Cities and Their Vital Systems Infrastructure Past, Present, and Future (1988) / Chapter Skim
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10 Combining Communications and Computing: Telematics Infrastructures
10 Combining Communications and Computing: Telematics Infrastructures
Pages 233-248
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From page 233... ...
A Wall Street Journal reporter types a story into a word processor in New York, and the paper is printed and published in Chicago, San Francisco, and Miami the same day as in New York. Automobile manufacturers tailor production schedules to fill dealers' orders for cars with specific arrangements of features.
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From page 234... ...
COMPONENTS OF A TELEMATICS INFRASTRUCTURE Computer functions have been used in communications since about 1900, first with the introduction of the dial-controlled switch to make automatic telephone connections and, more obviously, since the 1950s when computers were attached to the telephone network to measure usage and computer charges. (The switching and billing computers, however, are internal to the network and are not accessible to the telephone user after a connection is made.)
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From page 235... ...
Data Transmission Facilities The first electrical telecommunication system transmitted a digital signal the Morse code of telegraphy. Today, although some communication facilities are limited to telegraph data transmission rates fire alarm and traffic light control networks, for example the vast bulk of communication channels are designed to transmit voice signals.
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From page 236... ...
A level 3 channel could either carry 672 voice channels or a properly encoded entertainment-grade television signal. Because the assignment of the meaning of the bits in any channel is arbitrary, these transparent channels of the communications infrastructure can be the components of a telematics infrastructure provided a protocol to define the meaning of a stream of bits has been established.
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From page 237... ...
In addition to its speed advantage, packet switching is far superior to circuit switching for transmitting messages to multiple receivers; with a change of address at the head end of the packet, messages can be sent simultaneously to many locations. Terminals Terminals on a telematics network are referred to as "smart" or "dumb," depending on whether they have internal data processing capabilities; a microcomputer thus is a smart terminal, and a teletypewriter is dumb.
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From page 238... ...
Parallel processing, a common term in contemporary computer design, refers more directly to the use of multiple processing units within a computer than to the use of distributed processing. Development of strategies and programming tools for efficient parallel processing is a formidable task expected to lead to new levels of processing speed.
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From page 239... ...
Occasionally, a private standard becomes a de facto industrywide standard, either because the initiating entity dominates the industry, as AT&T did for its telephone network plan, or because it is more convenient to adopt an existing standard than to develop a new one, as some other suppliers found in the case of Xerox's Ethernet. When a system is not the sole responsibility of a single supplier, a forum for agreement among the many suppliers must be established.
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From page 240... ...
The lowest three levels are primarily concerned with data communications, and the upper three with the software issues unique to telematics. The intermediate fourth level involves data processing that helps control communications.5 ARRANGEMENT OF TELEMATICS SYSTEMS Topologies and Data Flows Data transmission channels have directionality.
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From page 241... ...
They use either circuit or packet switches, but they assign channels and times of transmission uniquely according to internal protocols and the addresses presented. The compound arrangement is characteristic of the public switched telephone network, which uses full channels, and nationwide packet-switched networks, which use simplex channels.
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From page 242... ...
are, as the name implies, data networks that serve a small area, such as a university campus or an industrial park. A star topology entered through telephone lines in a local private branch exchange may be used if data rates are low and the efficiency of packet switching is not needed.
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From page 243... ...
Computer Intrusion Tapping a telephone line to listen to people talking has been a federal offense for years, and in the fall of 1986 it became a federal offense to tap a data stream. Although there are state laws, as in California, that prohibit the unauthorized use of a computer, there are also federal sanctions for an electronic intruder in, for example, Arizona who readjusts financial accounts in a California bank.
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From page 244... ...
With the removal of AT&T as the proprietor of the bulk of the national telecommunications network, two changes in the evolution of telematics have occurred: AT&T can no longer set de facto protocols and standards for the nation, and the regulatory pressure to keep depreciation rates low has evaporated. The result of the first change is that revision of standards and protocols will be slowed by the need to have competitors agree, although, as discussed earlier in this chapter, there are already forums for such deliberations.
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From page 245... ...
Its use is a political issue because regulators are concerned that the loss of the profits from overpriced business telecommunication services will force local telephone companies to raise the price of residential services
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From page 246... ...
Social Issues The social issues accompanying the introduction of telematics are being addressed by appropriate legislative, institutional, and business groups. Opportunities for damage by computer intrusion should decrease as new laws are passed and as data base managers introduce access controls and tighten security.
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From page 247... ...
Although data signals at a few hundred bits per second will pass easily through a relay connection network, the logic in relay control systems is simple and inflexible and not adaptable to the more exotic demands of some data communications. Electronic switching was introduced in the early 1960s when relays were used for connections, but the control function was a special-purpose, stored-program computer that could accommodate complex logic and software changes.
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From page 248... ...
The control function in such switches is, again, a computer controlled by a stored program, but connections are made in a totally different fashion. Input and output channels are time slots in a time division carrier system.
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