Introduction Though the prevalence and quality of telecommunica-tion networking has undergone leaps and bounds sincethe telephone was first invented in 1847, yet the adapta-tion of large-capacity networking in developed countriesremain rather limited and in certain fixed areas, which hasturned the majority of the developing countries to con-tinue searching for solutions through VPN and remotearea high-quality communications applications. TheVSAT technology that begun in the 90s not only servesto provide regional services through intangible wiringroutes but also provides comparable competitiveness infunctionality, service types, accessibility, transmissioncost, expansion cost and so forth when compared withtangible wiring routes.

1.Introduction of the VSAT technology VSAT,the acronym of very small aperture terminal, sig-nifies a ‘‘small-diameter ground terminal” in straightinterpretation, deriving from the fact that the wiring diam-eter of a VSAT system’s ground tends to be smaller, usu-ally between 0.3m and 2.4m. A new satellite communica-tions system developed in the mid 90s utilizing the mod-ern technology, VSAT systems come with characteris-tics of a dynamic flexibility, dependability, low cost, easyto use, and a direct linkup to the user through a localstation. Whereby a VSAT user terminal can link up di-rectly to a remote server through satellite channel to com-plete data transmission, document exchange or even re-mote processing to resolve the problem of ground sta-tion signal interruptions. In light of which, in remotespots where the ground networking-infrastructure maybe less than perfected, the quality of communicationswiring may be poor, or in the absence of a high-speedtransmission networking, the adaptation of the VSAT sys-tem would poise to improve the foresaid problems.

2.Characteristics of the VSAT system

A VSAT networking framework comprises of severalsmall VSAT substations and a main hub working togetherto constitute a wide-area networked (of a multi-stationconfiguration of smaller substation workload) satellitecommunications network. Compared with a grounds t a t i on commun ica t i ons ne twork , a VSATcommunications network offers the following ninecharacteristics:

(1)Its signals cover a far-flung area; (2)It is able to provide to all ground stations the identicalservice types and broadband service quality, includingerror bit rate, transmission delay, etc.; (3)Offering fine expandability with low expansion costand a relative short time for installing new communicationstations of smaller diameter antenna, and easy systemlaunching and maintenance; (4)Offering fine flexibility, where a multiple of servicescan be combined in a single network and provide variedservice types, with adjustable feature for bandwidthallocation and quality grade; (5)Offering fine communication capability of point topoint, one point to multiple points, multiple points tomultiple points, whereby the user can communicate withother users without routed through the ground station; (6)As a user designated communications network, it isnot confined by the telecommunications provider, hencewarranting an outstanding independent operability, andbesides fixed equipment, there are choices of mobileequipment; (7)Offering fine inter-working capability for users onvaried communications protocols can communicatethrough the same VSAT network using different groundstations; (8)Offering fine communications quality, with lowererror bit rate and shorter networking response timing; (9)A VSAT system offers intelligent functions, i.e.intelligent operations, interface, IT supportive operationsand frequency management) to allow man-less operationsto conserve operating manpower.

3.The VSAT system development is divided intothe following three phases (1) Initial phase: This phase pertains to that around1980, when C band is used as the primarily communicationchannel, and is limited to digital services of one-wayreception and low-speed transmission.

(2) Intermediary phase (first generation):Of equipmentdeveloped during 1983 and 1988, which cover not onlynewly developed multi address linkup but characterizedby a Ku band and satellite-configured networkingframework in digital transmission. (3) Near phase (second generation):Secondgeneration VSAT is now being transformed from a simpledigital transmission mode to an integrated digital/voice/graphic service orientation, together with a networkingcommunication framework, which covers the timeline ofroughly from 1988 to the mid 1990s. Since mid 90s, VSAT has begun broaching towardsthird generation function development, which ischaracterized by a stepped-up management and controlcapability, meaning using software to control a VSATsystem operations. At present, the VSAT systems are broaching towardsthe direction of standardized hardware and software,allowing VSAT equipment to provide a rudimentaryoperating platform function in essential networking, andthat the addition of module configured hardwareequipment and operating software, made to the userrequirements, can further enhance a VSAT systemnetworking exchange and transmission functions.

