Open Service Access

The specification, design, and implementation of services in a telecommunications
network were at one time limited to a very small pool of programmers, as services
were normally written as additional software for network elements (e.g., switches).
Even the advent of Intelligent Networks (IN) did little to improve this situation,
as a service designer still needed an intimate knowledge of telecommunications
networks and protocols.

Open service access (OSA) is an attempt to provide a much more open, yet
secure, environment for service development by abstracting the network functions
into a high-level view and providing access to these functions by means of standard,
well-defined application programming interfaces (APIs) (Figure 4.12). The work
on what is now known by some as OSA was started by the Parlay Group, which
focused on the U.K. network of British Telecom (BT), which the regulator wanted
to open up to third-party service providers. The Parlay Group works on the APIs
and the model for service providers to access the network functions.
The OSA project of the 3GPP is now aligned with Parlay, and the names are
now interchangeable. The OSA consists of an API that exposes, in an abstract manner,
the service capabilities of the network. A service designer can manipulate these
service capabilities to build innovative services (e.g., a service based on the location
of a mobile device).

A major concern for network operators is security and the security of information;
therefore, the OSA gateway that supports service providers also includes
a framework element that is responsible for authenticating service providers and
authorizing what functions (and information) that provider is able to see. Using
standard network signaling protocols such as SS7-based protocols, the OSA gateway
is able to manipulate the network elements to achieve the functions of a particular
service, although the service designer is isolated from the detail of these
protocols. The service provider in an OSA environment could be either within the
network (i.e., the network operators themselves) or a trusted third party.
Live OSA-based mobile services are available in some networks, although the
end user will not be aware that this is how the service is provided. These services
include prepay, location services, virtual private networks (VPNs), and unified
messaging (UM).