Diameter Peers

Capabilities Exchange

The first Diameter messages exchanged between two Diameter peers, after establishing the transport connection, are Capabilities Exchange messages. A Capabilities Exchange message carries a peer's identity and its capabilities (protocol version number, supported Diameter applications, etc.). A Diameter node only transmits commands to peers that have advertised support for the Diameter application associated with the given command.

Transport Failure Detection

Application-level heartbeat messages called the Device-Watchdog-Request and Device-Watchdog-Answer messages are used to proactively detect transport failures. These messages are sent periodically when a peer connection is idle and when a timely response has not been received for an outstanding request.

Failover/Failback Procedures

If a transport failure is detected with a peer, a Diameter node attempts to failover to an alternate peer, which means that all pending request messages sent to the failed peer will be forwarded to the alternate peer.

A Diameter node periodically attempts to re-establish the transport connection with a failed peer. Should a connection be re-established, a node can failback to this peer (i.e., messages can once again be forwarded to this peer).

A failover to an alternate proxy agent may result in the reception of duplicate request messages by the home server.