protocol was derived from RADIUS (Remote Authentication Dial In User Service) protocol with a number of improvements. This protocol is used widely in 3GPP Release 5 onwards, where there is a need for AAA services. Emerging new technologies in communication that have been built on total IP networks have shown an increased requirement for access control mechanisms more than ever due to security concerns. Therefore, Diameter protocol was developed as a framework for future AAA services with enhancements to existing RADIUS protocol. Diameter protocol was designed as peer to peer architecture even though, it looks like a server client protocol in the implementation. As per the Diameter protocol there is a node called diameter agent, which does either message relay, proxy, redirecting or translate function. Since Diameter protocol uses synchronous message exchange format, there are specific responses for each request message. It uses Attribute Value-Pairs (AVPs) to transfer these messages between nodes. Diameter uses IP networks as its medium, and runs on top of TCP (Transport Control Protocol) or SCTP (Signalling Control Transport Protocol), where it can have more reliable communication.