4.The VSAT system applications Besides designated broadband operations, a VSAT sat-ellite communications network also supports the existingoperational services, such as voice, digital, fax, LANlinkup, Audiovisual teleconferencing system, low-speedgraphic transmission, FR interface-based interactivegraphic prompting, television and digital music services;some of its tangible operational categories and typicalapplications are as charted below,

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5.The VSAT networking framework (1)Main hub The main hub serves as the central nerve of a VSATnetwork, and operates on large-scale antenna same asthe general ground stations with a diameter measuringapprox. 3.5m to 8m (on Ku band) or 7m to 13m (on Cband). When applied in digital services, a VSAT mainhub serves as the processing center and also thenetworking control center, where at the same time themain hub is equipped with a networking control center(NCC), which is responsible for monitoring, managing,controlling and maintaining various facilities. Whenapplied in voice services, a VSAT system’s control centercan be placed in the same station as the services centeror in a separate station. In addition, to facilitate equipmentmounting, dismounting and assembly, the main hub isusually in a modulated structured, and links up to varioussubstations using the high-speed regional networkconfiguration.

(2)VSAT substations A VSAT substation is comprised of three elements– the small diameter antenna, outdoor unit (ODU) andindoor unit (IDU). Under identical setting, i.e. identicalbandwidth, frequency projector, etc., a voice VSATnetwork’s substations serve to provide direct linkupbetween the substations, and whose antenna designwould ominously be larger than that of the digital SVATsubstations that only communicate with the main hub.

(3)Satellite attenuator First generation VSAT network operates on Cband attenuator, and second generation VSAT andonward are largely operating on the Ku band. As to theoperating bandwidth, it has not been tied to theoquipment but rather whether the satellite itself comeswith the resources of frequency conversion equipment.

6.VSAT’s LAN applications Given that the adaptation of a VSAT system in regionalnetworking (LAN) helps to enhance the dependabilitybetween networks, since mid 90s, the VSAT systems areable to support serially connected interfaces to a LAN/MAN network knot interfaces. Communications betweena VSAT network and LAN can either be in a direct modeor an intermediary mode. When communicating directlywith LAN using a VSAT system, there are three optionsof using a bridge device, router or streamliner, and variedlinkup methods would produce varied effects in VSATsystem communications protocols, bandwidth utilizationand flexibility. Some of the prevailing LAN protocolsinclude TCP/IP, SNA, DECnet, IPX and the like.

7.Concept for the Coast Guard Administration’sadapting the VSAT system A predominant poor quality of communications at theadministration’s remote areas, namely at offshore andcoastal islands, has stemmed from Chung HwaTelecommunications Company’s insufficient broadbandnetworking infrastructure for remote regions, such as theCoast Guard’s ADSL linkup. In search of resolving andimproving remote regions’ broadcast communicationsissue, the VSAT system emerges as an optimal solution.In the case of the Dong Sha and Nan Sha regions that fallunder the administration’s jurisdiction that are in dire needof improvement, a conceptual drawing is hereby presenteddepicting the adaptation of a VSAT system in the DongSha and Nan Sha regions as showed below,

Adopting the VSAT system for integrating voice, dataand video multimedia signals is not only a current trendbut best support the administration’s communicationneeds, as i t serves more than receiving andaccommodating signals of various defense units on theisland, and signals transmitted back to the Taiwan mainisland would allow Southern Regional Patrol bureau,General Coastal Patrol Agency, or even the Coast GuardAdministration to contact the superior units at the DefenseDepartment on islands that are manned by defense troopsthrough the administration’s external linkup circuits,offering the islands a comprehensive and multimediacommunication quality. It is highly anticipated that theVSAT system can be prompted as a shared regionalnetwork for all outpost personnel stationing at offshoreand coastal islands under various governmentdepartments that would poise to improve the currentphase’s poor communication problem. (The author is a specialist in communications and lo-gistics section at the General Coastal Patrol Agency ofthe Coast Guard Administration)