This Technical Report defines the functions that are performed by, and the requirements for the Data Border Function (DBF) within a Service Provider?s network. Informative details on implementation realizations of a DBF are also provided. A DBF is comprised of a set of Session Security Functions together with Authentication and Proxy (A/P) functions. The separation of the DBF into its component functions is described, and session control, A/p, and OAM&P requirements are provided. In additional, the Data Border Function is mapped into the ATIS Next Generation Network (NGN) Architecture (described in ATIS-1000018).