Service offerings and interfaces for the ACTS network of earth stations

Abstract

SUMMARYThe Advanced Communications Technology Satellite (ACTS) Is capable of two modes of communication. Mode 1 1s a mesh network of Earth stations using baseband-switched, time-division multiple-access (BBS-TDMA) and hopping beams. Mode 2 1s a mesh network, using satellite-switched, time-division multipleaccess (SS-TDMA) and fixed (or hopping) beams.The purposes of this paper 1s to present the functional requirements and the design of the ACTS Mode 1 Earth station terrestrial Interface. Included o, among the requirements are that (1) the Interface support standard telecommunl-°° cations service offerings (I.e., voice, video and data at rates ranging from°? 9.6 kbps to 44 Mbps); (2) the Interface support the unique design characterism tics of the ACTS communications system (e.g., the real time demand assignment of satellite capacity); and (3) the Interface support test hardware capable of validating ACTS communications processes. The resulting Interface design makes use of an appropriate combination of Tl or T3 multiplexers and a small central office (maximum capacity 56 subscriber lines per unit). SERVICE OFFERINGSThe NASA ACTS Project Office at NASA Lewis Research Center, Cleveland, Ohio, will acquire a number of Earth stations to operate as a Mode 1 network. This network of Earth stations will support two ACTS program objectives: to verify the technical performance of ACTS Mode 1 operation In geosynchronous orbit and to demonstrate the types and quality of services that can be provided by an ACTS Mode 1 communications system. The terrestrial Interface design 1s a critical element in assuring that these network Earth stations will meet the objectives. The following 1s a discussion of the applicable terrestrial interface design requirements, the resulting interface specifications, and the associated terrestrial input/output hardware. A functional block diagram of a network Earth station ( fig. 1). TERRESTRIAL INTERFACE DESIGN REQUIREMENTS ACTS Mode 1 Telecommunications ServicesTo enhance the likelihood of experimenter Involvement with ACTS, the terrestrial Interface must be easily Integrated Into existing communications plants. This means that the Earth station Interface must be adaptable to the experimenter communications hardware and protocols, rather than vice versa. Therefore, three types of communications plants will be supported by the ACTS Mode 1 network and the network Earth station terrestrial interfaces: PBX's, key systems, and multiple subscriber lines.Associated with each plant type are a variety of standard telecommunications services and potential experiments. Within practical limits, the Interface must support those services and experiments. Three categories of service will be offered with each of the above plant types (table 1). (This classification by data rate Is done to simplify discussion only.) The first category of services 1s equivalent to today's terrestrial service offerings, as typified by analog voice and data rates of ^56 kbit/sec. The second category expands these services to Includ...