U.S. Army Information Systems Engineering Command
Fort Huachuca, Arizona 85613-5300

Automated Information Systems

Design Guidance

Commercial Satellite Transmission

Working (August 1998)

Table of Contents


        1.1 Purpose
        1.2 Background
        1.3 Goal
        1.4 Scope


        2.1 Department of Defense Standards

        2.1.1 Technical Architecture Framework for Information Management (TAFIM)
        2.1.2 Joint Technical Architecture (JTA)
        2.1.3 Defense Information Infrastructure (DII) Master Plan
        2.1.4 DII Common Operating Environment (COE)
        2.1.5 DoD Directives (DoDD) and DoD Instructions (DoDI)
        2.1.6 Chairman of the Joint Chiefs of Staff Instructions (CJCSI)
        2.1.7 Defense Information Systems Agency (DISA)
        2.1.8 Defense Information System Network (DISN)

        2.2 Industry Standards

        2.2.1 Architecture
        2.2.2 Earth Terminals


        3.1 Office Director of Information Systems for C4 (ODISC4)
        3.2 Joint Technical Architecture-Army (JTA-Army)
        3.3 U.S. Army Communications-Electronics Command (USACECOM)
        3.4 U.S. Army Information Systems Engineering Command (USAISEC)


        4.1 Commercial Satellite (COMSAT) Communications

        4.1.1 Minimum Essential Requirements
        4.1.2 Architecture
        4.1.3 Migration Strategy
        4.1.4 Legacy Systems
        4.1.5 System Design Guidance
        4.1.6 Procurement Source Hardware and Software
        4.1.7 Areas to be Coordinated and Developed by the System Engineer (SE)
        4.1.8 Satellite Link Budget
        4.1.9 Look Angle
        4.1.10 Satellite Footprint

        4.2 Satellite Service

        4.2.1 Fixed Satellite Service (FSS) in Europe
        4.2.2 Fixed Satellite Service (FSS) in Japan
        4.2.3 Fixed Satellite Service (FSS) in Russia
        4.2.4 Mobile Satellite Services (MSS)

        4.3 Commercial Satellite Communications Initiative (CSCI)

        4.4 Global Broadcast System (GBS)

        4.5 Interference Reduction Group (IRG) Standard Access

        4.6 Transponder Rates

        4.7 Teleports

        4.8 Personal Communications System

        4.8.1 Transport Mechanisms: TDMA & CDMA
        4.8.2 PCS Technologies: DCS-1900 (GSM), IS-136 and Qualcom's CDMA
        4.8.3 IRIDIUM System

        4.9 Medium Earth Orbit (MEO) Satellites

        4.10 Low Earth Orbit (LEO) Satellites

        4.11 Modern Satellite Networks

        4.11.1 INMARSAT B High Data Rate Gateway Switch
        4.11.2 Intelligent Networks
        4.11.3 Asynchronous Transfer Mode (ATM) over Satellite
        4.11.4 Advanced Very Small Aperture Terminal (VSAT)
        4.11.5 Second Generation Time Division Multiple Access (TDMA)

        4.12 Research Fields

        4.12.1 Wide Area Communications Server
        4.12.2 Data Communications
        4.12.3 ACTS Frame Relay
        4.12.4 ISDN
        4.12.5 ISDN, SDH and ATM via INTELSAT
        4.12.6 Mobile Satellite/Terrestrial Interworking

        4.13 Transmission Security

        4.13.1 The Multilevel Information System Security Initiative (MISSI)
        4.13.2 Bulk Encryption System


1.1 Purpose

This commercial satellite transmission Design Guide provides technical guidance to integrate commercial satellite transmission support in the overall design of United States (U.S.) Army Automated Information Systems (AIS). This guidance furnishes the engineer and program manager information leading to development of more detailed System Design Plans (SDP) for specific applications. This design guide will be reviewed periodically and kept current with changes in established architectures and significant advances in the state-of-the-art for commercial satellite transmission systems. The U.S. Army Information Systems Engineering Command (USAISEC) point of contact (POC) for commercial satellite transmission systems is Mr. Jim Hinkle, email: [email protected].

1.2 Background

The Department of Defense (DoD) promulgated new policy guidance for the use of commercial satellite (COMSAT) communications. This policy was an outgrowth, in part, of Congress mandated studies.  The CSCI studies demonstrated the applicability of COMSAT to a variety of command, control, communications, and intelligence (C3I) missions. To ensure maximum savings, all acquisition of COMSAT services will be consistent with the approved Defense Information Services Network (DISN) acquisition strategy and will be acquired through the Defense Commercial Communications Office (DCCO) of the Defense Information Systems Agency (DISA).   Along with CSCI, this guide reviews ATM via Satellite, Security issues for COMSAT, Global Broadcasting System, LEO/MEO systems, advanced communications technology satellites (ACTS), and other subjects important for the commercial satellite transmission systems design engineer.

1.3 Goal

The goal of this document is to provide, to Army AIS designers, information on policy guidance, standards, design constraints, and current practice applicable to COMSAT transmission systems.

1.4 Scope

This document contains pertinent information from DoD and Army Command, Control, Communications, Computers, and Intelligence (C4I) architectural and technical standards, including the:

These standards provide the programatic guidance for systems and COMSAT transmission. Transmission architects must understand the total system requirements to ensure proper performance and interoperability. The Installation Information Transfer System (IITS) Design Guidance and IITS Policy and Technical Application documents provide detailed lists and appropriate applicability of those standards that apply to new installations and to major upgrades. An evolving list of standards and references, including brief abstracts of many of the standards, is available from the DISA Joint Interoperability Engineering Organization (JIEO) Center for Standards - Information Technology Standards Document library.


The following chapter provides a general reference for applicable DoD and industry standards, architecture, and systems that define the context for Automated Information Systems COMSAT transmission systems. A short summary paragraph is provided for each with the appropriate hot link uniform resource locator (URL) provided for additional detail, if available. This chapter is primarily provided for reference and definition purposes.

2.1 Department of Defense Standards

The DoD Standards Reform began in June 1994 when the Secretary of Defense issued his memorandum entitled "Specifications and Standards - A New Way of Doing Business." This memorandum directs that performance-based specifications and standards or nationally-recognized private sector standards be used in future acquisitions. The intent of this initiative is to eliminate non-value added requirements, and thus reduce the cost of weapon systems and material, remove impediments to getting commercial state-of-the-art technology into our weapon systems, and integrate the commercial and military industrial bases to the greatest extent possible. The JTA implements standards reform by selecting the minimum standards necessary to achieve joint interoperability. The JTA mandates commercial standards and practices to the maximum extent possible.

2.1.1 Technical Architecture Framework for Information Management (TAFIM)

The DoD JTA draws on the TAFIM, which provides general guidance, and documents the processes and framework for defining the JTA and other technical architectures. The TAFIM applies to many DoD mission/domain areas and lists all adopted information technology standards that promote interoperability, portability, and scalability.

2.1.2 Joint Technical Architecture (JTA)

The JTA is the baseline for DoD systems design guidance. It identifies a common set of mandatory information technology standards and guidelines to be used in all new and upgraded systems across DoD. The scope of the JTA is focused on command, control, and intelligence (C2I) systems (to include sustaining base, combat support information, and office automation systems), the communication computers that directly support the C4I, and the interfaces of those systems with other key assets (e.g. weapon systems, sensors, models, and simulations) to support critical joint warfighter interoperability.

2.1.3 Defense Information Infrastructure (DII) Master Plan

The DII Master plan is a tool to manage the evolution of the DII. The purposes of the DII Master Plan are to:

  1. Establish the common vision of the DII for the DoD to ensure unity of effort.
  2. Provide information about the DII and DII initiatives for use by customers, planners, program managers, action officers, and policy makers in developing the elements of the DII.
  3. Define the roles, responsibilities, and relationships of all DII participants.
  4. Identify the elements that comprise the DII.
  5. Provide a road map for the migration and implementation of DII elements.
  6. Identify the relationships and interdependencies of DII initiatives.
  7. Assist in integrated planning and implementation of DII efforts across DoD to ensure that the right resources are programmed to do the right things at the right time by the right organizations.
  8. Establish standard definitions and a lexicon glossary of DII terminology.
  9. Describe initiatives that eliminate the shortfalls in the current information infrastructure.

2.1.4 DII Common Operating Environment (COE)

The DII COE details the technical and functional requirements for a common operating environment for information support to the warfighter. It identifies classes of functions common to all or most application components.

The development of the DII COE stems from the Global Command and Control System (GCCS) COE effort and is perhaps the most significant and useful technical by-product of the GCCS development effort. As an outgrowth of this effort the Services have agreed to migrate their command and control (C2) systems to the DII COE.

