Chapter 1. Telecommunication Basics


The "Telecommunications Handbook for Transportation Professionals" was originally published in 1987 as the "Communications Handbook for Traffic Control Systems". The first (and only) update was initiated in 1991, and published in 1993. Given the significant advances in the technology of telecommunications, and the complexities of Traffic and ITS systems deployment its is necessary to create a new (rather than a revision) handbook providing a broader view of telecommunications technology as applied for traffic and transportation purposes. This handbook provides a broad overview of telecommunications technology and history.


The "Telecommunications Handbook for Transportation Professionals" is intended to provide an introduction to telecommunication technology and process for transportation engineers and project managers involved in the design and deployment of traffic signal and freeway management systems. The handbook can be used as a resource that provides an overview of the various technical issues associated with the planning, design, operation, and management of a communications system. It is intended to provide the user with a better understanding of applied communications technology and the considerations for use in freeway and surface street networks.

The intended audience is transportation professionals who may be involved with, or responsible for any phase in the life cycle of a traffic signal or freeway management control network. This includes all public or private "practitioners" (e.g., managers, supervisors, engineers, planners, or technicians) involved with any issue or decision (e.g., policy, program, funding, or system implementation) and who may directly or indirectly influence the performance of traffic on local arteries or freeway facilities. These activities may include, but not be limited to, planning and design, operational strategies, programs, and services that support continuous management of travel and control of traffic, and the technology infrastructure to provide these capabilities.

Relationship to National Architecture

Telecommunications systems as part of the National ITS Architecture are the connecting pathways that bind the various elements of traffic signal, freeway management, and transportation systems together. The National ITS Architecture "sausage diagram" indicates how these elements are bound together, but does not specify the telecommunication system. The developers of the National ITS Architecture understood that each telecommunication system would be uniquely designed to meet the needs of each project.

The significant diversity of communications technologies and the overall complexity of traffic signal, freeway management, and transportation systems have created a need for traffic and transportation professionals to implement the Systems Engineering Process (SEP). This handbook provides a summary (Chapter 4) of how to apply an SEP to the development of a telecommunications system, for traffic signal and freeway management systems development.

Open System Interconnection Model (OSI)

The OSI model is an International Standards Organization (ISO) standard that defines a framework for implementing telecommunication and software protocols. The OSI model is organized into seven hierarchal layers. Control is passed from one layer to the next starting at the application layer and proceeding down to each successive layer and back as required for any given process. Most of the functionality of the OSI model exists in all communications systems – however, two or three layers may be combined into one. The most significant role of the OSI model is to serve as a reference for the development of other protocol stacks. A detailed explanation of the OSI Model is provided in the Addendum section of this handbook. Table 1-1, provides a list of the OSI Model Protocol Stack.

Table 1-1: OSI Protocol Stack
Layer # Protocol
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

Telecommunications hardware generally utilizes layers one and two of the protocol stack. Modems, multiplexers, bridges, routers, switches, media converters, codecs, etc. are examples of the types of devices that exist at the physical and data link layers of the protocol stack. All media and most of the protocol converters are considered as layer one items. Some communication hardware devices are designed to operate at higher layers. A network router is often referred to as a "layer 3 router". This is one of the few examples of communication hardware that is designed to function above layer two. Most communication systems are not designed using the OSI protocol stack. This is because the hardware vendors have already taken the OSI model into consideration for the design of their products. The RS232 and RJ45 connectors built into the 2070 traffic controller are already layer one compliant. Serving as a protocol stack model, OSI is used as the reference for the development of most other communications protocols. The National Transportation Control Interface Protocol (NTCIP) (1) has a specially developed protocol stack based on the OSI model.

