Question: Under what circumstances can a node set the SEID to '0' in the PFCP header of a response message when receiving a request with a protocol error, as per PFCP guidelines?
Option 1: Always, as a mandatory requirement to indicate a protocol error.
Option 2: As an implementation option, but only if the cause value is not set to 'Session context not found'.
Option 3: Never, the node must always look up and set the remote peer's SEID in response messages for protocol errors.
Option 4: Only when the request message's SEID is already set to '0'.
Explanation: According to PFCP guidelines, a node encountering a protocol error in a request may choose not to look up the remote peer's SEID and set the response SEID to '0', provided the cause value isn't 'Session context not found', showing nuanced error handling based on specific conditions.