Question: What protocol, alongside Session Description Protocol (SDP), forms the basis of IP multimedia call control as per the standard referenced for UE-initiated IMS registration in E-UTRA conformance testing?
Option 1: Session Initiation Protocol (SIP)
Option 2: Diameter Protocol
Option 3: GPRS Tunneling Protocol (GTP)
Option 4: Stream Control Transmission Protocol (SCTP)
Explanation: In the context of IMS (IP Multimedia Subsystem) signalling, especially for UE-initiated actions like registration, the protocol framework is crucial. Session Initiation Protocol (SIP) is specifically designed for initiating, maintaining, and terminating real-time communication sessions, making it a foundational element for IP multimedia call control when used in conjunction with SDP for media description. This aligns with the requirements for IMS support in UEs as referenced in the telecom standards.