uthenti- cation, data integrity and confidentiality, and privacy of client identity. The current Design and Implementation of an IMS-Based Testbed Improved IMS architecture P-CSCF I-CSCF S-CSCF Mw : SIP-reference point among different CSCFs Cx : Reference point for S-CSCF and I-CSCF to acquire information from HSS and SECS, in which the employed protocol is the diameter protocol Zb : Security interface in 3GPP network domain security PKI : Public key infrastructure AS : Application server Figure 9.3 Authentication and data security server. IMS security standards only address two technical specifications, namely access security [17] and network domain security [18]. Access security is concerned with the mutual authentication between the client and the IMS core via the IMS Authentication and Key Agreement (AKA) protocol [19]. Access security is also concerned with securing the first hop signaling between the client and P-CSCF through the security features of the SIP protocol. Network-domain security is con- cerned with providing security within the network domain for communications between the IMS components, namely HSS and the P-CSCF, I-CSCF and S-CSCF via the Cx interface. However, both access security and network domain security do not address the security of the applications and services provided. Our security service can provide secure video multicast service using the IMS architecture, the video multicast service can request for the group key management and data confi- dentiality service from the security server. The group key management service will generate a secure group key that will be used by the video server to encrypt the video data before multicast and by the IMS-based clients to decrypt the received video data (i.e., to provide data confidentiality). The group key management service will also ensure that the group key is changed whenever new IMS-based clients join the secure video multicast group or whenever clients leave the secure video multi- cast group. This ensures that new clients are not able