tag][sequence no] E.g. A Subsystem - Generic IO 5 in Germany in area HG2_X in operating location 37 has the identifier: DEHG2_XIO___37##0005. Also known as SubS_ID.