The IMS: IP Multimedia Concepts And Services, Second Edition

19.7. Error handling

Diameter errors fall into two categories: protocol errors and application errors. Protocol errors occur at the base protocol level and are treated on a per-hop basis (e.g., errors in message routing may direct a downstream agent to take special action). Application errors are generated due to problems with specific Diameter applications.

When a request message generates a protocol error an answer message is sent back with the "E" bit set in the Diameter header, indicating a protocol error. The appropriate protocol error value is then placed in a Result-Code AVP in the answer message. On the other hand, when a Diameter entity generates an application error it sends back an answer message with the appropriate Result-Code AVP included. Since application errors do not require any Diameter agent involvement, the message is forwarded directly back to the originator of the request.

Table 19.2 describes the classes used in the Result-Code AVP data field: a 32-bit namespace for errors, maintained by IANA. The Result-Code AVP can also be accompanied by other elements that give additional information about the error message (e.g., a human-readable error message must be included for all protocol errors in an Error-Message AVP).