The IMS: IP Multimedia Concepts And Services, Second Edition

19.3. Message processing

Each Diameter node maintains a Diameter peer table, which contains a list of known peers and their corresponding properties. Each peer table entry is associated with an identity and can either be statically or dynamically assigned. Dynamically assigned peer entries have an expiration time associated with them, within which they are either refreshed or discarded. Each peer entry also includes a relative priority setting, which specifies the role of the peer as either primary, secondary or alternative. The status of the peer relates to a specific configuration of a Finite State Machine (FSM) of a peer connection, called the Diameter Peer State Machine. Each peer entry also specifies whether a peer supports TLS^[] and, optionally, includes other security information (e.g., cryptographic keys and certificates).

^[] Support for IPsec is mandatory for all nodes in Diameter, whereas support for TLS is optional for clients.

Diameter peer table entries are referenced by a Diameter realm-routing table, as part of the message-routing process. All realm-based routing look-ups are performed against a realm-routing table. The realm-routing table lists the supported realms (with each route entry containing certain routing information). Each route entry is either statically assigned or dynamically discovered. Dynamic entries are always associated with an expiry time. A route entry is also associated with an application identifier, which enables route entries to have a different ...