Appendix A
GLOSSARY
User of this manual should be familiar with following definitions:
ARP (Address Resolution Protocol)
is a protocol for mapping an Internet Protocol address
(IP address) to a physical machine address that is recognized in the local network. For
example, the IP address in use today is an address that is 32-bits long.
In an Ethernet
local area network, however, addresses for attached devices are 48-bits long. (The physical
machine address is also known as a Media Access Control or MAC address.) A table, usually
called the ARP cache, is used to maintain a correlation between each MAC address and its
corresponding IP address. ARP provides the protocol rules for making this correlation and
providing address conversion in both directions.
Ethernet
is a network protocol defined by the IEEE 802.3 standard. Ethernet-based
networks use MAC Address rather then IP Address to exchange data between computers. By
using ARP and adding TCP/IP support, Ethernet devices may be connected as part of the
Internet. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires.
The most commonly installed Ethernet systems are called 10BASE-T and provide
transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for
access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.
IP (Internet Protocol)
is the method or protocol by which data is sent from one computer to
another on the Internet.
IP address (Internet Protocol address)
is a 32-bit number that identifies each sender or
receiver of information that is sent in packets across the Internet.
IP Netmask
is a 32-bit pattern of bits used to determine which part of the IP address is the
network portion and which part is the host portion.
MAC (Media Access Control) Address
is your computer's unique hardware number. When
you're connected to the Internet from your computer, a correspondence table relates your IP
address to your computer's physical (MAC) address on the LAN.
Ping
is a utility that tests the network connectivity. It is used to determine if the host is
capable of exchanging information with another host.
Port number/Socket number
is a way to identify a specific process to which an Internet or
other network message is to be forwarded when it arrives at a server. It is a predefined
address that serves as a route from the application to the Transport layer or from the
Transport layer to the application of the TCP/IP system.
Sockets
are a method for communication between a client program and a server program in
a network and defined as "the endpoint in a connection." Information transferred across the
Internet primarily occurs between sockets.
SMTP
Simple Mail Transfer Protocol is an Internet standard for electronic mail (email) transfer
across the Internet. SMTP clients usually use SMTP to send email messages by specifying
the SMTP server. The email server uses SMTP to both send and receive email messages.
SNMP
Simple Network Management Protocol is a network monitoring protocol to monitor
devices connected to an Ethernet Network.
TCP/IP (Transmission Control Protocol/Internet Protocol)
is the basic communication
language or protocol of the Internet. When you are set up with direct access to the Internet,
your computer is provided with a copy of the TCP/IP program just as every other computer
that you may send messages to or get information from also has a copy of TCP/IP. TCP/IP
often is used as a general term to indicate generic access to the Internet.
Terminating Resistor
is a resistor placed at the extreme end or ends of the RS485 serial
cable (across the -Tx/Rx and +Tx/Rx). On one end where the iServer is connected a 120-ohm
terminating resistor is built in internally therefore there is no need for termination. However, on
the end where the RS485 device is connected, if the device does not have an internal
terminating resistor you should connect a 120-ohm resistor across the -Tx/Rx and +Tx/Rx
wires (see
Wiring RS485 Interface Section
). Lack of termination can cause data corruption
due to electrical noise sensitivity. The value of the terminating resistor is ideally the same
value as the characteristic impedance of the cable (typically, 120 ohms for twisted pairs).
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