Prerequisites

In order to achieve HNT, the endpoints involved must be capable of:

• symmetric signaling: sending and receiving SIP messages from the same transport address (IP address or User Datagram Protocol/Transmission Control Protocol (UDP/TCP) port
• symmetric media: sending and receiving Real-Time Transport Protocol (RTP) messages from the same UDP port

These conditions are required to allow signaling and media packets back through the NAT (through the bound external address and port). These packets must come from the address and port to which the outbound packet that created the NAT binding was sent. The NAT sends these inbound packets to the source address and port of the original outbound packet.

When SIP HNT is used, the Oracle® Enterprise Session Border Controller sends signaling responses to the address and port that the request came from rather than the address and port indicated in the request. The Via header in the request message indicates where the response should be sent.