SIP Via Transparency

This section explains the inbound Via header transparency feature, which enables the Oracle® Enterprise Session Border Controller to insert its Via header on top of the top-most Via header received from user equipment (UE). It then forwards it on to the IP Multimedia Subsystem (IMS) core with the original Via header now located as the bottom-most Via header.

The Oracle® Enterprise Session Border Controller still replaces the Contact and other header addresses with its own, and does not pass on the core’s Via headers in outbound requests.

This feature is targeted for the Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN) with SIP hosted NAT traversal support. It works with SIP NAT bridged, local-policy routed, and non-SIP NAT configurations, regardless of registration handling.

Some equipment acts as Proxy-CSCF (P-CSCF) and Serving-CSCF (S-CSCF) nodes, with the Oracle® Enterprise Session Border Controller is located between the equipment and user endpoints. The equipment needs to see the each user endpoint’s original Via header in order to perform some implicit authentication, admission, and control functions in a TISPAN-compliant model.

You enable Via header transparency on the access SIP interface. Received Via headers are saved for inclusion in requests going out another interface or session agent that does not have the parameter set, in other words, the core side. For any received SIP message where the inbound previous hop interface was enabled for Via header transparency, theOracle® Enterprise Session Border Controller adds its own Via header as it forwards it, and it also copies the received top-most Via as the new bottom-most Via, if the outbound next hop interface/session agent is not enabled for Via header transparency. The Oracle® Enterprise Session Border Controller also adds a received= parameter to the copied Via header, per the SIP RFC 3261.

Any message received from an interface without Via header transparency enabled, does not have the received Via header copied over to any other direction.

For HNT, where the original top-most (and only) Via header from a UE is a private/false address, the SD should still copy that false address into the core-side, and the received= parameter will contain the real Layer-3 addressing.

SIP Via Transparency Configuration

You can configure SIP Via header transparency for the access SIP interface using the ACLI.

To configure SIP Via header transparency for an access interface:

In Superuser mode, type configure terminal and press Enter.
```
ORACLE# configure terminal
```
Type session-router and press Enter to access the media-level configuration elements.
```
ORACLE(configure)# session-router
ORACLE(session-router)#
```
Type sip-interface and press Enter. The system prompt changes to let you know that you can begin configuring individual parameters.
```
ORACLE(session-router)# sip-interface
ORACLE(sip-interface)#
```
You can either add support to a new SIP interface configuration or to an existing SIP interface configuration:
For a new SIP interface configuration, you can add the option by typing options, a Space, and then via-header-transparency.
```
ORACLE(sip-interface)# options via-header-transparency
```
For an existing SIP interface configuration without options configured, select the SIP interface, type options followed by a Space, and then via-header-transparency.
```
ORACLE(sip-interface)# select
ORACLE(sip-interface)# options via-header-transparency
```
For an existing SIP interface configuration with options configured, select the SIP interface, type options followed by a Space, the plus sign (+), and the via-header-transparency option.
```
ORACLE(sip-interface)# select
ORACLE(sip-interface)# options +via-header-transparency
```
Save your work using the ACLI save or done command.