Page 86 - Intelligent Communication Systems

CHAPTER 7/NEWLY DEVELOPED TELECOMMUNICATION SERVICES 69
the same instant. If messages are transmitted through the bus at the same time and
a conflict occurs, then the source waits a moment and then issues the message
again. When the message is reissued it is determined by, for example, using a table of
random numbers. This method is similar to a roundtable discussion, where some-
one begins to talk and other people wait until the first speaker finishes before they
talk. When more than one person begins to talk at the same time (a conflict), one
speaker stops talking and waits until the other finishes. In this way the discussion
can continue.

7.7.2.2 Token Ring
In this method, a token goes around the ring circuit. Terminals are accommodated
on the ring. When a terminal is ready to send a message to another terminal, it
catches the token, places a message with a destination ID in the token, and then re-
leases the token on the ring circuit. The destination terminal catches the token,
reads the message, writes an acknowledgment on the token, and releases it on the
ring circuit. In this way, message passing can be performed smoothly and without
conflict.

7.8 CONTINUOUS ACQUISITION AND LIFELONG SUPPORT

Although continuous acquisition and lifelong support has been acronymed CALS,
more recently CALS has come to mean "commerce at light speed"; that is, CALS
provides the means, tools, or systems for conducting business transactions at light
speed. In the business world, there are a variety of documents, such as a written
order, a document for maintenance, and/or a document for sales. Each has a dif-
ferent form. It is therefore necessary to access each one separately if we want to
know specific information. This takes time. Generally speaking, documents have
different styles, are written in different languages, and are made by different pro-
cessors. The number of documents has been increasing year by year. To reduce the
number of documents and to access the information efficiently, CALS was pro-
posed. In this system, written orders or documents for maintenance or sales are
integrated into a single document, and all of the information can be accessed by
reading the integrated document. In CALS, the style of the document is standard-
ized, and it can be used during the life cycle of goods, namely, order, development,
sales, and maintenance.

7.8.1 Features of CALS
(1) The document is digitized, enabling efficient processing.
(2) The document is standardized; that is, the style and the form are defined.
(3) CALS is an open system and runs on any kinds of hardware or operating
systems. Thus it enables data interchange to be performed efficiently and effectively.