2.1.5 DoD Directives (DoDD) and DoD Instructions (DoDI)

The following DODD promulgates policy for compatibility, interoperability, and integrity of C3I systems used in the DoD.

DoDD 4630.5 "Compatibility, Interoperability, and Integration of Command, Control, Communications, and Intelligence (C3I) Systems."

The following DoDI implements the policy in DoDD 4630.5, assigns responsibilities and prescribes procedures to achieve compatibility and interoperability of a consolidated, DoD-wide, global infrastructure.

DoDI 4630.8 "Procedures for Compatibility, Interoperability, and Integration of Command, Control, Communications and Intelligence (C3I) systems."

2.1.6 Chairman of the Joint Chiefs of Staff Instructions (CJCSI)

The following CJCSI implements the policy established in DoDD 4630.5 and DoDI 4630.8, supports C4I for the warrior (C4IFTW) initiative, makes the Military Communications-Electronics Board (MCEB) the focal point for enforcement of the policy.

CJCSI 6212.01A, "Compatibility, Interoperability, and Integration of Command, Control, Communications, Computers, and Intelligence Systems"

2.1.7 Defense Information Systems Agency (DISA)

The DISA core mission includes DISN, GCCS, and the Defense Message System (DMS). The mission is "to plan, engineer, develop, test, manage programs, acquire, implement, operate, and maintain information systems for C4I and mission support under all conditions of peace and war". DISA is the DoD agency responsible for information technology. The area of concern for this guide is the DISN portion of DISA's mission.

2.1.8 Defense Information System Network (DISN)

The DISN is the DoD's consolidated worldwide, enterprise-level telecommunications infrastructure that provides the end-to-end information transfer network for supporting military operations, national defense C3I requirements, and corporate defense requirements. DISN is the communications transport piece of the DII, which is a widely distributed, user-driven infrastructure into which the warrior can gain access from any location for all required information. The DISN is structured to satisfy requirements that are evolving in response to changing military strategy, changing threat conditions, and advances in information and communications technology. The DISN infrastructure encompasses a Continental United States (CONUS) sustaining base segment, segments outside CONUS (OCONUS) in the European and Pacific theaters, a space segment, and a deployable capability.

The DISN Network will:


Table 1 shows the relationship between the different agencies and their area of responsibilities.

Table 1. Agency Responsibilities.

TAFIM General guidance describing the architectural development process.
General Guidance
JTA Identifies standards/specifications to define performance criteria and interoperability criteria used when developing system designs.
Concept DII Master Plan - Identifies major switching, routing, and communication facility elements along with the associated Technology (circuit switch, Asynchronous Transfer Mode (ATM), Transmission Control Protocol/Internet Protocol (TCP/IP), SATCOM, fiber cable) and identifies associated implementation program.
Architecture DII DII COE - User information services, functions, and allocation of functions.
DII DISN - User telecommunication services, strategic/tactical connectivity, switching and routing architecture, communication facilities, network management.
Implementation USAISEC System development plan, site surveys, engineering installation plans, test and acceptance.

2.2 Industry Standards

2.2.1  Architecture

A detailed listing of information transfer mandated standards and Internet links to these standards is identified in Appendix B of the JTA. These standards are required for interoperability between and among systems, supporting access for data, facsimile, video, imagery, and multimedia systems. Also identified are the standards for internetworking between different subnetworks and transmission media standards for Synchronous Optical Network (SONET) and radio links. These standards promote seamless communications information transfer interoperability for DoD systems. 

2.2.2  Earth Terminals

Commercial satellite earth terminal standards are derived from commercial sources.   Reference the Intelsat Standards to ensure earth terminal compliance.  Other satellite transponder service providers (for example:  INMARSAT, and EUTELSAT) also establish their own earth terminal requirements to ensure that the earth segment will not damage the satellite or interfer with other users.  


This chapter provides a general reference for applicable DoD and industry standards, architectures, and systems that define the context for AIS COMSAT Transmission Systems. A short summary paragraph is provided for each with the appropriate hot link URL provided for additional detail if available. This chapter is primarily provided for reference and definition purposes.

3.1 Office of the Director of Information Systems for C4

The Office of the Director of Information Systems for Command, Control, Communications, and Computers (ODISC4) is the Army's Chief Information Officer, has Army responsibility for the Information Mission Area that supports total Army management and command and control requirements, and is responsible for the information management policy of the Army. The ODISC4 was directed to develop and implement the JTA-Army as detailed in AR25-1 Army Information Management.

3.2 Joint Technical Architecture-Army (JTA-Army)

The JTA-Army is the baseline for Army systems design guidance. It simplifies the DoD TAFIM in some ways by condensing the guidance, which is stated within the TAFIM in broad terms to encompass the entire DoD as an enterprise system, to Army-specific requirements. The JTA-Army defines a technical architecture as a minimal set of rules governing the arrangement, interaction, and interdependence of the parts or elements that together may be used to form an information system. Its purpose is to ensure that Army system development (and the migration of existing information systems) satisfies a specified set of requirements that lead to interoperability. The JTA-Army is compared with a building code. That is, it does not tell the engineer what to build or how to build; instead it delineates the standards that will have to be met to pass inspection before the system that is built can be used. Also, like building codes, the JTA-Army is a constantly evolving set of guidelines. As technologies and standards change, so will the JTA-Army.

The JTA-Army takes advantage of commercial investment in information technologies. It will not remain static but will evolve through participation with DoD, industry, and international standards organizations in order to identify trends and standards. The sections of the JTA-Army that most apply to long-haul transmission systems are primarily the communication transport standards and architecture.

3.3 U.S. Army Communications-Electronics Command (USACECOM)

USACECOM provides the architectural framework and systems engineering to ensure joint interoperability and horizontal technology integration across the battlespace. USACECOM executes its mission throughout the lifecycle of warfighting systems and platforms through an integrated process of technology generation and application, acquisition excellence and logistics power projection.

For Army sites affected by these projects, the USACECOM, USAISEC, and United States Army Signal Command (USASC) have different responsibilities in operating, engineering, designing, and implementation of these systems. This design guide identifies the available engineering, implementation, or test tools, handbooks, textbooks, government or industry technology documentation typically used in the engineering process for applicable USAISAEC responsibilities in commercial satellite transmission systems or projects. Table 2 shows a list of resources and references that are used in the SDP (System Design Plan).

Table 2. Information Sources for USAISEC SDP

Information Resources & Tools System Design Plan Reference
Master plan
Project authority.
JTA Mission Requirements.
Technical requirements, services, etc.
DII COE/DISN System concept - major elements and allocation.
USAISEC SDP System architecture, selection of
equipment. Equipment and DoD
standards, equipment standards,
system performance standards.
Demonstration and interface standards.
System installation plans.
System test plans.

3.4 U.S. Army Information Systems Engineering Command (USAISEC)

USAISEC has been assigned the lead operational element within USACECOM for implementing the procedures for and ensuring that all AMC engineered products adhere to architectural standards and are synchronized, integrated, and interoperable. This responsibility includes the development and maintenance of USAISEC Technical Guides and associated checklists that serve as architectural standards. These guides are based, in part, upon the policies, standards, and guidance promulgated by the various levels of DoD organizations discussed above. USAISEC will provide overall project and system engineering for the entire project. USAISEC will also conduct formal quality assurance (QA) and testing on a site, link, or system basis.


The following chapter identifies and explains the available engineering implementation, testing tools, programs, handbooks, government or industrial documentation typically used in the engineering process for applicable USAISC responsibilities in COMSAT projects and systems. As the use of COMSAT increases throughout the DoD, basic interoperability among Fixed Satellite Service (FSS) terminals will be established and maintained through the use of appropriate standards, in a manner consistent with advancing commercial technology. To the maximum extent practical, all new military transportable FSS Earth Terminals (ET) will be acquired with the ability to access the commercial C and KU frequency bands.

In many cases, DISA should be contacted to acquire commercial satellite service or direct the Design Engineer to the appropriate Commercial Agency.

4.1 Commercial Satellite (COMSAT) Communications

COMSAT Communications are used to support DoD’s Military Satellite Communications (MILSATCOM) capabilities where jamming protection is not required. This Commercial Satellite Transmission Design Guide provides guidance, engineering, and specialized information for the design and use of commercial satellites.

The three commonly used commercial satellite frequency bands are the C, KU and Ka Bands. C and KU Bands are the most common frequency spectrums used by today's commercial satellites. To help understand the relationship between antenna diameter and transmission frequency, it is important to note that there is an inverse relationship between frequency and wavelength. When frequency increases, wavelength decreases. As wavelength increases, larger antennas are necessary to gather the signal.

