In addition to the more than 180 ONA services [9], ESPs continue to articulate their needs for new or expanded services to the carriers in various ONA forums.
As the result of ONA requirements, a wide range of services, including basic voice service, data services, and enhanced voice storage and retrieval services are available today. The current telecommunications environment has been characterized as one with: a large number of features; multi-media, multi-party services; partial knowledge of the feature set by service designers; lower skill and knowledge levels of some service creators; multiple execution environments from different vendors; and distributed intelligence [15]. As the number of ONA services increases along with the complexity of these services, the potential for vulnerabilities associated with ONA services also increases.
Section 
provides a general description of
ONA services. Section describes specific
ONA services that have a more direct impact on NS/EP.