SATELLITE/TERRESTRIAL INTERFACE

Technology in Europe

At the Europea n technology centers this panel visited, little interest and effort were evident for integrating advanced-satellite (broadband) and terrestrial fiber-optic networks, with some exceptions. The interests and efforts in satellite/terrestrial interface techn ology that were identified are described below.

Within organizations that are R&D leaders, such as ESA and the European Commission (EC), only nominal attention is given to this technology -- as is manifest from the following information and commen ts. Descriptions of ESA's current and future programs note that about 10 percent of ESTEC's budget is committed to communications satellite research, and that the Advanced Systems and Technology Program (ASTP) includes such components as integrated broad band communication network studies and opto-electronics and network protocol studies (part of Telematics). Yet, comments such as the following also were noted: "The PTTs have not been interested in satellites." "The relationship between satellite and terrestrial systems [understood to mean networks] must be redefined." "Lack of communications infrastructure in such areas as Eastern Europe and remote locations such as Iceland represents a situation for which satellites are a ke y resource."

Within the EC, about $6 billion will be directed over the next five years to R&D in communications and information technology. However, there is very strong emphasis on terrestrial communications; therefore only about 1 percent of this budget will be directed to satellite communications R&D. But, there is no interest in satellite/terrestrial interface technology because of the perception that fiber-optic cable is becoming the dominant transmission medium for broadband netwo rks, including networks for most international services.

EUTELSAT, a consortium originally formed to provide satellite telephony throughout Europe, has several R&D projects that include study/development of satellite/terrestrial interface technolo gy. These include the Research in Advanced Communications Experiment/Europe (RACE) project, the Users, Network Operators, and Manufacturers (UNOM) project, and the Catalyst project. Specific detailed information about the satellite/terrestrial interface technology aspects of these projects was not explored during the visits and has not been available during the preparation of this report. Two factors that likely will continue to stimulate interest at EUTELSAT in satellite/terrestrial interface technolo gy R & D are (1) the rapid growth in membership that is occurring as Eastern European countries join, which likely will increase the demand for public telephone and data services in those areas, and (2) the rapid growth in the types of services being provided (currently, television distribution is the major service).

In visits to companies that are doing much of the R&D work planned and funded by ESA, it was found that 20/30 GHz transponders (payloads) are being built (by Alenia Spazio in Ital y) and experiments are being planned and conducted (by Telespazio in Italy) to evaluate performance provided by using hybrid (satellite/terrestrial) networks on ITALSAT F1, F2, and F3 (proposed). The ITALSAT F1 satellite, launched in January 1991, is the space segment of a multibeam, digital system that operates in the 30/20 GHz band and provides on-board switching using a baseband matrix switch. According to one of the panel briefings, ITALSAT experiments include an experiment that "offers circuit s to the terrestrial network" on a semi-permanent as well as demand basis, providing full duplex connections between pairs of terrestrial exchanges. Details were not discussed, and efforts to obtain additional information after the visit have not be en successful. The hosts at Alenia Spazio, however, did not express optimism about the long-term commercial opportunities that will follow the present and planned R&D work and experiments.

It also was noted in the visit to DTL that Germany plans to use existing satellite resources to provide public switched telephone network (PSTN) services to areas of former East Germany where terrestrial network infrastructure is lacking, but details of the technology that is planned to be used are not known. It seems likely that new technology development is neither required nor planned.

Another aspect of the state of satellite/terrestrial network interface technology in Europe is that the development of the interface technology tends to be fragmented in two ways. First, the technology development pertaining to the satellite network is done by companies doing other space communications technology, for example inter-satellite link (ISL) communications technology, and interface technology development perta ining to the terrestrial network is done by companies doing other terrestrial communications technology. And, to date, that network technology development has been in an environment of considerable regulation imposed on the PTTs concerning the provision of telecommunication services. However, interface technology development in Europe is not so different from the way this technology development is done in the United States, despite the fact that telecommunication services are considerably less regulated in the United States, and therefore are able to be more innovative.