Compatibility of satellites with terrestrial networks has centered around three characteristics of satellite communications: delay, limited bandwidth, and noise. Noise will become less of a problem in future systems because of improvements in error correction coding. The limited bandwidth available to satellites makes it important to make efficient use of the link. Delay can cause problems with systems that are not set up to tolerate latency. The propagation time for a signal to travel up to a geosynchronous satellite and back down to earth is around a quarter of a second. This means a half second will elapse before a return message is received by a sender. Some protocols designed for terrestrial networks will time out before this under the assumption that such a time delay indicates congestion of the network.

4.1.1 Minimum Essential Requirements

The power transmitted from an earth station to the satellite to another earth station is a critical link which will be carefully designed in order for the link to work. Appendix 4 of the International Telecommunications Union (ITU) radio regulations details advance publication information to be furnished for a satellite network. This information reflects the actual spacecraft and the energy patterns of the individual transponders. Much of the information in the data fields is highly technical and will be supplied by an applications program through which the analyst will establish desired coverage area, orbital locations, etc. This program must generate coverage areas which reflect both the power source and the antenna sidelobe for each beam generated by the spacecraft.

The received microwave power involved in satellite links is typically very small (of the order of a few 100 picowatts). This means that specially designed earth stations that keep the carrier to noise (C/N) ratio to a minimum are used to transmit/receive satellite communications. The front end receiver is the most crucial part of the transceiver and is a major factor in the overall cost of the satellite Earth Station (ES). It typically employs a large antenna (Gain of a parabolic antenna is proportional to the square of its diameter) and a highly linear, low noise amplifier (LNA).

Satellite links can operate in different frequency bands and use separate carrier frequencies for the up-link and down-link. Table 3 shows the most common frequency bands. The use of C Bands was most common in 1st generation satellite systems. However, this band is already crowded as terrestrial microwave links also use these frequencies. The current trend is towards the higher frequencies of Ku and Ka Bands. Attenuation due to rain is a major problem in both of these bands. Also, microwave equipment for these frequencies is still expensive, especially in the Ka Band.

Table 3. Frequency spectrum allocation for common commercial SATCOM bands

C 3.7-4.2 5.925-6.425 Interference with ground links.
Ku 11.7-12.2 14.0-14.5 Attenuation due to rain.
Ka 17.7-21.7 27.5-30.5 High equipment cost.
L/S 1.610-1.625 2.483-2.500 Interference with ISM band.

Modern satellites are often equipped with multiple transponders. The area of the earth's surface covered by a satellite's transmission beam is referred to as the "footprint" (see Figure 1) of the satellite transponders. The uplink is a highly directional, point-to-point link using a high gain dish antenna at the ground station. The down link can have a large footprint providing coverage for a substantial area or a "spot beam" can be used to focus high power on a small region thus requiring cheaper and smaller ground stations. Moreover, some satellites can dynamically redirect their beams and thus change their coverage area.

Figure 1. Typical Satellite Footprint

4.1.2 Architecture

Satellite communication is a major element of the transmission and switching segment of the DISN architecture. COMSAT will support global-wide area networks of fixed and mobile terminals. The DISN architecture utilizes Broadband Integrated Services Digital Network (B-ISDN) as the predominant technology for the fixed environment and Asynchronous Transfer Mode (ATM) in the deployed environment. Satellite Constellations

Satellites can be positioned in orbits with different heights and shapes (circular or elliptical). Based on the orbital radius, all satellites fall into one of the following three categories.

The orbital radius of the satellite greatly affects its capabilities and design. Table 4 summarizes the features of different types of satellite constellations.

Table 4. Features of different satellite constellations.

Description Low Earth Orbit Medium Earth Orbit Geostationary Earth Orbit
Height 500-1000 miles 6000-12000 miles 22,282 miles
Time in LOS 15 min 2-4 hrs 24 hrs
Merits Lower launch costs. Short round trip signal delay. Small path loss. Moderate launch cost. Small round trip delays. Covers as much as 42.2% of the earth's surface. Ease of tracking.  No problems due to doppler.
Demerits Shorter life, 5-8 years.  Encounters radiation belts. Larger delays. Greater path loss than LEO's. Very large round trip delays. Expensive Earth Stations due to weak signals.

Satellites are also classified in terms of their payload. Satellites that weigh in the range of 800-1000 kilograms (kg) fall in the "Small" class, whereas the heavier class is referred to as "Big" satellites. GEO satellites are typically "Big" satellites, whereas LEO satellites can fall in either class. Media Access Control (MAC) Protocols for Satellite Links

Satellite channels have some unique characteristics that require special consideration at the DLC (Data Link Control) layer of the open system interconnect (OSI) model. The satellite links are often referred to as Long Fat Pipes; they represent paths with high bandwidth-delay product. Moreover, since they typically provide a broadcast channel, media sharing methods are needed at the MAC sublayer of the DLC. The traditional Carrier Sense Multiple Access/Collision Detection (CSMA/CD) schemes typically used in local area networks (LAN) cannot be used with satellite channels since it is not possible for earth stations to do carrier sense on the up-link due to the point-to-point nature of the link. A carrier sense at the down-link informs the earth stations about potential collisions that may have occurred 270 milliseconds (ms) ago (for GEO). Such delays are not practical for implementing CSMA/CD protocols.

Most satellite MAC schemes usually assign dedicated channels in time and or frequency for each user. This is because the delay associated in detecting and resolving multiple collisions on a satellite link is usually unacceptable for most applications. Typical MAC schemes are briefly discussed below.

ALOHA: Pure ALOHA allows all competing stations to transmit anytime. It has a very low efficiency of 18%. S-ALOHA (Slotted ALOHA) using the satellite broadcasts to synchronize the ground station transmissions to the start of a slot time, can improve the efficiency to around 36%. If the number of ground stations is fixed and small, it may be considered as an option.

FDMA: (Frequency Division Multiple Access) This is the oldest and still one of the most common methods for channel allocation. In this scheme the available satellite channel bandwidth is broken into frequency bands for different earth stations. This means that guard bands are needed to provide separation between the bands. Also the earth stations must be carefully power controlled to prevent the microwave power from spilling into the bands for the other channels.

TDMA: (Time Division Multiple Access) In this method, channels are time multiplexed in a sequential fashion. Each earth station gets to transmit in a fixed time slot only. More than one time slot can be assigned to stations with more bandwidth requirements. This method requires time synchronization between the ES which is generated by one of the ES and broadcast via satellite.

CDMA: (Code Division Multiple Access) This scheme uses a hybrid of time/frequency multiplexing and is a form of spread spectrum modulation. It provides a decentralized way of providing separate channels without timing synchronization. It is a relatively new scheme but is expected to be more common in future satellites.

The ability to use on board processing and multiple spot beams will enable future satellites to reuse the frequencies many times more than today's systems. In general, channel allocation may be static or dynamic, with the latter becoming increasingly popular. Demand Assigned Multiple Access (DAMA) systems allow the number of channels at any time to be less than the number of potential users. Satellite connections are established and dropped only when traffic demands them. Very Small Aperture Terminal (VSAT) Networks

Due to high performance requirements, the design of an earth station is quite complicated. This increases the costs and the need for maintenance. VSAT provides a solution to this problem. The key point in VSAT networks is that either the transmitter or the receiver antenna on a satellite link must be larger. In order to simplify VSAT design, a lower performance microwave transceiver and lower gain dish antenna (smaller size) is used. They act as bidirectional earth stations that are small, simple and cheap enough to be installed in the end user's premises. Operation of Very Small Aperture Terminal (VSAT) Networks

VSAT networks are typically arranged in a star based topology, where each remote user is supported by a VSAT. The Earth hub station acts as the central node and employs a large size dish antenna with a high quality transceiver. The satellite provides a broadcast medium acting as a common connection point for all the remote VSAT earth stations. VSAT networks are ideal for centralized networks with a central host and a number of geographically dispersed terminals.

The weaker signal from the remote ES is amplified at the satellite acting as a bent pipe and received by the hub ES. Thus, the lower gain at the uplink is compensated at the downlink by the high performance hub ES. The down side of this arrangement is that when two VSATs need to communicate, two satellite hops are required because all connections must pass through the hub ES node. The data link supported from the hub to the VSAT is typically slower (19.2 kilobits (kbps)) than that in the reverse direction (512 kbps).

