Question: What protocol is mandated for Reference Point 3 in SMS transfer when the two end nodes are in different Public Land Mobile Networks (PLMNs), unless otherwise agreed upon bilaterally?
Option 1: PSPDN (Packet Switched Public Data Network)
Option 2: TCP/IP (Transmission Control Protocol/Internet Protocol)
Option 3: CCITT SS No. 7 (according to Mobile Application Part specification)
Option 4: HTTP (Hypertext Transfer Protocol)
Explanation: In telecommunications, when interacting between different networks (inter-PLMN), standardized protocols ensure seamless communication. For Reference Point 3 in SMS transfers across different PLMNs, CCITT SS No. 7, as specified by the Mobile Application Part (MAP) protocol, is required unless there's a bilateral agreement for an alternative. This ensures interoperability and reliable message delivery between disparate networks.