A second factor leading to fragmented technology development is that, generally speaking, European companies that do space technology development are members of ESA. Technology deve lopment work under the direction of ESA is funded entirely by members' contributions (essentially voluntary) to the Agency. It is, however, required that ESA contracts be awarded to companies in the membership countries in proportion to each member's con tribution. This constraint, coupled with the natural distribution of technological expertise, may bias the emphasis placed on particular technology development efforts (contracts). An example is Germany, a country currently experiencing economic stress because of political unification. This economic stress has forced Germany to stop making contributions to ESA, yet it is a country with extensive space technology expertise. Similar constraints are not so evident, at least, in the United States.

Te chnology in Japan

Japanese national government agencies and technology centers, in planning for broadband networks of the future, raise questions concerning the respective roles for terrestrial fiber-optic cables and advanced satellite networks, an d are cautious in planning for the integration of these networks. Technology and policy leaders, noting that some trunking and restoration of services (for the PSTN) using satellite networks do seem possible in the future, stated that they want to " keep their options open." Such thoughts were expressed, for example, during the visit at the MPT Space Communications Policy Bureau, one Japanese government agency that defines and funds R&D programs in space communications.

Looking at curr ent technology applications, the panel learned that Nippon Telephone and Telegraph (NTT) Corporation (the dominant entity providing domestic telecommunication services) has developed an operational network capability known as DYANET-II (DYnamic channel As signing and routing satellite-aided digital NETwork). DYANET-II uses the CS-3 satellites to provide "common alternative routing" for PSTN trunks and subscriber circuits to connect remote Integrated Services Digital Network (ISDN) users into the terrestrial service access points. The configuration of the network is shown in Figure 4.2. DYANET-II has required the development of new network control and switching technology.

This common alternative routing capability, th at connects 62 switching centers throughout Japan, provides more than 6,000 equivalent voice circuits for emergency back-up to the terrestrial network and transmission capacity for traffic overload conditions between major regional centers. The satellite -based subscriber connections for remote ISDN users are limited at this time to a small number of earth terminals where basic- and primary-rate interfaces are available.

Within Japan's communication satellite technology development and application c enters, some thought has been given to the need for new satellite/terrestrial interface requirements and capabilities. However, conclusions that establish needs or requirements, and become the basis for new interface technology development work, are quit e tentative. For example, NTT expresses its goal as "to facilitate communications in the new advanced information-age society." And NTT officials acknowledge that sophisticated, basic technology, including satellite and fiber-optical technolog y for high-speed, long-haul, bulk information transport will be required. Their work in the development of high-speed networks, specifically broadband-ISDN (B-ISDN), is strong evidence of the pursuit of that goal. Their work on satellite communications, however, is only about one-tenth the size of their effort on (terrestrial) high-speed networks.

Similarly, the Kokusai Denshin Denwa (KDD) Company, Ltd. (which provides international telecommunication services) is developing B-ISDN technology at data rates greater than 150 Mbits/sec for applications using fiber-optic cables (and fiber-optic communications technology at data rates up to 10 Gbits/sec). But their attitude toward the use of satellites for high-data-rate telecommunications is somewhat of a conundrum. They recognize the need for international B-ISDN services, but consider satellites to have no advantage and, therefore, are devoting no effort to developing satellite-based B-ISDN. In contrast, they recognize that satellites have some adva ntages for supercomputing networks, but see no need, as Japan's international telecommunication services provider, for providing such services. Today, a principal thrust within KDD is the development of new ISDN services. Less than one-fourth of the wor k at the KDD R&D Labs (about 30 researchers) is directed to satellite communications. Several years ago about one-half of their work was devoted to satellite communications.


