ISO IEC 21408:2003 pdf download – Information technology — Telecommunications and information exchange between systems — Private Integrated Services Network — Inter-exchange signalling protocol — Simple dialog supplementary service. 6 Signalling protocol for the support of SS-SD 6.1 SS-SD description SS-SD enables two users to communicate via the exchange of display and keypad information. The Server User is the user who exclusively sends the display information. The user who receives that information and who is able to answer the Server User with keypad information is called the Client User. SS-SD shall be exclusively used to convey display information and keypad...