ETSI TS 187 021 specifies the functional models and information flows (stage 2) and protocols (stage 3) which implement the security services and mechanisms required to provide security in a Customer Premises Network (CPN) to support the overall security architecture for NGN release 3. CPN security services and mechanisms are used either singly or in combination to realize the CPN security requirements specified in TS 187 001 [1] (NGN Security requirements). Reference will be made to TR 185 012 [i.1] for security mechanisms that have been shown to be appropriate for CPN environment.