onboard networks 191COMPUTER AND NETWORKING TERMINOLOGY
In this discussion of networks, we will be entering what may be for some a new realm of specialized
knowledge. To assist you, here are definitions for some of the terms used in this book:
bandwidth:A range within a band of frequencies or wavelengths. Also, the amount of data that can
be transmitted in a fixed amount of time; the data rate supported by a network connection or interface.
Commonly expressed in bits per second (bps).
baseband:The original band of frequencies of a signal before it is modulated for transmission at a
higher frequency. Typically used to refer to the digital side of a circuit when the other side is
broadband or frequency based, meaning the signal is modulated. For example, in a cell phone, “RF
to baseband” means pulling out the analog or digital data from the modulated RF signal received
from the cell phone tower and converting it to pulses for digital processing.
black box:A sealed, unserviceable electronic control box that serves various functions within an elec-
tronic or networked system.
broadband: In general, broadband refers to telecommunication in which a wide band of
frequencies is available to transmit information.
CAN (controller area network):A serial bus network of microcontrollers that connects devices, sen-
sors, and actuators in a system or subsystem for real-time control applications. There is no addressing
scheme used, as in the sense of conventional addressing in networks (such as Ethernet). Rather,
messages are broadcast to all the nodes in the network using an identifier unique to the network.
Based on the identifier, the individual nodes decide whether or not to process the message and also
determine the priority of the message in terms of competition for bus access. This method allows for
uninterrupted transmission when a collision is detected, unlike Ethernets that will stop transmission upon
collision detection. Controller area networks can be used as an embedded communication system for
microcontrollers as well as an open communication system for intelligent devices.
Ethernet:Originally developed by Xerox in 1976, it now describes a diverse family of frame-based
computer networking technologies for local area networks (LANs). It is the basis for IEEE standard
802.3. (If you want to learn more about Ethernet protocol, the Internet is absolutely loaded with sites
that will walk you through the various protocols and the cryptic codes that identify them.)
multiplexer:A communications device (black box) that combines several signals for transmission over
a single medium.
network:A group of two or more computer systems linked together to share information and
hardware.
network architecture:The structure of a communications network. An open architectureallows adding,
upgrading, and swapping of components. It can be connected easily to devices and programs made
by other manufacturers. It uses off-the-shelf components and conforms to approved standards. A
closed architecturehas a proprietary design, making it difficult to connect the system to other systems.
The hardware manufacturer chooses the components, and they are generally not upgradable.
protocol:In the context of data communication, a common set of rules, signals, and data structures
(for either hardware or software) that governs how computers and other network devices exchange
information over a network.
sentence structure:In NMEA parlance, describes the sequence and type of data information codes that
are distributed throughout the network. (For specific sentence codes, see the sidebar on page 151.)