Egress Policy

The Oracle® Enterprise Session Border Controller applies egress codec policy to the SDP that has already been processed by ingress policy. The egress policy is applied before the SDP exits the system into the egress realm. If 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 un-allowed 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 if 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:

If O1 contains at least one transcodable codec, the codecs listed in the Egress policy are added to the SDP.

• telephone-event, as configured in add-codecs-on-egress will only be added if O1contains at least one DTMFable codec.
• T.38, as configured in add-codecs-on-egress will only be added if there is no T.38 and there is at least one FAXable codec (G711Fall Back (FB)) in O1. T.38 will then be added as a new m= image line to the end of SDP.

  If G711FB is not allowed in the egress policy, the Oracle® Enterprise Session Border Controller disables the m= line with the FAXable codec. Otherwise if G711FB is allowed, pass it through the regular offer processing allowing/adding only FAXable codecs.

• G711FB, as configured in add-codecs-on-egress will only be added if there is no G711FB and there is T.38 in O1. G711FB will then be added as a new m= audio line to the end of SDP.

  If T.38 is not allowed in the egress policy, the Oracle® Enterprise Session Border Controller disables the m= image line. Otherwise if T.38 is allowed, pass it through the regular offer processing.

If 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 is next ordered according to rules for the order-codecs parameter.

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

In practical terms, codec policies can be used to normalize codecs and ptime in the core realm where the network conditions are clearly defined.

Codec policies can also be used to force the most bandwidth-conserving codecs anywhere in the network.