Overview

Without adaptive HNT, the Oracle® Enterprise Session Border Controller keeps NAT pinholes open and port mapping cached by forcing the UAC to send frequent SIP REGISTER messages. It does so by setting the expires time to a short interval. Some NATs only need a message to be sent by the private client once every twenty minutes, while other NATs delete their cache/pinhole in thirty seconds if no messages appear. Given this large variation in time intervals, the Oracle® Enterprise Session Border Controller’s nat-interval (expire time) has been set to a low value in order to support as many NAT types as possible. However, CPU performance and scalability issues result from such a small refresh time, especially when there is a very large number of potential registered users.

When you use adaptive HNT, the Oracle® Enterprise Session Border Controller waits for a time interval and then sends a SIP OPTIONS message to the UAC to see if it can still be reached. If the UAC can still be reached, the Oracle® Enterprise Session Border Controller increases the timer and tries again. In case the pinhole closes because it has exceeded the NAT's cache time, the Oracle® Enterprise Session Border Controller sets the expires time to be slightly longer than the time it tests using the OPTIONS method. This way, the UAC will send another REGISTER message shortly thereafter and impact on service will be minimal.