Figure 4.2. Network Configuration of DYANET-II

As noted earlier for Europe, in Japan the development of satellite interface technology also tends to be fragmented. Technology development that is being done by the organizations visited is directed str ongly to space communications that utilize ISLs. The technology that applies to interface between satellites and the terrestrial fiber-optic network often is being developed by other organizations without clear objectives for maximizing opportunities for integrated networks.

Technology Status and Development Summary

The technology for interfacing satellite and terrestrial networks is in many ways more of an applications technology than it is basic-science technology. Consequently, the develo pment of interface technology is more closely associated with commercialization than with development of communications satellite technology. Commercialization is influenced by perceived market opportunities as well as projected requirements by both user s and providers. Development required for commercialization may be promoted and conducted by different organizations than those doing the basic-science technology development. Commercialization also is often dependent on national and international polic ies pertaining to telecommunication services.

This thought is significant in another way. That is, the dominant interests of this panel were the status and development of basic technologies pertaining to satellite communications. Therefore, the pa nel tended to visit centers where policies and funding for the basic technologies are established and technology centers where development work is being done. Did the panel, then, fail to become aware of interface technology development that is being don e? Perhaps, but it is believed the panel's information is not significantly lacking; rather, that planning for integrated networks (which, logically, becomes the basis for developing interface technology) is seriously lacking world-wide. Generally speak ing, there was limited interest in and very limited effort devoted to satellite/terrestrial network interface technology in either Japan or Europe. The panel believes the situation is no better in the United States.

Illustrations of policy, planning, and interface technology, both applied and being developed, are provided by the following examples. These examples include very general conclusions about the status of satellite/terrestrial advanced network interface technology in the three major region s of the world. Throughout the world, international digital services, including voice, data, and video, are provided both by satellite circuits and fiber-optic cables, with satellite circuits providing full back-up for trans-oceanic cables. Though not i nvestigated as part of this study, the interface technology implicit in providing these services is significant and well-developed.

U.S. carriers avoid the use of satellite links for voice circuits in the PSTN, though distribution of video programming and other digital services using satellite circuits are extensive and commonplace. Satellite circuits also are common in private networks for voice, data, and video traffic. The status of advanced satellite/terrestrial interface technology development in the United States is characterized as experimental technology -- the technology embodied in ACTS. That technology includes interface equipment to provide twenty-eight 64 kbits/sec channels that may be interconnected with the terrestrial network , accommodation for ISDN protocol conversion and PBX equipment that may be added to the ACTS T1 VSATs, and capabilities for high-data-rate (HDR) services (rates up to 622 Mbits/sec) using the HDR terminals.

In Europe, satellite circuits are integrated with the terrestrial network for providing public switched services, including voice. For example, the ITALSAT F1 provides 12,000 equivalent voice channels integrated with the public network in Italy. In Germany, the DFS satellites provide domestic pub lic telecommunications that include telephony, data, and television distribution. Such capabilities have been particularly useful in establishing and expanding services in the area formerly known as East Germany. The status of advanced satellite/terrest rial interface technology development in Europe is characterized as pre-operational technology expected to migrate to operationaltechnology -- the technology typified by ITALSAT. Interface technology that may be experimental on OLYMPUS or expanded on subsequent ITALSATs was not identified or discussed during the panel's visits.

Satellite circuits also are integrated with the terrestrial network for providing public switched services in Japan. These capabilities include alternate routi ng for voice and subscriber circuits for remote ISDN users. The status of advanced satellite/terrestrial interface technology development in Japan is also characterized as pre-operationaltechnology expected to migrate to operational technol ogy -- the technology typified in DYANET. Interface technology that may be experimental on ETS-VI was not identified or discussed during the visits.

These conclusions seem valid despite the fact that satellite telecommunication applications in Europe , Japan, and the United States are "driven" by different policies, factors, and objectives. Table 4.2 contrasts and highlights some of these differences.

Table 4.2
Factors Influencing the Development of Satellite Telecommunication (T/C)
Applications in the United States and Europe and Japan


Published: July 1993; JTE C/WTEC Hyper-Librarian