The most common MAC schemes used on VSATs are S-ALOHA and TDMA. At the logical link control (LLC) sublayer, a "look back N" protocol with selective reject automatic repeat request (ARQ) retransmission strategy is used. The most common implementation uses a transmission window with N=128 packets and the receiver responds with retransmission requests for only erroneous or missing packets. This protocol combined with Forward Error Correction (FEC) produces reliable data transfers while providing low average delays on satellite links. TCP/IP does not fit well in the VSAT scenario, though it can be supported. The most commonly used network protocol on VSAT links is X.25. DirecPC services

DirecPC is one of the most useful applications of VSAT networks, developed by Hughes Network Systems (HNS) a pioneer in VSAT technology. This service comes with a computer card, a radio frequency (RF) dish antenna (2 ft diameter) equipped with an LNA, and supporting software. All that is required is an IBM compatible computer with a 486 or higher processor and the Windows operating system (OS). The VSAT terminal is installed at an open location. A cable runs from the dish antenna and connects to the personal computer (PC). The receiver processes of demodulation, decoding and demultiplexing are carried out inside the card. The satellite dish can be aimed at the right angle using a software utility package. The DirecPC supports two kinds of services.

  1. Digital Package Delivery:

    This service allows the end user to download files at speeds 100 times faster than that supported by the public telephone network. Large files can be broadcast and received by multiple DirecPC endpoints. The download requests are made using the standard analog modem over telephone lines. The access speed of the satellite link is typically 12 Mbps. Large multimedia files incorporating sound, photos, and video can be transferred to any user on demand.

  2. Turbo Internet:

    With the increasing popularity of the World Wide Web (WWW), the demand for speedy downloads is increasing. The main bottleneck is the analog telephone line, which is incapable of supporting higher data rates. Network congestion on the Internet is another factor contributing to the problem. Using DirecPC, an end user overcomes the telephone line barrier and is capable of receiving data at 400 kbps. This is much faster than typical analog modems (28.8 kbps), ISDN, or T1 leased service (384 kbps). Figure 2 shows a simple functional diagram for this system. The operation of the network is as follows:

    A connection is set up with the local Internet Service Provider (ISP) using the analog telephone line modem.

    All mouse and keyboard actions in the web browser are communicated to the web server on the other end using this link. Instead of directing the data to the requesting node, data is directed to the DirecPC Network Operations Center (NOC). The data is transferred from the NOC to the end user via a satellite link operating at 400 kbps.

Figure 2. DirecPC Service: Sequence of Operations Asynchronous Transfer Mode (ATM) on Satellite Channels

ATM is one of the most promising technologies for the information super-highway. Future networks are required to provide broadband integrated services for voice, video, and data. ATM is capable of providing the requested QoS guarantees typically required by these multimedia services. It is worthwhile to investigate the performance of ATM on satellite channels.

Research efforts are continuing to find a solution to the problem of burst noise on satellite channels. One solution developed by COMSAT is known as the ATM link enhancer (ALE). The ALE module is inserted in the transmitting and receiving paths before and after the satellite modems. The ALE performs selective interleaving of the cells before sending them on a satellite channel. This helps in isolating the ATM cells from burst errors.

4.1.3 Migration Strategy

The satellite communications architecture will be oriented toward wideband transmission rates (up to and including optical character (OC)-1) via transponding satellites with the integration of satellite control and service provisioning into the DISN Information Network Management System (INMS). SATCOM terminals will require bandwidth efficient modulation/coding techniques to achieve virtually error-free performance and will support direct interfaces to terrestrial transmission and switching systems to provide bandwidth on demand. In the far-term, SATCOM capabilities will expand to support trunks operating at data rates up to OC-3. SATCOM trunking requirements must be defined to permit implementation of the required resources. To support the trunking requirements in the far-term, the initial SATCOM gateway configuration deployed in the midterm will be expanded to accommodate the interface between DISN and users of personal communications service/universal personal telecommunications (PCS/UPT) system (e.g. Iridium Systems or Globalstar).

4.1.4 Legacy Systems

There are currently several systems that utilize both the MILSATCOM and commercial satellites. These systems include the Defense Satellite Communication System (DSCS) III, TROJAN, Military, Strategic, Tactical, and Relay (MILSTAR), and the Army Distance Learning Program (ADLP). These legacy systems form the basis from which the future systems and migration plan will be developed. These systems will be the starting point for technology insertion and system development and planning.

4.1.5 System Design Guidance

When deciding on whether to buy, design, or build a single system or complete earth station, there are many items that must be considered in the final costs. When determining whether to build or lease, bandwidth, data rates and costs are some of the items that must be included in the calculations.

4.1.6 Procurement Source Hardware and Software

Table 5 lists just a few of the companies that offer hardware/software equipment and services that could be used to assist in the design, guidance, procurement, operations, and usage of many of the COMSAT products. This list is not all inclusive and the System Engineer (SE) should review additional manufacturer's data on each product.

Table 5. COMSAT Companies

Operators and Manufacturers
American Mobile Satellite Corporation
Comsat Corp.
CTA Corp.
Hughes Electronics Corp.
Motorola Inc.
Orbcomm Global LP
Qualcomm Inc.
Teledesic Corp.
Government and Regulatory Sites
Federal Communications Commission
International Telecommunication Union
National Telecommunications and Information Administration

4.1.7 Areas to be Coordinated and Developed by the System Engineer (SE)

The SE is responsible to ensure all architectural standards are met and to determine what documentation is required such as system design plans, tradeoff analysis, costing, scheduling, and compliance. The SE must ensure that all new equipment programs or existing system upgrades fall within the USAISEC engineering guidelines, which include the following:

  1. Ensuring that any product developed for assigned programs and projects adheres to established USAISEC architectural standards and are fully synchronized and integrated with systems currently fielded as well as those undergoing implementation.
  2. Contacting the Synchronization and Integration Group (S&IG) to arrange a schedule for projects and products to be considered in the critical skill reviews. Providing project and product documentation and details to the S&IG for USAISEC architectural standards compliance review.
  3. Based upon technical review reports received from the S&IG, prepare strategy which shows how the engineering project/product will conform to guidance, standards, and architectures.
  4. Including statements in Statement of Work (SOW), provided by USAISEC, regarding compliance to guidance, architectures, and standards.
  5. Arranging for system demonstration or applying for a waiver from the USAISEC Technical Director. Developing a demonstration plan and coordinating scheduling with the Technology Integration Center (TIC). Providing resources for the demonstration.
  6. Submitting engineering solutions to the USAISEC Technical Director for concurrence that C4I standards are met.

4.1.8 Satellite Link Budget

Link Budget is a generic term used to describe a series of mathematical calculations designed to model the performance of a communications link. In a typical simplex (one-way) satellite link, there are two link budget calculations: one link from the transmitting ground station to the satellite, and one link from the spacecraft to the receiving ground station. Many link budget analysis tools are available to the SE, these tools include:

  1. Link Budget Model
    • Uplink and downlink C/KT.
    • Satellite receive power flux density.
  2. Positional Data Model
    • Earth Terminal to satellite slant range.
    • Earth terminal antenna elevation and azimuth.
    • Uplink and downlink doppler frequency shift.
  3. Benign Atmosphere Attenuation
  4. Clear air attenuation.
  5. Rain fall Attenuation.
  6. Atmospheric signal scintillation.
  7. Modulation and Channel Encoding
  8. Noise equivalent bandwidth.
  9. Modulation spectral efficiency.
  10. Demodulator implementation loss.
  11. Probability of detection of error.
  12. Convolution channel coding gain.
  13. Earth Terminal Model
  14. Antenna model.
  15. Receive system model.
  16. Transmit system model.
  17. Satellite Model.
  18. Uplink signal power.
  19. Downlink signal power.
  20. Transponder signal and noise power sharing.
  21. Transponder uplink power flux.

The following input items are needed to produce a link budget calculation for a spacecraft to ground station link.

4.1.9 Look Angle

The antenna pointing calculation is used to determine the look angle of the earth terminal complex (ETC) antenna. Three items of information are required to complete this calculation. The satellite west longitude which is normally given in decimal form rather than a degree, minute, and second (DD MM SS) format. This number represents the number of degrees west of the Prime Meridian that the spacecraft is located above the equator. Sometimes the number is given as east longitude. In this case, subtract the number from 360 to obtain the west longitude. Next is the north latitude of the ETC location. The format for this location is given normally in the DD MM SS format. Finally the west longitude for the ETC location is needed. It is normally given in decimal format, and if it is given in east longitude, subtract that number from 360 to obtain the west longitude. Once all of these numbers and locations are determined, they need to be entered into a specific calculation.

