The scope of this Technical Specification is limited to authentication of network elements, which are using NDS/IP or TLS, and to Certificate Enrolment for Base Stations as described in the present document. In the case of NDS/IP this specification includes both the authentication of Security Gateways (SEG) at the corresponding Za-interfaces and the authentication between NEs and between NEs and SEGs at the Zb-interface. Authentication of end entities (i.e. NEs and SEGs) in the intra-operator domain is considered an internal issue for operators. This is quite much in line with [1] which states that only Za is mandatory and that the security domain operator can decide if the Zb-interface is deployed or not, as the Zb-interface is optional for implementation. Validity of certificates may be restricted to the operator’s domain in case of Zb interface or in case of Za-interface between two security domains of the same operator.