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Accessibility 1998 |
| Seminars | Resources | About | |
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Seminar on Accessibility for All : Presentations : Internet Information Technologiesby
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| Slides | Notes: |
Slide 1:Accessibility 1998Internet information policies, structures and technologies |
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Slide 2:The challenge for international organizations
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The Internet is a challenge for international organizations, both public and not-for profit. To deal with this challenge in terms of accessibility, you have to begin with an understanding of the telecommunications explosion, the underlying technologies and their policy implications. This session looks at these aspects. |
Slide 3:The digital revolution
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The need to calculate trajectories for artillery led to the quest for methods of computation more efficient than rooms full of clerks performing calculus and arithmetic with paper and pencil. Mechanical calculators such as the famous Friden calculator were used during World War I by the ballistics and ordnance engineers of all combatants. During World War I, banks of inter-linked electro-mechanical relays and, later, vacuum tubes were used to create computing machines of great, for the time, mathematical power and speed. The machines were large, expensive, power hungry and high maintenance. Business, entertainment, education and communications uses for the giant machines were not in the minds of the creators. |
Slide 4:The language of computers
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People in the digital trades like to say that
everything can be reduced to zeroes and ones. That is wrong, of course.
Pictures, sounds, words and numbers, however, can be coded as a series of
binary digits (0 or 1) and assembled into groups called bytes,
conventionally 8 bits long.
The great virtue of digital encoding is that, with a little care, content can be reproduced endlessly without change or loss. The transistor is a very small switching device with two states, on and off that can be used to represent the binary encoding of content. First dozens,then hundreds, thousands and millions of transistors can be etched onto tiny ceramic chips which can themselves be reproduced endlessly and cheaply. |
Slide 5:From mainframes to microcomputers and back again
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Slide 6:From couriers to fiber optic: a one-minute history
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Communications technology combined with
computers is the foundation of the technology revolution we are living
through today. The oldest form of long distance communication was the hand
carrying of clay tablets, scrolls, journals and books by couriers with and
without mounts. The first mechanized long distance communication system was
put into production by the Scandinavians and the French around the time of
Napoleon: a series of manned towers, spaced a few kilometers apart which
relayed coded messages by arranging signal flags to signify letters and
words. Today we would describe the transmission speed as 60 bytes per hour.
The telegraph and telephone, of course, speeded things up by factors of
hundreds; a good railroad telegrapher could click out 100 words a minute. The newest forms of communication are phone and data delivery by means of multiple overlapping radio transmitters and receivers arranged geographically into small areas called cells. PCS, short for personal communications system, is the same thing under a different name. Television, or more broadly, video can be used not only for one-way communication to a passive recipient but can also be used for active two-way communication. |
Slide 7:Convergence: Communications and computers
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As chips have decrease in size and cost, they
have been dispersed into the communications networks. In the early days of computing, say the 1950’s, computers had to be operated directly through devices such as Hollerith punch cards and only one person at a time could use the machine. With the development of time-sharing computer operating systems many people could use the machine simultaneously ( or so it would seem for all practical purposes). If time-sharing users were distant from the central computer, a device called a modem converted the digital signals into electrical signals compatible with the voice telephone system. The process is reversed at the computer end. New interconnection methods eliminate the modem intermediaries. ISDN interfaces, local area networking and digital subscriber lines (DSL) of various kinds keep the signals digital along the entire path. |
Slide 8:Networks in a new mode
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All digital networks are destined to replace
the analog phone network. Instead of reserving an entire circuit for the
duration of a session to one purpose, digital networks highly efficiently
mix traffic from many sources over the same circuit and still mange to
deliver content to the right destination.
Networks that do not reserve an entire path to one user at a time are called unswitched; a good example is an Ethernet lan. |
Slide 9:The shift from voice to dataProjected Shift in US Marget Growth The Data Market is growing 24% faster than the Voice Market. By the year 2000 Data will exceed Voice by 44%. |
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Slide 10:The international digital heirarchy
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This chart is one way of keeping track of how
fast is fast when twlking about data speeds. The basic unit of digital
speed, the “meter” as it were, is the DS-0 at 64 thousand bits per second.
It is a convenient number in digital arithmetic and is sufficient to carry
the human voice in digital form with adequate quality. DS-1 and E-1 speeds are widely available for use by high volume users such as internet service providers. The speeds from OC-3 (which stands for Optical Carrier level 3) on up are now used for backbone, behind-the-scenes networking, but we can expect them to become more commonly available for end-users in the next couple of years. |
Slide 11:From the desktop to the world
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Local Area Networks (LANs) can be very large
but are topographically limited to a small area which can be physically
connected with private facilities. Factories, office buildings, campuses and
homes are typical LAN sites. For dispersed enterprises, a Metropolitan Area Network (MAN), will typically purchase services from a local telephone company to link several LANs. Cost becomes more of a factor is determining the right mix of methodologies and equipment. Wide Area Networks can link LANs and MANs around the globe. Cost and configuration become critical. The Internet is the ultimate WAN. |
Slide 12:Local area networks
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The first round of local area networks were
designed when communications links and computing power were both expensive.
It made sense to concentrate the computing on one big machine and to link
quantities of terminals to the central machine through intermediate
communication controllers. The IBM 3270 family of terminals and controllers
typified this hub and spoke approach; there are still many systems of this
kind in use.
Local networks based on the notion of every device having an equal chance of access to the communication line are called token ring networks. Ethernet takes a different approach: each device on the net determines whether the communications line is available at the instant before sending a message to another device. Ethernets operate at line speeds up to 100 million bits per second; engineers are working on still higher speeds. The data on an Ethernet is assembled into groups of bits called packets which contain not only the message content but also the senders address, the recipients address, unique serial numbers, error-correcting codes and more. X.25 and Frame Relay are two forms of networks explicitly based on packet concepts. Asynchronous Transfer Mode, ATM for short, is similar but distinct. All groupings of bits are exactly the same length, which makes for ease in handling at the device level, and the groupings (or cells) additionally identify the kind of data: voice, video or pure data. |
Slide 13:MANS and WANS
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A MAN is a Metropolitan Area Network. We will
make no jokes at this point, however we might be tempted. A WAN is a Wide
Area Network. Since MANs and WANs almost always have to use publicly
available commercial facilities, standards for interconnecting become vital.
Threee of the most important are these. ISDN is a set of International Telecommunications standards for digital communications. It has been widely deployed in the public switched telephone network at the switch to switch level but has not won very many adherents among consumers. SONET and SDH are another set of international standards specifically
designed for the very high speeds which fiber optics make possible. The
optical standards don’t dictate a particular networking technology. Think of
them as the superhighways on which all sorts of vehicles can travel. |
Slide 14:Technology EvolutionBandwidth Growth
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Slide 15:The computer is the network
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The rapidly decreasing cost of computation has enable d the actual processing of information to be spread throughout the networks to the point where it makes sense to say the network is the computer. Access to processing of all things digital has been democratized and decentralized. The question before social thinkers is what effect this will have on the development of social life and whether there are ways to channel the communications and computer revolution to more beneficent ends. |
Slide 16:The media for the messages
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It is important to understand that the physical media that carry digital information are neutral. They each have characteristics absolutely dictated by physics but each are capable of carrying digital signals convertible into sound, images and numbers. |
Slide 17:The Internet and the World Wide Web
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