4.1.10 Satellite Footprint

The projection of the energy of a satellite on the face of the earth is commonly called the satellite footprint. It is actually an aggregation of multiple beams, normally elliptically shaped, and individually steerable. This information reflects the actual spacecraft and the energy patterns of the individual transponders, and should be kept in a database. However, much of the information in the fields is highly technical, and will be supplied by an applications program through which the analyst establishes desired coverage areas, orbit locations, etc. This applications program must generate coverage areas, which reflect both the power source and the antenna sidelobe, for each beam generated by the spacecraft. For this specific coverage area, the aggregated EIRP, antenna gain to noise temperature (G/T), and input flux density contours are generated by multiple elliptical beams which often overlap. Each of these beams will be described by pointing coordinates, major axis angle, minor axis angle, rotation angle, input power density, antenna gain, etc. This allows the engineer to see the visual coverage pattern of a desired service area.

4.2 Satellite Service

Each country has a sovereign right to regulate the use of radio equipment on its territory, including the use of equipment which is in possession of foreigners. The Army Spectrum Manager is responsible to implement the Army spectrum policy and the use of the electromagnetic spectrum consistent with national, international, combined military and multinational agreements. All requests for host nation approval within the frequency spectrum should be addressed to the Army Spectrum Manager. They also represent the U.S. Army at the National Telecommunications and Information Administration (NTIA). The NTIA is at the forefront in developing policies that meet the demands of U.S. industry and Government for scarce radio frequency spectrum. Available radio frequency spectrum is rapidly being allocated and in assigned use. The NTIA's role on behalf of the U.S. is forging international agreements to allocate this spectrum. As part of our national security, the maintenance of a strong U.S. military operating on a worldwide basis mandates the need for international agreement on spectrum allocations. Military operations require internationally agreed upon spectrums for such needs as land, ship, and airborne radar navigation and location systems, satellite communications for tactical operations as well as logistical support needs, surface and air tactical communications, early warning systems, command and control communications, and weapons and armament systems.

4.2.1 Fixed Satellite Service (FSS) in Europe

European Telecommunications Satellite (EUTELSAT): EUTELSAT has developed a series of satellites to  serve Europe's domestic and regional requirements.  The EUTELSAT system comprises seven GEO satellites in seven orbit positions (1 degree, 7 degrees, 10 degrees, 13 degrees, 16 degrees, 21.5 degrees, and 36 degrees east). These satellites support telephony, business services, television and radio distribution, and mobile satellite communications. A TDMA system similar to that used in international telecommunications satellite (INTELSAT) is used for telephony, country to country. The TDMA frame is 2 ms in duration. Time slot assignments are made over eight transponders, with transmitters hopping between transponders. TDMA is by reservation, with a new time-frequency plan introduced about twice a year.Television distribution and even television "broadcast" have provided increased traffic. VSAT networks operate in the FSS and are a growing part of FSS traffic.

The Olympus satellite has FSS transponders for use at KU Band and Ka Band. Italian satellite (ITALSAT) F1 is an FSS satellite with a Ka Band transponder providing on-board switching of signals using a baseband switch matrix. An ITALSAT F3 program is currently underway and would be an operational satellite with multibeam capabilities at both 12/14 GHz and 20/30 GHz. The F3 spacecraft has an on-board signal regeneration and switching capability.

The users, network operators, and manufacturers (UNOM) project is led by Matra Ericsson Telecomm. This activity is only partly concerned with satellite transmission within a broader context of transmission and network technology. The integration of satellite and terrestrial transmissions is one objective. Applications include LAN to wide area network (WAN) interconnection, and interconnection of ATM "islands or "data islands" at high speed. ATM gateway connectivity for mapping of ATM cells, and interconnection and conversion of Ethernet computer networks. The technology involved includes concatenated codes, satellite access protocols, and link data rates of 2 Mbps to 8 Mbps. Satellite transmission is limited to transmission control protocol (TCP).

The Catalyst project is to develop, adapt, or accommodate the round-trip propagation time delay encountered with satellites, integration of satellites, and broadband networks, provision of network management, improvement of link quality, incorporation of a multipoint capability and development of recommendation for adjustment to the International Telephone and Telegraph Consultative Committee (CCITT) standards.

4.2.2 Fixed Satellite Service (FSS) in Japan

Current FSS operations in Japan are provided by the CS-3 series of satellites. These satellites will allow experiments for advanced FSS operations at C and KU Bands. The N-STAR satellite includes Ka, KU, and C Band transponders for FSS. Technology developments for Japan are being tested with multibeam antennas at 20/30 GHz, having four beams and frequency selective surfaces.

4.2.3 Fixed Satellite Service (FSS) in Russia

FSS is currently provided by the GORIZONT system, with transponders at 4/6 GHz and 11/14 GHz. As infrastructure develops, long range planners foresee possibilities for a trunking satellite for interconnecting 50 million users

4.2.4 Mobile Satellite Services (MSS)

Using a pocket sized transceiver with a short, flexible antenna (or a desktop or vehicle mounted transceiver), individual users send and receive wireless data messages. The sender's message goes to the nearest in-view satellite where it is linked to the local gateway for validation and optimal routing to the recipient. The message is then returned to the satellite and stored briefly (until the intended receiver is in view) before delivery to the recipient's transceiver unit. If necessary, gateway earth stations relay messages between satellites for faster delivery. Table 6 below provides a brief MSS functional overview.

Table 6. Functional Overview

4.3 Commercial Satellite Communications Initiative (CSCI)

The CSCI studies demonstrated the applicability of commercial SATCOM to a variety of C3I missions. The new policy guidance establishes the framework to integrate the department's efforts for implementing commercial capabilities and will guide the resulting commercial service investment strategy to ensure a cost-effective augmentation of military satellite capabilities by the department.

The policy states, to the extent operationally and fiscally practical, the DoD will augment its military SATCOM capability with both domestic and international commercial services. To ensure maximum savings are achieved, all acquisition of commercial SATCOM services will be consistent with the approved DISN acquisition strategy and will be acquired through the auspices of the DCCO of the DISA.

As the use of commercial SATCOM increases throughout the DoD, basic interoperability among FSS terminals will be established and maintained through the use of appropriate standards, and in a manner consistent with advancing commercial technology. To the maximum extent practical, all new military transportable FSS earth terminals shall be acquired with the ability to access both the commercial C and KU frequency bands.

In support of this tasking, the department recently hosted a defense wide commercial SATCOM conference, which allowed for the exchange of ideas on the use of commercial satellite systems. DISA will capture this information into a program plan.

4.4 Global Broadcast System (GBS)

The GBS system is being acquired by the GBS Joint Program Office (JPO) to augment MILSATCOM systems and provide a continuous, high-speed, broadcast of high-volume data to units in garrison, deployed, or on the move. The GBS system:

Phase One (present) GBS consists of limited leased commercial satellite services operating at KU Band for concept of operations development, demonstrations, and limited operational support.

Phase Two (1998-2005) will consist of payload packages hosted on UFO satellites 8, 9, and 10 with the downlink broadcast operating at 20.2-21.2 GHz (Ka Band). As only three UFO satellites will be equipped with the GBS Ka Band payloads, the continued lease of COMSAT services at Ku Band will be required to augment UFO GBS where coverage gaps exist and may be required to complement the UFO GBS limited number and size of downlink beams.

Phase Three (beyond 2006): The objective GBS on-orbit capability will provide increased capacity, worldwide coverage, and the capability to broadcast near continuous or time critical information to broadly dispersed users. The specific solution for the GBS long-term capability will be developed in accordance with the DoD MILSATCOM Architecture.

4.5 Interference Reduction Group (IRG) Standard Access

Specific procedures have been developed by the satellite user's IRG and these procedures form the basic process for accessing all U.S. domestic transponders, in both C and KU Band. These procedures include:

Performing the Access. During the access process do not change power, frequency, polarization, or antenna aiming without prior direct instruction from the access control center.

4.6 Transponder Rates

Several companies sell or broker transponder time within CONUS as well as international transponder time. Transponder rates vary by time slots, and transponder usage, for example Prime Time and Non Prime. The average rate for a full transponder in Prime Time is $940.00 per hour; Non Prime time is $840.00 per hour. For half transponder time the cost is $705.00 and $630.00 for Prime and Non Prime respectively.

4.7 Teleports

There are several full-service satellite telecommunications facilities, call teleports, located throughout the U.S. The teleports offer broadcast video, program audio, and voice transmission. Many teleports maintain extensive microwave and fiber optic LAN to connect to and interconnect with local transmission services such as regional bell operating companies and other service providers. Many teleport facilities provide studio productions, video conferencing, and state-of-the-art editing facilities. In a typical network, data or audio to be broadcast is sent to the teleport using dedicated fiber optic lines, single channel per carrier (SCPC) technology, microwave or dedicated phone lines. The data and digital audio signals will then be uplinked and broadcast from the satellite to receiver sites.

