Page 38 - Intelligent Communication Systems

22 INTELLIGENT COMMUNICATION SYSTEMS
the Domain Name Service (DNS), Telecommunication Network Protocol (TELNET),
and File Transfer Protocol (FTP), SMTP is the protocol that provides message
transfer functions between computers. It is used for electronic mail and bulletin
board services, DNS provides the service that translates a domain name to the IP
address. TELNET is the protocol that establishes the TCP connection between a
user's computer and a remote peer computer. Through this, he or she can issue a
remote login and access the remote computer. FTP is the protocol that provides
the file transfer between computers. Using FTP, a user can log onto a remote com-
puter, access the directory of the file, and copy the contents of the file. The con-
nection is established by TELNET before FTP is used. In this layer, are the Trivial
FTP (TFTP) as the simple file transfer protocol and the Network Voice Protocol
(NVP) as the protocol for voice transmission.
In the transfer layer is the Transport Control Protocol (TCP), which enables
connection-type communication between two nodes. It corresponds to the virtual cir-
cuit on a packet switching system and is a typical protocol on the Internet. The User
Datagram Protocol (UDP) provides connectionless-type communication and cor-
responds to the datagram communication in the packet switching network.
Table 3.1 shows the dependence among the subprotocols, both in the applica-
tion layer and in the transport layer. For example FTP and TELNET use TCP, and
TFTP uses UDP.
In the Internet layer, IP is the fundamental protocol. It provides a connec-
tionless-type data transmission function between a node and its peer node via a
number of communication networks. IP specifies the format of the IP datagram,
how to perform a routing, and how to correct errors. The Internet Control Message
Protocol (ICMP) is the protocol that transmits the control information concerning
the monitoring of communication networks or gateways between a node computer
and its peer computer. The Address Resolution Protocol (ARP) or the Remote ARP
(RARP) is the protocol that translates an IP address to its physical address on the
Ethernet, and vice versa if needed.
Both the network interface layer and the physical layer specify the communi-
cation networks for data transmission, such as the Ethernet, ARPA network, and
X.25 packet switching network, and the interface.