The use of direct-broadcast communication satellites and low-profile portable receive antennas is an effective means to provide high-bandwidth to mobile units. This type of system, with low cost receiving units, enables access to a wide range of information sources. Supported by the Defense Advanced Research Projects Agency (DARPA) under the Battlefield Awareness and Data Dissemination (BADD) program, a team was assembled to develop and demonstrate network protocols for the Global Broadcast Service (GBS), a system currently being acquired by the Air Force Space and Missile Systems Center (SMC). GBS will provide broadcast video, voice, and data from stateside and other information sources to user in a theater of operations.

We review early influences on the GBS network architecture and protocols, including work done for a Joint Warrior Interoperability Demonstration (JWID) and commercial direct-broadcast communication systems. We then discuss the design of the BADD GBS network architecture, which is intended to use open Internet technology that permits interoperation with existing and future systems. At the same time, the GBS network architecture exploits special capabilities of GBS, such as native multicast. We discuss also the technical challenges overcome, such as how to utilize effectively links that are unidirectional, how to implement connectionless Internet services over connection-oriented Asynchronous Transfer Mode (ATM) links, how to achieve high throughput with "long fat pipe" (high-latency, high-speed) links, and how to implement desirable services (such as World Wide Web browsing and periodically "pushed" data distribution) efficiently.

The core system has been implemented and includes standard Internet protocols adapted for unidirectional routing by means of modified routing protocols and a scheme for using reachback links called Virtual Internet Protocol with Reachback (VIPRE). The so-called Long Fat Pipe Transmission Control Protocol (LFN TCP) and the Transport for Reliable Multicast (TRM) protocol are used to support reliable, flow-controlled data exchange. Other services, such as Web access, are supported by caching schemes that place frequently requested information at sites in the theater of operations to promote low response times and reduce congestion on the satellite links. The system is operational and in use by military commands. Extensions to the core system, including improved network management, information assurance, and support for quality of service, are currently being designed and implemented.