Nested Realms
Configuring nested realms allows you to create backbone VPN separation for signaling and media. This means that you can put signaling and media on separate network interfaces, that the signaling and media VPN can have different address spaces, and that the parent realm has one media-only sub-realm.
The following figure shows the network architecture.
In addition, you can achieve enhanced scalability by using a shared service interface. A single service address is shared across many customers/peers, customer specific policies for bandwidth use and access control are preserved, and you can achieve fine-grained policy control.
These benefits are achieved when you configure these types of realms:
- Realm group—A hierarchical nesting of realms identified by the name of the highest order realm.
- Controlling realm—A realms for which a signaling interface is configured. For example, you might configure these signaling interfaces in the following configurations: SIP-NAT, SIP port or H.323 stack. Typically, this is the highest order realm for the parent realm in a realm group.
- Parent realm—A realm that has one or more child realms. A parent realm might also be the child realm of another realm group.
- Child realm—A realm that is associated with a single higher order parent realm. A child might also be the parent realm of another realm group. Child realms inherit all signaling and steering ports from higher order realms.
- Media-only realm—A realm for which there is no configured signaling interface directly associated. Media-only realms are nested within higher order realms.
As these definitions suggest, parent and child realms can be constructed so that there are multiple nesting levels. Lower order realms inherit the traits of the realms above them, including: signaling service interfaces, session translation tables, and steering pools.
Since realms inherit the traits of the realms above them in the hierarchy, you will probably want to map what realms should be parents and children before you start configuring them. These relationships are constructed through one parameter in the realm configuration that identifies the parent realm for the configuration. If you specify a parent realm, then the realm you are configuring becomes a child realm subject to the configured parameters you have established for that parent. And since parent realms can themselves be children of other realm, it is important that you construct these relationships with care.
