Question: For an RNC/CN-node supporting IP transport on the Iu interface with low bandwidth PPP links (e.g., E1/T1/J1), what additional protocol must be supported to optimize bandwidth usage?
Option 1: MPLS (Multiprotocol Label Switching) for enhanced routing
Option 2: IP Header Compression (as per IETF RFC 2507) with negotiation via IETF RFC 2509
Option 3: ATM (Asynchronous Transfer Mode) Adaptation Layer 5 (AAL5) for cell transport
Option 4: Ethernet Frame Relay for packet switching
Explanation: In the context of low bandwidth PPP links on the Iu interface, IP Header Compression is crucial for optimizing bandwidth usage. This is achieved through supporting IP Header Compression, ensuring efficient use of limited bandwidth resources in UTRAN networks.