4.8 Personal Communications System

The U.S. government has issued six new sets of licenses for building mobile phone networks in the frequency range between 1850 and 1990 Mhz (it is generally referred to as 1900). The country has been divided into a series of geographic areas known as Major Trading Areas (MTA) and Basic Trading Areas (BTA). Auctions for rights to use the first three blocks in the MTAs & BTAs have already been completed. Auctions for the last three licenses are going on right now. All the licenses fall into the group of what are known as Personal Communications Services (PCS).

4.8.1 Transport Mechanisms: TDMA & CDMA

Both TDMA and CDMA are transport mechanisms to move information back and forth between a tower and the phone in a digital mobile phone system. Some companies have decided to name their systems after the transport mechanism they employ.

4.8.2 PCS Technologies: DCS-1900 (GSM), IS-136 and Qualcom's CDMA

DCS-1900 - (Digital Communication Systems at 1900 Mhz) This system is built upon the standards of Global Systems For Mobile (GSM) Communications. GSM is currently deployed in over 128 networks in 77 countries with over 20 million users worldwide. It is the globally accepted standard for mobile communications. DCS-1900 uses TDMA as it's transport mechanism.

IS-136 - This is also a TDMA based system. IS-136 is already being used in limited deployments in the United States. American Telephone and Telegraph (AT&T) has chosen IS-136 as its technology of choice for the PCS licenses it bought in the U.S.

Qualcom CDMA - This is a newer technology. As its name suggests the system was designed by Qualcom and uses CDMA for transport.

4.8.3 IRIDIUM System

The IRIDIUM PCS is a satellite-based, wireless personal communications network designed to permit any type of telephone transmission; voice, data, fax, or paging, to reach its destination anywhere on earth. The IRIDIUM constellation will consist of 66 interconnected satellites orbiting 420 nautical miles above the earth.

4.9 Medium Earth Orbit (MEO) Satellites

During the last few years, technological innovations in space communications have given rise to new orbits and totally new system designs. MEO satellite networks have been proposed that will orbit at distances of about 8000 miles. Signals transmitted from an MEO satellite travel a shorter distance which translates to improved signal strength at the receiving end. This means that smaller, more lightweight receiving terminals can be used. Also, since the signal is traveling a shorter distance to and from the satellite, there is less transmission delay. An GEO satellite requires .25 seconds for a round trip. A MEO satellite requires less than .1 seconds to complete. Worldwide communications to mobile users equipped with vehicle based terminals are currently available through geostationary satellites operating at L-band by International Maritime Satellite (INMARSAT). In order to satisfy a significantly larger market of hand-held terminals a number of satellite systems with global coverage have been proposed. They are all based on a fleet of satellites rotating around the earth in circular or elliptical orbits well below that of the geostationary satellites. The main benefit of non-geostationary orbit satellites is that a smaller distance between the terminal and satellite allows smaller and lower cost satellite transponders and antennas as well as smaller terminals.

4.10 Low Earth Orbit (LEO) Satellites

LEO satellites are divided into three categories: little LEOs, big LEOs, and Mega-LEOs. LEOs will orbit at a distance of only 500 to 1000 miles above the earth. This relatively short distance reduces transmission delay to only .05 seconds and further reduces the need for sensitive and bulky receiving equipment. Little LEOs operate in the 800 Mhz range, big LEOs operate in the 2 GHz or above range, and Mega-LEOs operate in the 20-30 GHz range.

4.11 Modern Satellite Networks

Some present satellite systems and future satellites will incorporate Inter-Satellite Links, on board switching, data buffering and signal processing. The 1990s have been characterized by the trend of reaching the end user with direct to host (DTH) satellite services. Moreover communication satellites are expected to play a crucial role in providing global PCS. With improving performance in satellite receivers and decreasing cost, satellite receivers equipped with dish antennas are now becoming a household commodity.

Satellites are the obvious choice for universal access for data services as they solve the main hindrance towards this goal, distance. Design of modern satellite networks (the so called 3rd generation satellites) is highly influenced by the global trend of user instead of network oriented services. Due to the rapid growth in the cellular market, the telecommunications industry is making large investments in MSS.

This type of service requires:

Quite a few of the above performance requirements go in favor of "small" and "big" LEO satellites. The lower altitude of LEO satellites allows simpler receivers due to smaller attenuation, lesser propagation delays, and also allows easy launch (a high altitude aircraft can accomplish the launch). Due to these reasons, LEO satellites are becoming a candidate (though some systems use MEO satellites) for providing network services. On the downside, the spot beam property results in constellations that need a large number of LEO satellites (and accompanying ES) for global coverage. Managing and coordinating this large number of earth stations as well as complex hand over schemes between satellites is a major drawback for LEO systems. On the other hand GEO satellites can provide both large and narrow footprints with multiple transponders. This combined with the ability to switch data between spot beams are the major factors in favor of GEO system.

The following list presents some salient features of some of the modern satellite networks that use LEO, MEO, and GEO satellite constellations.

Owner Motorola
Satellites 66, 11/orbit
Orbits 900km, 6 polar orbits
Type Big LEO
Round-Trip Delay 10 ms approx.
Start-of-Service 1998
Services Voice, Data (2.4 Kbps), FAX, GPS
Remarks Supports Intersatellite links and handoffs during calls
Web Reference



Bill Gates, Craig McCaw




700 km


small LEO

MAC method


Round trip delay

<8 ms approx.

Start of service



Voice, Data up to 2Mbps


Phased array antennas, installation costs - US $9,000 !!

On-line reference





10, 2 spares


8-10000 km



MAC method


Round trip delay

200 ms approx.

Start of service



Voice, Data (2.4Kbps), FAX, GPS


4500 telephone channels per satellite

On-line reference



Loral, Qualcomm


48 (8 spares)


1400 km, inclined



MAC method


Round trip delay

10 ms approx.

Start of service



Voice, Data (9.6 Kbps), FAX Location services


No Satellite handovers, elliptical spot beams

On-line reference







10370 km



MAC method


Round trip delay

120 ms approx.

Start of service



Voice, Data (9.6Kbps), FAX, GPS


No handover, steering antenna eliminates spot beam handover

On-line reference



Comsat etc.




36000 km



MAC method


Round trip delay

500 ms

Start of service



Voice, Data (2.4 Kbps), FAX, Telex


Allows a 6.4Kbps voice channel, suitcase terminal

On-line reference

4.11.1 INMARSAT B High Data Rate Gateway Switch

The INMARSAT-B system supports high data rate (HDR), 56/64 kbps services to mobile users. The HDR gateway switches (HGS) for COMSAT mobile communications (CMC) allow CMC to extend the terrestrial ISDNs offered by regional Bell operating companies and interexchange carriers (IXC) to be available to mobile terminals anywhere in the world via CMC's land earth stations (LES) in Connecticut, California, and Malaysia. The HGS also allows mobile-to-mobile HDR calls within the same ocean region, and from any ocean region to any other, worldwide. The gateway switch complements the existing CMC service offerings of INMARSAT-B low-speed (9.6 kbps) voice, data, and facsimile.

The HGS interfaces to the access and control equipment (ACE) within the CMC LES for the exchange of signaling messages and with HDR channel units for receiving and transmitting data to the mobile terminal. For connectivity to the fixed user, the HGS interfaces to switched 64 kbps IXC networks in accordance with the primary ISDN specifications defined by the International Telecommunication Union-Telecommunications (ITU-T) Sector and the American National Standards Institute (ANSI). The HGS compensates for all incompatibilities between the D-channel signaling to the terrestrial network and the signaling to the ACE/INMARSAT-B terminals. Inter-HGS connectivity is also supported to minimize terrestrial connectivity requirements at each HGS site and to support HGS calls between mobile terminals in different ocean regions.

4.11.2 Intelligent Networks

Intelligent networking will play a key role in future mobile satellite communications. By providing the infrastructure needed to manage sophisticated mobility services in both wired and wireless networks, intelligent networking will allow mobile satellite service providers to extend into their networks the services currently offered in terrestrial networks. A study was conducted of emerging intelligent network architectures and standards, focusing on their application to mobile satellite service. Services supported by the current Bellcore and ITU capability sets were investigated and the potential for using intelligent networking to perform mobility management functions in next-generation mobile satellite systems was assessed.

4.11.3 Asynchronous Transfer Mode (ATM) over Satellite

A series of experiments and demonstrations of ATM via satellite have been conducted for the DISA under the CSCI. The ATM communications standard defines the efficient transport of multimedia information and offers bandwidth-on-demand capacity to system users. During the experiment phase, tests were undertaken to quantify the impact of satellite propagation delay and bit error characteristics on the operation of the physical layer convergence protocol (PLCP), ATM, the ATM adaptation layer (AAL), the service-specific connection-oriented protocol (SSCOP), and the TCP over 45-Mbps satellite links. This is an evolving technology.

