Question: In IMS networks, what is the primary purpose of establishing a SIP session between the invoking function and the Media Resource Function Controller (MRFC)/Media Resource Function Processor (MRFP) for media transcoding?
Option 1: To facilitate direct communication between calling and called User Equipment (UEs)
Option 2: To exchange subscriber data between the IMS control plane and external networks
Option 3: To manage Quality of Service (QoS) parameters for ongoing sessions
Option 4: To reserve resources at the transcoding unit and exchange transport address and port information
Explanation: The correct answer, Option 4, highlights the key purpose of establishing a SIP session for media transcoding in IMS networks. This process is crucial for ensuring seamless communication between UEs with incompatible terminal equipment or in error cases, by reserving necessary resources at the MRFP (the actual transcoding device) and facilitating the exchange of vital connection details. This understanding is pivotal in managing interoperability and maintaining service quality across diverse user devices within telecom networks.