About the Egress Realm
An egress realm allows SIP signaling to travel out of the Oracle® Enterprise Session Border Controller through a network other than the home realm. The Oracle® Enterprise Session Border Controller uses egress realms for signaling purposes (when matching flows). When a packet arrives at the Oracle® Enterprise Session Border Controller with a destination address that does not match any defined session agents, the Oracle® Enterprise Session Border Controller uses the address associated with the realm that is, in turn, associated with the SIP configuration’s egress realm ID, as the outgoing network. With the use of the egress realm ID, it is possible to define a default route for SIP requests addressed to destinations outside the home realm. If no egress realm is defined, the home realm (default ingress realm) is used as the default egress realm.
With session agent egress realm configured, the Oracle® Enterprise Session Border Controller adds a default egress realm to the session agent to identify the signaling interface used for ping requests. The Oracle® Enterprise Session Border Controller also uses the default egress realm when the normal routing request does not yield an egress realm—for example, when a local policy does not specify the next hop’s realm.
When you configure session agents, you can define them without realms or you can wildcard the realm value. These are global session agents, and multiple signaling interfaces can reach them. Then, when you use session agent pinging, the Oracle® Enterprise Session Border Controller sends out ping requests using the signaling interface of the default egress realm defined in the global SIP configuration. The global session agents in certain environments can cause problems when multiple global session agents residing in multiple networks, some of which might not be reachable using the default SIP interface egress realm.
The Oracle® Enterprise Session Border Controller uses the session agent egress realm for ping messages even when the session agent has a realm defined. For normal request routing, the Oracle® Enterprise Session Border Controller uses the egress realm for global session agents when local policies or SIP-NAT bridge configurations do not point to an egress realm.