4.11.4 Advanced Very Small Aperture Terminal (VSAT)

Recent developments in satellite and communications technologies, along with increasing demand for advanced user services, have created new opportunities for advanced satellite-based networks. Ongoing Research and Development (R&D) covers a broad spectrum of satellite networking technologies. These include TDMA, high-density programmable digital hardware design, advanced modem and codec design, data networking and satellite-efficient protocols, LAN/WAN interconnect technologies, ISDN, frame relay, ATM, real-time software development, and advanced network management systems. This R&D has led to the rapid development of several key next-generation satellite networks.

These networks offer the low cost and small size VSAT; data rates from 64 kbps to 16 Mbps, previously found only in high-end systems; and the functionality and flexibility of dynamic bandwidth on demand, ISDN, packet switching, and LAN interconnection.

4.11.5 Second Generation Time Division Multiple Access (TDMA)

The second generation INTELSAT 120 Mbps TDMA terminal currently under development reduces the large, 12-rack, first-generation equipment into a single rack. In addition, the terminal's efficiency, operation, monitoring, and self-testing are improved.

A second-generation operation and maintenance center (OMC) for use with first generation INTELSAT TDMA equipment has been developed. Employing state-of-the-art display and workstation technology, the new OMC has dramatically reduced operator errors and significantly decreased equipment size.

In conjunction with the second-generation OMC, a new direct digital interface (DDI) has been developed for use with first-generation TDMA equipment. The DDI permits the direct connection of 2.048 Mbps primary multiplex carriers, from switching centers or digital circuit multiplication equipment (DCME), to the first-generation INTELSAT TDMA terminal. The DDI can accommodate as many as 40 on-line, 2.048-Mbps primary multiplex carriers and provides 1-to-N redundancy, while significantly decreasing equipment size.

4.12 Research Fields

The role of satellites is changing from the traditional telephony and TV broadcast services to user oriented data services. This trend is expected to continue in the future. For this reason, 3rd generation MSS will use smart satellites that will incorporate functions such as switching, buffering, and beam switching in addition to signal reproduction. Satellite data services on existing GEO satellite systems, like VSAT, will continue to compete with the terrestrial options such as telephone line and fiber links. Small and large LEO constellations are expected to become a candidate in the cellular market. At the same time the popularity of GEO systems is not expected to diminish. In order to meet the increasing demand for real time traffic, channel access and link layer protocols will have to be optimized to ensure smooth operation over the satellite channel. TDMA and CDMA appear to be two of the strongest candidates for the MAC protocol. The evolution of satellite technology along with the fixed and mobile terrestrial communications is expected to merge into Universal Personal Telecommunications (UPT)

4.12.1 Wide Area Communications Server.  WACS allows customers to significantly improve network performance and reduce the cost of WAN data links. The WACS was developed for National Aeronautic and Space Administrations (NASA) Jet Propulsion Laboratory for use in its Deep Space Information Network. With its data compression feature, the WACS can double or triple the effective link rate, thereby, reducing the need for NASA to upgrade expensive leased lines. Even with satellite links operating at BER of 10-4, with the TSP, the WACS provides 70 to 80 percent throughput before compression.

4.12.2 Data Communications. With the increasing use of personal computers, workstations, and LANs, data communication is one of the fastest growing segments of the communications market. The X.75 protocol is used to interconnect national public data networks. Converter units developed for INTELSAT provide for efficient use of the protocol over satellite links. As part of this project, a satellite-efficient protocol was developed which incorporates multiselective reject error recovery to provide throughput efficiency greater than 75 percent, even in the presence of degraded link BER conditions (10-5). The protocol converter also incorporates an advanced multiprocessor architecture that can support multiple X.75 links operating at 2.048 Mbps.

4.12.3 Advanced Communications Technology Satellite (ACTS) Frame Relay. The ACTS frame relay access switch (FRACS) provides a bandwidth on demand (BOD) frame relay interface to NASA ACTS TDMA network. The FRACS transports LAN packets over ACTS TDMA circuits, and dynamically allocates ACTS circuits between different pairs of sites, based on an adaptive, rate-based bandwidth management scheme.

4.12.4 Integrated Services Digital Network (ISDN). The ISDN Satellite Switch (ISS) provides high-quality, cost-effective ISDN services via satellite. Efficient integration of ISDN with a satellite communications network is achieved by using powerful out-of-band ISDN signaling and by exploiting the strengths inherent in satellite systems, their accessibility to a widely dispersed community of users, and the multipoint/broadcast nature of satellite communications channels. The ISS is intended to demonstrate the feasibility of this integration. The effectiveness of carrying ISDN traffic over satellites was demonstrated through field trials using the ISS and the American Telephone and Telegraph (AT&T) Integrated Access Terminal (IAT). The functionality of the ISS, the ISDN access capability, resource allocation on demand, better transport through the satellite network, and switching directives all complement the IAT, which packetizes, compresses, and cross-connects different types of traffic.

4.12.5 ISDN, SDH and ATM via INTELSAT. INTELSAT has ensured that INTELSAT's global satellite communications system can function as a subnetwork of developing international public telecommunications networks such as ISDN, future broadband ISDN, B-ISDN, and synchronous digital heirarchy (SDH) transport network infrastructures. They developed top-level specifications for satellite subnetworks and their functional subsystems, and analyzed the performance of the subnetworks. Details of the functional integration between the satellite subnetworks and the interconnected ISDN terrestrial network elements were also developed. In a related activity, the development of international standard Q.768, which governs signaling between a satellite subnetwork and an international ISDN gateway was initiated. Prior to Q.768, if an international call request arrived at an outgoing ISDN switching center, the switch permanently assigned an appropriate trunk between the outgoing and incoming international switches. As a result, satellite capacity could lie idle, depending on traffic intensity. Q.768 signaling allows international switching centers to request a satellite circuit on a per-call basis.

4.12.6 Mobile Satellite/Terrestrial Interworking. Mobile communications is another fast-growing area of telecommunications. Research is ongoing in this area on mobile network architectures and the interoperation of terrestrial and satellite mobile communications systems. Researchers have evaluated the networking capabilities of the European GSM cellular system and the North American digital cellular system, including the respective GSM mobile application port (MAP) network signaling necessary for roaming and call handoffs. These networking capabilities, together with intelligent network functionality, will provide for the extension of personal communication services to satellite networks.

4.13 Transmission Security

The design and engineering of COMSAT systems must be completed with transmission system and network security paramount in the planning. All Army systems must demonstrate that they meet the applicable profile described in both AR 380-19 and the DoD Trusted Computer System (TCS) Evaluation Criteria Standard, DoD 5200.28-STD. Security requirements and engineering should be determined in the initial phases of design. The determination of security services to be used and the strength of the mechanisms providing the services are primary aspects of developing the specific security architectures to support specific domains. Section 6 of the JTA-Army is used after operational architectural decisions are made regarding the security services needed and the required strengths of protection of the mechanisms providing those services. Section 6 of the JTA-Army can also be used to assess the relevance of standards that can be met with evaluated commercial and government-provided components and protocols. The JTA-Army can be used as a tool to evaluate elements of the system architecture regarding operational security requirements, standards compliance, and interoperability with other systems. The AIS Design Guidance, Information Systems Security provides guidance and should be reviewed for appropriate TCS design guidance.

4.13.1 The Multilevel Information System Security Initiative (MISSI)

MISSI is a network security initiative, under the leadership of the National Security Agency (NSA). It provides a framework for the development and evolution of interoperable, complementary security products to provide flexible, modular security for networked information systems across the DII and the National Information Infrastructure (NII). The purpose of MISSI is to make available an evolving set of solutions that provide secure interoperability among a wide variety of missions that compose the DII. The MISSI approach is to work closely with customers to provide systems security engineering support to understand and meet the users' present and future needs. The MISSI security solutions provide appropriate security based on the threats to the customer's specific environment.

MISSI Firewalls: Firewalls provide protected connections between enclaves with sensitive but unclassified (SBU) information and potentially malicious networks. Firewalls with FORTEZZATM identification & authentication (I & A) permit controlled access to the SBU enclave from users outside the enclave, further enhancing security. Common types of firewalls are screening routers (packet-filtering systems), application-level gateways (proxies and forwarders), and hybrids of routers and application-level gateways.

4.13.2 Bulk Encryption Systems

The following products have provided reliable protection and are still available for use.

The KG-84 is a dedicated loop encryption device that encrypts and decrypts teletypewriter and digital data traffic. It supports data rates from 50 bps to 9.6 Kbps and RS-232, RS-422/423, and RS-449 interfaces.

