Question: What happens when a mobile station supporting multicall indicates an existing Stream Identifier (SI) value in the SETUP message during a mobile originating call establishment?
Option 1: A new traffic channel is assigned to the mobile originating call.
Option 2: The indicated traffic channel shall be used for the mobile originating call.
Option 3: The network initiates a new assignment procedure to assign an appropriate traffic channel.
Option 4: The call control entity state is changed, and the call control timer is affected.
Explanation: According to the specification, when a mobile station supporting multicall indicates an existing SI value in the SETUP message, the indicated traffic channel shall be used for the mobile originating call. This ensures that the same traffic channel is reused for the ongoing call, maintaining continuity and efficiency in the communication process.