User Manual Part 2

CHAPTER 7
THEORY OF OPERATION
Revised: 9 Oct 03 7-1 EST P/N AA104
INTRODUCTION
ESTeem wireless modem products provide a "Wireless Solution" by eliminating conventional hardwiring of leased phone lines.
All of the ESTeem models come with the industry standard RS-232C, RS-422, and RS-485 asynchronous communications ports
to give the user a new dimension to "Local Area Networking".
Our packet burst, frequency agile communications products allow the user to create a "Radio Area Network" of up to 255 users
on a single frequency. The packet burst communications technique was chosen to give the system very high data integrity in
high noise industrial environments. The ESTeem incorporates a method of error checking that provides received data accuracy
of greater than one part in 100 million.
Internal Digi-Repeater features allow the user to increase operating range by relaying transmission through a maximum of three
ESTeems to reach the destination ESTeem. An ESTeem can operate as an operating node, a repeater node, or both
simultaneously for added flexibility.
"Private Data Communications" is provided by the use of an interleaving technique of the modulated data, user definable
commands for unit addressing, network addressing, and security lock-out of software programming. If higher security is
required, the ESTeem is compatible with asynchronous Data Encryption Standard (DES) encryption devices.
The ESTeem has programmable software commands to allow the user to easily configure the unit for any application or mission.
The ESTeem setup parameters are saved in non-volatile memory.
When you buy ESTeem products you are getting equipment designed by the company that holds the United States and
Canadian patent for the wireless modem. We are proud to say that we design, develop and manufacture our products in the
United States. Each ESTeem is subjected to a rigorous quality control bench test before shipping to insure our customers have
out-of-the-package reliability. We also have a dedicated Customer Support Staff, Field Engineering Services and Factory
Training classes to make sure that your application problems are solved.
HOW IT WORKS
Now, as you can probably guess, the ESTeem is a sophisticated piece of technology, however the concept is easy to
comprehend if you understand packet radio.
All packet systems, whether hardwired or radio, share the same principle of operation; data is taken from your standard RS-232C,
RS-422, or RS-485 asynchronous port and is transmitted in "Blocks". Think of this block as an "Electronic Envelope" that we
call a packet. The size of the packet can be defined by the user from 1 to 2000 bytes of information. Reducing the size of the
packet allows the ESTeem to operate better in high EMF noise environments, because by reducing the packet size you reduce
transmission exposure time on the radio waves thereby increasing your probability of a successful transmission.
Once this packet of data is formed, it’s transmitted in a "burst," one ESTeem to another, hence the term "packet burst
communications". Now, if more than one packet is required to send the data then the ESTeem goes into full automatic mode and
transmits additional packets.
Before an ESTeem transmits its packet it listens to ensure that the air waves are clear before transmitting. This listen before
transmit scheme is called "carrier sensed multiple access," or CSMA.
When a "packet" has been transmitted, every modem in radio range on the same frequency hears it. To design a modem to
communicate with a network of modems it has to be "address specific" so only the modem you want to talk to accepts your
information. It's like yelling into a crowd of 255 people but you want only the person’s name you called to acknowledge (ACK).