KG-84A. The KG-84A is general purpose encryption equipment that encrypts and decrypts teletypewriter and digital data traffic on digital links between various types of input/output (I/O) devices, including PC-type computers and facsimiles. It is an improved version of the KG-84. It supports data rates from 50 bps to 32 Kbps and RS-232, RS-422/423, and RS-449 interfaces.

KG-84C - The KG-84C is general purpose telegraphy encryption equipment. It encrypts and decrypts teletypewriter and data traffic on dedicated links between various devices and a variety of modems. The KG-84C supports data rates from 50 bps to 32 Kbps and interfaces for V.10, RS-422/RS-423, RS-449, and RS-232C.

Embeddable KG-84 Communications Security (COMSEC) Module (KIV-7). The KIV-7 is interoperable with the KG-84A/C to encrypt/decrypt data communication links among users of PCs, workstations, and facsimile equipment. It is a half-height disk-drive size that makes it configurable as embeddable desktop or multiunit rack mount installation. It supports data rates from 50 bps to 288 Kbps and RS-232, RS-422/423, and RS-449 interfaces.

KG-94 Family. The KG-94 family consists of KG-94/94A/194/194A Trunk Encryption Devices. The KG-94 family has full duplex synchronous key generators used primarily for bulk encryption of multichannel traffic. The KG-94/194 is designed for use in fixed plant sheltered environments. The KG-94A/194A is designed for use in ground mobile tactical environments. The KG-94 family supports data rates from 9.6 Kbps to 13 Kbps.

KG-95 Family. The KG-95 is a family of full duplex, fixed plant, bulk encryption/decryption key generators that are approved for processing all classifications of traffic. There are three equipment configurations available. The KG-95-1 is the general purpose version of the KG-95, capable of operating at any data rate between 10 and 50 Mbps. The KG-95-2 operates only at the DS-3 data rate of 44.736 Mbps. The KG-95R consists of two KG-95-2s providing a hot spare capability.

The KG-189 operates with SONET. It is intended for use in securing a single SONET trunk which feeds a communications complex. A "light-in, light-out" device, the KG-189 supports optical transport at both the RED and BLACK interface to the communications system. OC-3, OC-3c, OC-12, OC-12c, and OC-48 rates and protocols will be supported in the initial KG-189 release; a modular architecture ensures future support at OC-192 and beyond.

List of Acronyms

AAL ATM adaptation layer
ABR available bit rate
ACE access and control equipment
ACTS advanced communications technology satellite
ADLP Army distance learning program
AIS Automated Information Systems
ALA ATM link accelerator
ALE ATM link enhancer
ANSI American National Standards Institute
ARQ automatic repeat request
AT&T American Telephone and Telegraph
ATM Asynchronous Transfer Mode
BCN/RM backward-explicit congestion notification via resource management
BER bit error rate
B-ISDN Broadband ISDN
BOD bandwidth on demand
BOM Bill of Materials
BTA basic trading areas
C2 Command and Control
C2I Command, Control, and Intelligence
C3I Command, Control, Communications, and Intelligence
C4 Command, Control, Communications, and Computers
C4I Command, Control, Communications, Computers, and Intelligence
C4IFTW C4I for the warrior
CCITT International Telephone and Telegraph Consultative Committee
CDMA code division multiple access
CINC Commander in Chief
CJCSI Chairman of the Joint Chiefs of Staff Instructions
CM centimeter
CMC COMSAT mobile communications
C/N carrier to noise
CNR combat net radio
COE common operating environment
COMSAT commercial satellite
COMSEC communications security
CONUS Continental United States
COTS commercial off-the-shelf
CSCI Commercial Satellite Communications Initiative
CSMA/CD carrier sense multiple access/control detection
CSU channel service unit
CTF Command Task Force
DAMA demand assigned multiple access
DCCO Defense Commercial Communications Office
DCME digital circuit multiplication equipment
DD MM SS degree, minute, second
DDI direct digital interface
DII Defense Information Infrastructure
DISA Defense Information Systems Agency
DISC4 Director of Information Systems for C4I
DISN Defense Information System Network
DLC data link control
DMS Defense Message System
DoD Department of Defense
DoDD DoD Directives
DoDI DoD Instructions
DSCS Defense Satellite Communications System
DSU digital service unit
DTH direct to host
EC/EDI electronic commerce/electronic data interchange
ECI electronic commerce infrastructure
EIRP effective isotropic radiated power
ES earth station
ESA European satellite Agency
ET Earth Terminal
ETC Earth Terminal Complex
EUTELSAT European telecommunications satellite
FDMA frequency division multiple access
FEC forward error correction
FRACS frame relay access switch
FSS Fixed Satellite Service
GBS Global Broadcast System
GCC Global Control Center
GCCS Global Command and Control System
GCSS Global Combat Support Systems
GEO geosynchronous orbit
GHz gigahertz
GOTS Government off-the-shelf
GSM Global System for Mobile
G/T antenna gain to noise temperature
GTE General Telephone and Electric
HDR high data rate
HGS HDR gateway switches
HNS Hughes Network Systems
I&A identification & authentication
IAT integrated access terminal
IDM Information Dissemination Manager
IEW Intelligence/Electronic Warfare
IF intermediate frequency
IITS Installation Information Transfer System
INE In-Line Network Encryptor
INMARSAT International Maritime Satellite
INMS information network management system
INTELSAT International Telecommunications Satellite Organization
I/O input/output
IRG interference reduction group
ISDN Integrated Services Digital Network
ISP Internet Service Provider
ISS ISDN Satellite Switch
ITALSAT Italian satellite
ITU International Telecommunications Union
ITU-T International Telecommunication Union-Telecommunications Sector
IXC interexchange carriers
JIEO Joint Interoperability Engineering Organization
JPO Joint Program Office
JTA Joint Technical Architecture
JTA-Army Joint Technical Architecture-Army
JTF Joint Task Force
Kbps kilobits per second
Kg kilogram
LAN local area network
LEO low earth orbit
LES land earth stations
LNA low noise amplifier
LLC logical link control
LOS line of sight
MAC media access control
MAP mobile application port
Mbps megabits per second
MCEB Military Communications-Electronics Board
MEO medium earth orbit
MILSATCOM Military Satellite Communications
MILSTAR Military Strategic, Tactical, and Relay
MISSI Multilevel Information System Security Initiative
MS millisecond
MSS mobile satellite services
MTA major trading areas
NASA National Aeronautics and Space Administration
NES Network Encryption System
NII/GII National and Global Information Infrastructure
NMS network management station
NOC network operations center
NSA National Security Agency
NTIA National Telecommunications and Information Administration
OC optical character
OCONUS Outside Continental United States
ODISC4 Office of the Director of Information Systems for C4I
OMC operations and maintenance center
OMT ortho mode transfer
OS operating system
OSI open system interconnect
PC personal computer
PCS personal communications service
PCS/UPT personal communications service/universal personal telecommunications
PF2K Post-FTS-2000
PIP primary injection point
PLCP physical layer convergence protocol
POC point of contact
PPSB power projection and sustaining base
PRI primary rate interface
PRMA packet reservation multiple access
PSTN public switched telephone network
QA quality assurance
QoS quality of service
R&D Research & Development
RCC Regional Control Center
RF radio frequency
S&IG Synchronization and Integration Group
SATCOM Satellite Communications
SBM Satellite Broadcast Manager
SBU sensitive but unclassified
SCPC single channel per carrier
SDH synchronous digital hierarchy
SDNS Secure Data Network System
SDP System Design Plan
SE System Engineer
SHADE shared data environment
SMI Security Management Infrastructure
SONET Synchronous Optical Network
SOW Statement of Work
SP3 Security Protocol 3
SSCOP service-specific connection-oriented protocol
TAFIM Technical Architecture Framework for Information Management
TCP Transmission Control Protocol
TCP/IP Transmission Control Protocol /Internet Protocol
TCS Trusted Computer System
TDMA time division multiple access
TIC technology integration center
TIM Theater Information Manager
TSP time sequence protocol
U.S. United States
UFO UHF Follow On
UHF Ultra High Frequency
UNIX Universal Information Exchange
UNOM users, network operators, and manufacturers
UPT Universal Personal Telecommunications
URL Uniform Resource Locator
USACECOM U.S. Army Communications-Electronics Command
USAISEC U.S. Army Information Systems Engineering Command
USASC U.S. Army Signal Command
VCI virtual circuit identifier
VSAT very small aperture terminal
WACS wide area communications server
WAN wide area network
WIN Warfighter Information Network
WSTA Weapons System Technical Architecture
WWW World Wide Web


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