Notice (figure 1-1) that the NTCIP protocol stack is modeled on the OSI stack, and has embedded telecommunication standards. Communication system designers would simply use the pre-defined telecommunication standards. However, developers of software control systems must be acutely aware of the NTCIP protocol stack. NTCIP and its role in the development of a communication system is explained in Chapter 3.

diagram of NTCIP standards framework showing the relationship of the protocol layers of the NTCIP standard

Figure 1-1: Diagram – NTCIP Standards Framework

Telecommunications History

The history of modern-day communications technology can be said to have started when Samuel Morse invented the wireline telegraph in 1832. However, it was Alexander Graham Bell's invention of the telephone, in 1874, that led to the development of our present day communications technology. Morse had simply created a way for humans to extend their ability to transfer information – instantly – over great distances. Bell gave us the ability to have the most intimate form of communication over distances – the use of our voices.

The concept of the telephone instrument – and the system that allows it to work – was so strong that most communication technology during the past 125 years was developed to support an efficient voice communication network. It wasn't until 2004 that major telecommunication carriers announced the need to develop, and support, a network designed for the purpose of transporting digital data.

The wireless telegraph (now referred to as radio) was invented by Guillermo Marconi in 1896 (2). When wireless communication was finally able to be used for voice transmission, it emulated the telephone system.

From 1874 to 1980, communication networks around the world were constructed to facilitate the efficient and economical transmission of voice conversations. Multiplexing and digital transmission systems were developed to "cram" more voice conversations into the existing copper wire communication facilities.

The Internet, first developed in 1973 as a project for the U.S. Department of Defense Advanced Research Projects Agency (ARPA), initiated a profound change in the future development of communications networks and technologies. Originally called the Arpanet – linking several Universities and research laboratories – it evolved into the world wide web (WWW). During this period, there were a number of significant technology advances and government enforced corporate reorganizations that helped to change the direction of communications systems development:

  1. Computing and communications technologies were provided a big boost by the invention of the integrated circuit (IC) in 1959. The IC permitted development and manufacture of smaller and more automated communication devices at a very low cost.
  2. The Carterphone Decision, by the U.S. Supreme Court, in 1968, made it possible for the connection of non-telephone company owned devices (until this point, only devices owned and operated by the telephone companies were permitted).
  3. In the 1970s, fiber strands were first used as a communication medium.
  4. In 1983, the U.S. Supreme Court mandated reorganization of AT&T was enforced.
timeline bar that delineates the dominance of the voice-based networks from the invention of the telephone in 1876 until 1995 and the start of the change-over from voice centric networks to data centric networks starting in 1995

Figure 1-2: Telecommunication Timeline

New inventions coupled with increasing business and consumer demand for computer and data communication services forced a change in the nature of the development of communications networks. By 1995, most installation of communications networks was devoted to the efficient transmission of data generated by computers. However, these networks were still based on a voice communication design.

The development and introduction of broadband data communications standards (IEEE 802 Series (3)) helped to create a demand for communications networks designed to support data communications.

By 2003, wireless (cellular telephone) networks were available to almost every location of the United States (remote wilderness areas still lack coverage). According to the Cellular Telecommunications & Internet Association (CTIA), there were more than 148 million wireless subscribers, and 92% were using digital service.

A timeline of the support for traditional voice transmission services versus data transmission services might appear as follows:

By 2003, 63% of Americans use the internet, and 31% of home users have broadband access (4). In early 2004, Verizon, announced a major upgrade of its basic telephone network to support "Internet Telephony" or Voice over Internet Protocol (VoIP) (5). Southern Bell Corporation (SBC) also announced similar upgrades for its networks.

Handbook Organization

The Telecommunications Handbook for Transportation Professionals is organized to provide the reader with a logical flow of information with a description of various communication terms and technologies that are commonly used (or considered) for the deployment of Freeway Management and Traffic Signal systems. Technical descriptions are kept at a minimum engineering level to provide non-communication professionals with a basic understanding of the technologies.


2. Historically, Marconi is credited with the invention of the wireless telegraph, however, a landmark June 21, 1943 supreme court decision stated that Marconi had violated Nikola Tesla's patents for wireless communications. See "United States Reports; Cases Adjudged in the Supreme Court of the United States," Vol. 320; Marconi Wireless Telegraph Co. of America v. United States, pp. 1-80.


4. Pew Trust – "Internet & American Life", December 2003. –

5. Ivan Seidenberg, CEO Verizon, at the Consumer Electronics Show, Jan 2004.

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