ISDN Protocol Administrator's and Developer's Guide ... - Intervoice

Supplementary ServicesSupplementary services are any additional ISDN functionalities that areprovided outside the original ITU-T Q.931 specification.Supplementary services can include call transfer services that arespecific to a protocol. They can also define a sequence of events thatmust occur by using standard ISDN messages and informationelements.Supplementary services also can use newly-defined informationelements or message types to provide associated ISDN services.Many modern supplementary services are defined with a standardmodeling language known as ASN.1. When encoding an ISDN messagewith an ASN.1 model, vendors have the option of encoding object IDsthat define various services within the service with either:• A unique object identifier tag• An integer tagSupplementary services that are specific to DPNSS 1 are discussed onpage 6-5.2-10 ISDN Protocol Administrator’s and Developer’s Guide 60001262, First Edition