Explanation: Connecting a PC to the LAN interface of an Inmarsat terminal involves standard network connectivity. TCP/IP (Transmission Control Protocol/Internet Protocol) is the fundamental protocol suite for the internet and most local area networks (LANs). A PC uses TCP/IP to communicate over its network interface, and an Inmarsat terminal, when providing internet or network access, will present a standard IP-based LAN interface. This allows the PC to access services and data through the satellite link, using the universally accepted language of the internet. ISDN is a legacy circuit-switched telephone network technology, not a LAN protocol. SMTP (Simple Mail Transfer Protocol) and FTP (File Transfer Protocol) are application-layer protocols used for specific tasks (email and file transfer, respectively) that run *over* TCP/IP, rather than being the underlying network connection protocol itself.