Question: During IMS registration, how does a User Equipment (UE) discover if the IMS network supports IMS data channel capability?
Option 1: By receiving a Feature-Caps header field in the 200 OK response to the initial or subsequent REGISTER request.
Option 2: Through a separate query message sent to the S-CSCF after successful registration.
Option 3: By analyzing the media feature tags in the SDP offer of the initial INVITE request.
Option 4: It is always assumed the network supports IMS data channel if the UE does.
Explanation: The correct answer highlights the specific mechanism defined for capability negotiation. When a UE registers with an IMS network and includes its media feature tag in the REGISTER request, the network responds with its capabilities. If the IMS network supports IMS data channel, it informs the UE by including a Feature-Caps header field in the 200 OK response to the REGISTER request, ensuring both parties are aware of each other's capabilities.