Page 257 - Sensors and Control Systems in Manufacturing

Networking of Sensors and Contr ol Systems in Manufacturing
Several versions of MAP have been developed. One difficulty of 217
several has been obtaining agreement among many different coun-
tries and vendor groups on a specific standard. Another problem is
that the resulting standards are so broad they have become very com-
plex, making it difficult to develop the hardware and software to
implement the system and consequently driving up related costs. The
early version of MAP addressed some of the OSI layers to a limited
degree, and made provision for users to individualize the application
layer for a particular use. The latest version of MAP makes an effort
to define more completely all the application layer software support
as well as the other layers. This has led to continuing disagreements
and struggles to produce a protocol that can be adopted by every
vendor group in every country to achieve MAP goals.
Because of its complexity, MAP compatibility among equipment
units, or interoperability, has been a continuing difficulty. MAP has
not been applied as rapidly as was initially hoped for by its propo-
nents because of the complexity, costs, and disagreements on how it
should be implemented. Assembling a complete set of documenta-
tion for MAP is a difficult activity that requires compiling a file of
standards organization reports, a number of industry organization
reports, and documentation from all the working committees associ-
ated with ISO.

4.10.1 Broadband System for MAP Protocol
The MAP protocol was developed with several alternatives for phys-
ical layer (PhL)1. It can be implemented through what is called a
broadband system (Fig. 4.13), and so manufacturing units can talk to
one another, transmitted messages are placed on the cable—a head-
end remodulator then retransmits these messages and directs them to
the receiving station. The broadband version of MAP has the highest
capabilities because it allows several types of communications to take
place on the same cabling at the same time. On the other hand,
because of its greater flexibility, a broadband system is more complex
and more expensive to install. It requires modems and MAP interface
equipment for each item of equipment and a head-end remodulator
to serve the entire network. The main cable used for broadband is
unwieldy (approximately 25 mm in diameter) and is appropriate
only for wiring very large factories. Multiple drop cables can be
branched off the main cable for the different MAP nodes. Broadband
communication can achieve a high data rate of 10 Mb/s and can split
the frequency spectrum to allow several different communications to
take place simultaneously. As indicated in Fig. 4.14, the three transmit
frequencies and the three receive frequencies are separated from one
another in the frequency domain. Three different channels can coexist
on the MAP network. The headend remodulator transfers messages
from the low frequencies to the high frequencies.