Question: What is the condition for the 5G system to support mechanisms to enable traffic steering and/or switching of a DualSteer device's user data across two 3GPP access networks belonging to two PLMNs?
Option 1: The HPLMN policy and network control must be in place, but there is no need for a business/roaming agreement between PLMN operators.
Option 2: A business/roaming agreement between PLMN operators (if different) must be in place, but the HPLMN policy and network control are not required.
Option 3: The DualSteer device must support simultaneous transmission over the two networks.
Option 4: A business/roaming agreement between PLMN operators (if different) must be in place, and the HPLMN policy and network control must also be in place.
Explanation: According to the text, subject to HPLMN policy and network control, the 5G system shall be able to support mechanisms to enable traffic steering and/or switching of a DualSteer device's user data across two 3GPP access networks belonging to two PLMNs, assuming a business/roaming agreement between PLMN operators (if different). This indicates that both conditions are necessary for the 5G system to support this functionality.