Question: What is the primary purpose of using service primitives to describe a layer service in mobile radio interface protocols, such as those for Point-to-Point Short Message Service (SMS)?
Option 1: To constrain the implementation details of interacting entities and their interfaces.
Option 2: To capture only the essential aspects of interaction between entities relevant to the layer service itself.
Option 3: To align strictly with the formal description method of the ISO reference model for Open Systems Interconnection (ISO 7498).
Option 4: To define the general syntax for all primitives across different 3GPP Technical Specifications.
Explanation: Service primitives are used to abstract and focus on the key interactions between entities that pertain specifically to the layer service, without delving into implementation specifics. This approach helps in maintaining a clear, high-level view of the service's functionality, as seen in the context of SMS support on mobile radio interfaces.