Interoperability is a broad and complex subject rather
than a binary attribute of systems. C4I interoperability is a key enabler for
the conduct of effective, collaborative, multi-service military operations
across a wide spectrum of scenarios, and successful conduct of operations is
the ultimate test of whether an adequate degree of interoperability is being
achieved. Joint Chiefs of Staff Publication 1-02 defines interoperability at
both the technical and operational level (Box 2.1).2 Operational interoperability
addresses support to military operations and, as such, goes beyond systems to
include people and procedures, interacting on an end-to-end basis.
Implementation of operational interoperability implies not only the
traditional approach of using standards but also enabling and assuring
activities such as testing and certification, configuration and version
management, and training. These definitions of operational interoperability
encompass the full spectrum of military operations, including
intra-service/agency, joint (inter-service/agency), and ad hoc and formal
2.1.1 What Is Interoperability?
Interoperability at the technical level (see Box 2.1) is essential to achieving operational interoperability. An issue that arises between systems rather than between organizations, technical interoperability must be considered in a variety of contexts and scopes, even for a single mission. Consider the theater missile defense mission, which is likely to require that data be:
- Exchanged among elements of a weapon system. For example, the Patriot air defense system uses a defined message format and data link to exchange information within batteries and between batteries to share target information and coordinate defensive actions.
- Exchanged between weapons systems of a single organization or service. For example, the Theater High Altitude Area Defense system (under development) will provide theater ballistic missile tracks to Patriot systems.
- Exchanged between weapons systems of different services. For example, a Navy AEGIS radar may report tracks to an Army Patriot radar.
- Shared and "pooled" at the joint task force command and control systems level (or higher) in order to achieve synergy and added value. For example, Patriot, AEGIS, and Airborne Warning and Control
System data may be combined to develop a common operating picture and to
control and coordinate all the systems sharing data.
The range of complexity of requirements for data flow in such a mission underscores the significance of interoperability at every level.
One source of interoperability problems is incompatibilities in independently selected versions (e.g., software releases) of the same system. Thus, if one unit has standardized on version A of a given system and another on version B, capabilities supported by one system and not the other may well interfere with seamless interoperation between the two units. The committee observed several such situations in its visits to exercises. Also, just as differences in modes of operation across the services can lead to non-interoperability, so can organizational differences within a service also lead to intra-service incompatibilities. One example that the committee heard about involved information security procedures and practices that were different in the U.S. Atlantic and U.S. Pacific commands, presenting difficulties for units that are reassigned from one theater to another.
When thinking about C4I it is important to understand
the distinction between joint systems and systems that are interoperable (Box
2.2). A system is designated as joint either to support an efficient buying decision for two or more services that will use it, or because the system will be subject to joint command. By contrast, to meet requirements for interoperability, services' systems must be able to share data in a timely, reliable manner that is operationally useful, and must operate across service or agency boundaries to support joint missions. Interoperability does not necessarily imply joint (multiple service) programs; interoperability can and must be achieved without jointness. Joint programs are but one of a number of management approaches for achieving interoperability of systems among the military services.
Although many view interoperability as an issue arising
in the context of two or more services (or nations), fielding a wide variety of
mature systems built with little attention to supporting joint or coalition
operations,3 in fact its sphere is broader. Indeed, during its site visits the committee heard several examples of C4I systems owned and operated by the same service that have difficulties in interoperating. For example, in one visit, the committee observed that with the Army Forward Area Air Defense Command, Control and Intelligence System and the Maneuver Control System there were difficulties in overlaying data from one system with data from the other.
Finally, although it is a critical enabler for military operations, interoperability must be recognized as just one of several technical attributes of any system of systems. Indeed, other attributes will sometimes be in competition with interoperability and with each other; an appropriate balance must be sought. For example, there are trade-offs between security and interoperability. Interoperability can promote an attacker's access to diverse systems, thus facilitating the rapid spread of attacks. Also, ad hoc work-arounds to overcome a lack of inherent interoperability can introduce many hard-to-manage security problems. Another trade-off is the potential for interoperability problems posed by the introduction of new security features into part of a larger system of systems. Thus, in thinking about overall system functionality or performance, security requirements such as confidentiality, authentication, non-repudiation, integrity, and system availability must be considered together with interoperability.