Egress Policy

The Oracle® Enterprise Session Border Controller (E-SBC) applies the egress codec policy to the SDP that was processed by the ingress policy. The E-SBC applies the egress policy the SDP exits the system into the egress realm. When no egress codec policy is defined, or the SDP’s m= lines are disabled (with a 0 port), the SDP is passed untouched from the ingress policy into the egress network.

The egress codec policy first removes all disallowed codecs in the allow-codecs parameter (<codec>:no). Codecs on the add-codecs-on-egress list are not removed from the egress policy regardless of the how the allow-codecs parameter is configured. If the result does not contain any non-signaling codecs, the ptime attribute is removed from the SDP. Codecs not present in O1 that are configured in the add-codecs-on-egress parameter are added to the SDP, only when O1 contains one or more transcodable codecs.

Note:

Transcoding can only occur for a call if you have configured the add-codecs-on-egress parameter in an egress codec policy.

If codecs with dynamic payload types (those between 96 and 127, inclusive) are added to the SDP, the lowest unused payload number in this range is used for the added codec.

The following rules are also applied for egress policy processing:

When O1 contains at least one transcodable codec the system adds the codecs listed in the Egress policy to the SDP, as follows.

• telephone-event—added only when O1contains at least one DTMF-suppported codec.
• comfort-noise—added only when O1 contains at least one non-signaling transcodable audio codec, and when O2 contains a comfort noise interoperable codec (either present in O1 and allowed, or also added on egress).
• T.38—added when there is no T.38 and there is at least one FAX-supported codec (G711Fall Back (FB)) in O1. T.38 added as a new m= image line to the end of SDP.

  When the egress policy does not allow G711FB, the E-SBC disables the m= line with the FAX-supported codec. Otherwise when G711FB is allowed; pass it through the regular offer processing allowing/adding only FAX-supported codecs.

• G711FB, added when there is no G711FB and there is T.38 in O1. The system adds G711FB as a new m= audio line to the end of SDP.

  When the egress policy does not allow T.38, the E-SBC disables the m= image line. Otherwise if T.38 is allowed, passing it through the regular offer processing.

When the result of the egress policy does not contain any non-signaling codecs (audio or video), the m= line is disabled by setting the port number to 0.

The m= line—ordered according to rules for the order-codecs parameter.

All attributes, a= lines, ptime attribute, and all other unrecognized attributes are maintained from O1. Appropriate attributes for codecs added by the add-on-egress parameter are added to SDP. The rtpmap and fmtp parameters are retained for codecs not removed from the original offer. The result is O2, as shown in the overview diagram.

You can use codec policies to normalize codecs and packetizationtime in the core realm, where the network conditions are clearly defined.

You can also use codec policies to force the most bandwidth-conserving codecs anywhere in the network.