Description of terminology, TCP/IP protocols Ethernet

CHAPTER2 Ethernet Unit

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 communi- cations 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 contains TCP, IP, ICMP, ARP and TELNET protocols.

	TCP	IP
	TCP	ARP
	TELNET	UDP
	TELNET	ICMP
		ICMP
	HTTP	FTP

TCP/IP protocols

■Ethernet

*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.

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 cur- rently 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 maximum cable length and the maximum number of connections. The Ethernet unit 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.