Overview

TheOracle® Enterprise Session Border Controller is an intermediary device that provides NAT functions between two or more realms. It translates IP addresses between untrusted and trusted networks using NAT. A trusted network is inside the NAT, and a untrusted network is outside the NAT. A NAT also lets a single IP address represent a group of computers.

For SIP, the SIP NAT function on the Oracle® Enterprise Session Border Controller does the following:

routes SIP packets between the Oracle® Enterprise Session Border Controller’s SIP proxy (B2BUA) and external networks (or realms), including the translation of IP address and UDP/TCP port information.
prevents private IP addresses in SIP message URIs from traveling through the untrusted network. SIP NAT either translates the private address to one appropriate for an untrusted address or encrypts the private address into the URI.

Packets arriving on the external address (at port 5060) are forwarded to the Oracle® Enterprise Session Border Controller’s SIP proxy with the source address changed to the home address (at port 5060). When the Oracle® Enterprise Session Border Controller’s SIP proxy sends packets to the home address (at port 5060), they are forwarded to the external proxy address (and external proxy port), with the source address changed to the external address (at port 5060).

Note:

The SIP config’s NAT mode parameter works in conjunction with the SIP NAT function configuration. It identifies the type of realm in which the SIP proxy is located (public or private) and affects whether IPvr addresses in SIP messages are encoded.

The translation of URIs in the actual SIP message occurs as messages are received and sent from the Oracle® Enterprise Session Border Controller’s SIP proxy. For the messages being sent to the external network, the contents of the SIP message are examined after the translation to determine if the destination needs to be changed from the external proxy address to an address and port indicated by the SIP message. This process takes place so the request is sent to where the Request-URI or the Route header indicates, or so the response is sent to where the Via indicates.