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2-15-2 Description of terminology
■ TCP/IP (Transmission Control Protocol/Internet Protocol)
TCP/IP is a general term for a group of standard protocols for carrying out communications over
the Internet centering around TCP and IP protocols. Computers and PCs capable of accessing the
Internet all use TCP/IP protocols.
The Ethernet unit for RCX series contains TCP, IP, ICMP, ARP and TELNET protocols among
TCP/IP protocols.
TCP
TELNET
■ Ethernet
The Ethernet is basically one type of standard for network system hardware. Ethernet is a network
invented by the Xerox Corporation (USA) in the early 1970's and currently forms an international
standard known as IEE802.3. The Ethernet physically consists of cable types such as 10BASE-2,
10BASE-5, and 10BASE-T that differ from each other in terms of transmission cable types such
as maximum cable length and the maximum number of connections. The Ethernet unit for RCX
series uses cables conforming to 10BASE-T specifications.
Besides TCP/IP, the protocols most commonly used on the Internet are NetBEUI and IPX/SPX,
etc.
Another feature of the Ethernet is the use of CSMA/CD as a data transmission method.
(see below).
■ CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
CSMA/CD is a method of sending signals, developed by combining a CSMA data transmission
method with a transmission error handling method called CD.
CSMA refers to joint use of one transmission cable by many devices connected over a network.
CSMA is therefore a method for checking network status beforehand and then transmitting the
data after verifying that transmission is possible.
CD is a method for handling data collisions that occur on the network. In this method, when a data
collision (conflict) occurs, that data is re-transmitted after a randomly selected time period has
elapsed.
Many devices can be connected to the Ethernet by using these CSMA/CD methods. However,
performance cannot be guaranteed in real-time because of transmission standby (time awaiting
transmission) and retransmissions.
IP
ARP
UDP
ICMP
FTP
HTTP
TCP/IP protocols
2-15 Supplement
The protocols making up
*
TCP/IP are also comprised
of many protocols other than
those shown in the figure on
the left. Protocols are a set
of conventions (or rules) that
must be mutually complied
with so that controllers and
PCs can communicate with
the other party.
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