Question: In an MCPTT (Mission Critical Push To Talk) system, when protection of media is negotiated for an Interworking Function (IWF) performing a non-controlling role, how does the IWF handle RTP (Real-time Transport Protocol) media streams?
Option 1: The IWF encrypts and then forwards the RTP media streams.
Option 2: The IWF decrypts and then re-encrypts the RTP media streams before forwarding.
Option 3: The IWF modifies the payload of the RTP media streams for security enhancement.
Option 4: The IWF remains transparent to RTP media streams and forwards them without decrypting the payload.
Explanation: In MCPTT systems, when an Interworking Function (IWF) is in a non-controlling role and media protection is negotiated, the IWF's primary concern is secure transmission. Since media protection is already negotiated, it implies encryption has been handled prior to reaching the IWF. Therefore, to maintain integrity and confidentiality without introducing latency or overhead, the IWF should not attempt to decrypt (and thus would not re-encrypt) the RTP media streams. Instead, it remains transparent to these streams, ensuring they are forwarded in their encrypted form, preserving the security established during negotiation, aligning with efficient and secure handling of real-time communications in mission-critical scenarios.