Adaptive Hosted NAT (HNT) Feature

C.

Sure, I'd be happy to explain what the Session Border Controller (SBC) does when the Adaptive Hosted NAT (HNT) feature is enabled.

The Adaptive Hosted NAT (HNT) feature is designed to address challenges with NAT traversal, which is necessary for VoIP and other real-time communications protocols to work effectively. NAT (Network Address Translation) is a technology used to allow multiple devices on a private network to share a single public IP address for communication with the Internet. However, NAT can cause problems for real-time communication protocols because it can obscure the IP addresses and port numbers used by endpoints behind the NAT device.

When the Adaptive Hosted NAT (HNT) feature is enabled on an SBC, the SBC will perform several functions to ensure that communication is able to flow between endpoints behind NAT devices:

B. It creates a binding for the Address of Record (AOR) of an endpoint that is behind a NAT.

When an endpoint behind a NAT device registers with the SBC, the SBC creates a binding between the endpoint's Address of Record (AOR) and the IP address and port number that the endpoint is using behind the NAT device. This binding allows the SBC to route incoming calls to the correct IP address and port number.

D. It sends SIP OPTIONS at increasing intervals to test if an endpoint behind a NAT device is still reachable.

The SBC sends SIP OPTIONS requests to the endpoint at increasing intervals to test whether the endpoint is still reachable. If the endpoint responds to the SIP OPTIONS request, the SBC assumes that the endpoint is still active and reachable, and it will continue to use the binding it created for the endpoint. If the endpoint does not respond to the SIP OPTIONS request, the SBC will assume that the endpoint is no longer reachable and it will remove the binding.

A. It sends a periodic re-register command to each endpoint behind a NAT.

The SBC sends periodic re-register commands to each endpoint behind a NAT device to ensure that the binding it created for the endpoint is still valid. If the endpoint responds to the re-register command, the SBC will assume that the binding is still valid and it will continue to use it. If the endpoint does not respond to the re-register command, the SBC will assume that the binding is no longer valid and it will remove it.

Therefore, the correct answers are B, D, and A.

It's worth noting that the SBC does not send ICMP PNGs (E) to dynamically learn the binding time of an endpoint behind a NAT device. ICMP PNGs are a type of network packet used for testing network connectivity and are not used by the SBC in this context.