Overview
You primarily use a home realm when using the SIP NAT function to connect multiple realms/networks to the Oracle® Enterprise Session Border Controller. You define the home realm defined as either public or private for the purposes of using the SIP NAT function. If the home realm is public, all external realms are considered private. If the home realm is private, all external networks are considered public. Usually the home realm is public.
Messages are encoded (for example, the topology is hidden) when they pass from a private to a public realm. Messages are decoded when the pass from a public realm to a private realm.
These external realms/networks might have overlapping address spaces. Because SIP messages contain IP addresses, but no layer 2 identification (such as a VLAN tag), the SIP proxy must use a single global address space to prevent confusing duplicate IP addresses in SIP URIs from different realms.