Ingress Policy

Incoming SDP is first subject to the ingress codec policy. If no codec policy is specified in the realm config for the ingress realm, or the m= lines in the SDP offer are disabled (by a 0 port number), the SDP is transformed to O1 unchanged.

The ingress codec policy first removes all un-allowed codecs, as configured in the allow-codecs parameter by setting their port to 0 or removing the codecs from a shared m-line. For example, if two codecs share an m-line and one of them is un-allowed, the resulting m-line will not include the un-allowed codec and its attribute lines will be removed. If a single codec is used, the resulting m-line will include the codec, but its port will be set to 0 and its attribute lines will remain. Next, the remaining codecs are ordered with the order-codecs parameter. Ordering is when the codec policy rearranges the codecs in the SDP m= line. This is useful to suggest the codec preferences to impose within the egress realm. O1 is then processed by the egress codec policy after a realm is chosen as the destination.

In practical terms, the ingress policy can be used for filtering high-bandwidth codecs from the access realm. It can also be used for creating a suggested, prioritized list of codecs to use in the ingress realm.