Question: What is a key function of the P-CSCF in NAT traversal when supporting Outbound in an IP Multimedia Subsystem (IMS), specifically regarding UE communication?
Option 1: The P-CSCF dynamically allocates new NAT bindings for each incoming dialog request to the UE.
Option 2: The P-CSCF only handles outbound requests from the UE, without processing inbound responses.
Option 3: The P-CSCF ensures all responses to the UE are sent to the same source IP address and port as the initial request, utilizing existing NAT bindings.
Option 4: The P-CSCF bypasses STUN server functionality for NAT traversal when the UE initiates multiple concurrent dialogs.
Explanation: This is correct because, according to specified behavior for NAT traversal in IMS, the P-CSCF's role includes ensuring responses to the User Equipment (UE) are directed appropriately to maintain existing NAT bindings. This involves sending responses back through the same source IP address and port from which the request was received, facilitating uninterrupted communication across the network.