
B–63833EN–1/02
17. PCMCIA ETHERNET FUNCTION
981
This section briefly describes Ethernet–related terms.
The descriptions below provide minimum information only. For further
information, refer to relevant publications available on the market.
For Ethernet–based communication, the TCP/IP (Transmission Control
Protocol/Internet Protocol) protocol is generally used. A protocol is a set
of rules used to ensure smooth communication between communication
devices connected via a transmission line. The TCP/IP protocol is a part
of the hierarchical structure consisting of the protocols and services
indicated below.
Hierarchy Protocol/network service
Application layer User services such as FTP
Transport layer Protocols such as TCP and UDP
Network layer Protocols such as IP and ICMP
Data link layer
MAC layer
Protocols such as ARP and RARP
Physical layer Hardware such as cables and devices
In general, the TCP/IP protocol is a generic term that represents the
protocols installed in the transport layer and network layer.
With TCP/IP, an address referred to as an IP address (INET address) is
used to identify a specified communication device among the
communication devices connected via Ethernet. So, for communication
using TCP/IP, each communication device connected to Ethernet must
have a unique IP address assigned.
An IP address is four octets (bytes) long. Usually, an IP address is
represented by four 8–bit (octet or byte) fields separated by a period from
each other. Each octet can have a value from 0 to 255.
An IP address consists of the address of the network to which the
communication device is connected, and the host address of the
communication device. Networks are classified into three classes by
group size: class A, class B, and class C.
First octet value Network
address section
Host address
section
Class A 0 to 127 xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx
Class B 128 to 191 xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx
Class C 192 to 223 xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx
(A hatched portion indicates the section of each address.)
If a network supports no more than 255 communication devices, class C
is generally used.
The IP addresses of all communication devices on one network have the
same network address, and only the host address of each communication
device is unique on the network.
An IP address with its network address and host address all set to 0 or 255
is unusable.
17.7
GLOSSARY FOR
ETHERNET
TCP/IP
IP address (INET
address)