sub addressing (SUB)

Sub-addressing (SUB) is an ISDN or GSM feature that allows the addressing capacity to be extended beyond the ISDN call number. With sub-addressing, additional information is transmitted from the calling party to the recipient when the connection is set up; a total of max. 20 bytes. Since the network does not handle the sub- address and transmits it transparently, this message can be freely designed by the recipient. The subaddressing can be used to perform certain procedures such as calling a specific program.