This paper presents the design and implementation of WIRE Diameter. The WIRE Diameter is an open source implementation of Diameter Based Protocol and Diameter EAP Application developed by the Wireless Internet Research & Engineering (WIRE) Laboratory. Research has shown that traditional RADIUS protocol may suffer performance degradation and data loss in a large system. Diameter, thus, was proposed to address the deficiencies in RADIUS. Both 3GPP and 3GPP2 have adopted Diameter as their AAA protocol. The WIRE Diameter could be used to authenticate and authorize 802.1x supplicant It provides various authentication schemes, including EAP-MD5, EAP-TLS, EAP-TTLS, and PEAP. The WIRE Diameter is developed to be independent of OS as much as possible. Currently it supports Linux, FreeBSD and various versions of MS Windows. It is believed that the WIRE Diameter is the first open source implementation of Diameter EAP Application in the world. The source code can be downloaded freely. The WIRE Diameter should be useful for the research community. This paper demonstrates the B design and implementation of the WIRE Diameter.