Manual TABLE OF CONTENTS Module 9. TABLE OF CONTENTS MODULE 9. COMMUNICATIONS TABLE OF CONTENTS 9.1 INTRODUCTION ............................................ 9-3 MODULE OBJECTIVES ............................................. 9-4 MODULE SCOPE ................................................... 9-4 9.2 DECISION PROCESS ....................................... 9-4 PROBLEM IDENTIFICATION ........................................ 9-5 IDENTIFICATION OF PARTNERS AND CONSENSUS BUILDING ........... 9-8 ESTABLISH SYSTEM GOALS AND OBJECTIVES ....................... 9-9 ESTABLISH PERFORMANCE CRITERIA ............................... 9-9 FUNCTIONAL REQUIREMENTS ..................................... 9-10 DEFINE FUNCTIONAL RELATIONSHIPS, DATA REQUIREMENTS, AND INFORMATION FLOWS .................................... 9-12 Logical ........................................................ 9-12 Physical ....................................................... 9-12 Central ..................................................... 9-14 Distributed .................................................. 9-16 Trunking ................................................... 9-16 Backbone ................................................... 9-16 Multimedia .................................................. 9-18 IDENTIFY AND SCREEN TECHNOLOGIES ............................ 9-18 IMPLEMENTATION ............................................... 9-23 National ITS Standards ........................................... 9-23 Installation ..................................................... 9-26 9.3 TECHNIQUES AND TECHNOLOGIES ................... 9-26 LAND-LINES ..................................................... 9-26 Twisted-Wire Pairs ............................................... 9-27 Coaxial Cable ................................................... 9-31 Fiber Optic ..................................................... 9-35 WIRELESS ....................................................... 9-39 Area Radio Network ............................................. 9-39 Microwave ..................................................... 9-42 Spread Spectrum Radio ........................................... 9-43 Cellular Radio .................................................. 9-45 Packet Radio ................................................... 9-48 Satellite Transmission ............................................. 9-50 9.4 LESSONS LEARNED ....................................... 9-51 DESIGN PRINCIPLES .............................................. 9-51 OWNED VERSUS LEASED COMMUNICATIONS ....................... 9-53 9-1 Manual TABLE OF CONTENTS Module 9. TABLE OF CONTENTS NTCIP ........................................................... 9-56 SHARED RESOURCE PROJECTS .................................... 9-59 TRANSIENT PROTECTION ......................................... 9-63 COMMUNICATIONS WITHIN THE CONTROL CENTER ................. 9-64 9.5 REFERENCES .............................................. 9-65 9-2 Manual TABLE OF CONTENTS Module 9. TABLE OF CONTENTS MODULE 9. COMMUNICATIONS Figure 9-1. Fiber Optic Cable Installation in Fort Worth, TX. 9.1 INTRODUCTION of information to be transferred from the field components and the control center: (1) The communications subsystem is one of the most critical and expensive elements of a • Commands to the various field freeway management system. The function components. of the communications system is to link the devices in the field with the operating • Data from the system detectors and personnel in the control center. It is the sensors. backbone of the entire freeway management system because it allows the following types • Status checks of field equipment to detect malfunctions. 9-3 Manual TABLE OF CONTENTS Module 9. TABLE OF CONTENTS Typically, the communications system MODULE OBJECTIVES accounts for approximately 25 percent of the total capital costs associated with a freeway The objectives of this module are as follows: management system. Failure to plan, design, and properly maintain the communications • To outline the process that can be system guarantees the entire freeway followed in planning and designing a management system will have problems in new freeway management system or achieving its operational goals and updating or modifying an existing objectives. Poor planning and installation of freeway management system. the communication system can also result in high operating and maintenance costs. To • To highlight the different types of avoid problems with the communications communication technologies that are system, system planners, designers, and commonly used in a freeway operators must be familiar with existing and management system. emerging communication technologies and system architectures. • To provide insight into the issues associated with planning, designing, Three general types of communications constructing, operating, and maintaining systems are used in a freeway management a communications system in a freeway system: management system. • A communications system allowing the MODULE SCOPE transfer of surveillance data and control commands between field devices and the The focus of this module is on the decision control center. process for planning, designing, and selecting a communications system for a • A communications system allowing the freeway management system. It is intended computers within the control center to to help system designers and traffic transfer data and displays between each engineers make informed decisions about other. communications systems. It is not intended to provide detailed information about the • A communications system allowing the operation of different communications operators in the control center to systems or technologies. For more detailed exchange data and information with information about the different other operators and field personnel communications technologies, the reader outside the control center. should consult the Communications Handbook for Traffic Control Devices and This module focuses on the first type of the Traffic Control Systems Handbook.(1,2) communications system (i.e., the communications system needed to transfer 9.2 DECISION PROCESS surveillance information and data, and control commands between the field devices As with the planning and design of the other and the control center). For information on functional elements of a freeway the other types of communications systems, management system, a systems engineering the reader is referred to Module 10. approach can also be applied to the planning, design, and use of a communications system 9-4 Manual TABLE OF CONTENTS Module 9. TABLE OF CONTENTS for a freeway management system. An • The relative importance of the overview of the systems engineering information and how a loss of approach is presented in Module 2. The communication from each device would information in this section highlights some affect the overall operation of the important issues that need to be discussed, system. evaluated, and decided upon as part of the systems engineering process. The user is Table 9-1 summarizes some physical, encouraged to consult other reference institutional, and other issues that might materials, such as the Communications affect the planning and design of the Handbook for Traffic Control Systems for a communications system for a freeway detailed discussion of the technical aspects management system. associated with planning and designing a communications system for traffic control One question that must be addressed in applications. (1) planning and designing a communications system is the type of data that will be PROBLEM IDENTIFICATION transmitted over the communications medium: voice, data, video, or a The first step in planning and designing a combination of all three. A communications communications system for a freeway medium is the pathway over which a signal management system is to identify the is transmitted (i.e., twisted wire pair, coaxial physical, institutional, and other factors that cable, fiber, radio, etc.). “Voice” is the might affect the design of the chosen term for audio signals, since the communications system. System designers impetus for modern communications systems and planners need to collect information on was the need to transmit vocal messages the following attributes and characteristics over the telephone. While some freeway about each of the other elements and management applications, such as Highway subsystems that will be supported by the Advisory Radio, still depend on voice communications system. The types of communications, data is the most general information that should be gathered include type of information transmitted in a the following: communications system in a freeway management system. Digital data is the most • The type of data that will be transmitted common form of transmitted information in by each field device. today’s communications systems. With digital data, information is represented by a • The content and format of the data combination of bits, where a bit can assume transmitted. one of only two states: “0” or “1.” Digital data can be physically transmitted as voltage • How much processing of data will occur differences between pairs of wires, light in the field devices and where this intensities in an optical fiber, frequencies in processing will occur. a transmission line, or phases of a radio wave. Video is animated imagery and • The total number of field devices and represents the most demanding form of data where they will be situated. transmission.