Ensuring Compliant SDP Management for P-Early Media Call Flows

In some call flows, the Oracle® Enterprise Session Border Controller (E-SBC) erroneously inserts SDP into messaging that was already set up for P-Early Media (PEM), causing unexpected media behavior. You can configure the sip-config with the strip-restored-sdp option to prevent this insertion under certain conditions and avoid subsequent signaling conflicts.

The E-SBC complies with RFC 5009 to support PEM management of media for all modes and directions. The E-SBC also includes a function wherein it stores SDP from early dialog messages so it can insert that SDP into subsequent signaling. It does this to maintain continuity for those sessions' media. Within some PEM sequences, however, the E-SBC updates the media flow with directions from the p-early-media header even without SDP in the message.

Problem behaviors avoided by configuring the sip-config with the strip-restored-sdp option include:

• If an incoming response includes a 18x and has a PEM header with the valid attribute P-Early-Media:inactive, even if there is no SDP body, the E-SBC default behavior restores the previously received SDP and updates the media flow based on the value of the restored PEM header causing conflicts with the new PEM header.
• If a final response to an INVITE arrives without SDP, and if the state of early media is not sendrecv due to a of previously received PEM header, the E-SBC default behavior creates a 1-way MBCD flow by restoring the previously received SDP, resulting in 1-way audio.

For these examples, the E-SBC needs to remove the restored SDP before it forwards the message. To remove this SDP in the cases described above, configure the sip-config with the strip-restored-sdp option using the following syntax.

ORACLE(sip-config)# options + strip-restored-sdp

Be careful to consider all the consequences of this configuration prior to deployment as it generates a global change.