Fundamental Diameter Concepts and Building Blocks

This chapter covers the basic concepts of Diameter, describing the types of nodes that participate in Diameter sessions and the format of Diameter messages. It also provides an overview of Diameter sessions and error handling. Diameter is a flexible, extensible protocol. The base protocol specifies only a basic accounting application, but provides building blocks for creating new applications that can address the particulars of authentication, authorization, and/or accounting for various networks. When Diameter messages are transmitted between nodes, they are transmitted in network byte order, that is, with the most significant byte sent first. A session, which is related to the service provided to an end user, is a sequence of related Diameter messages and is a logical concept at the application layer. In order to provide failover support, all agents maintain a transaction state by saving the request's unique identifier, known as a Hop-by-Hop Identifier, which is designed to match answers with requests.