As mentioned earlier, TCP/IP is the most widely used protocol suite. The relationship between the five layers of the TCP/IP protocol suite and the seven layers of the OSI model is illustrated in Figure 1-4.
Figure 1-4 TCP/IP Protocol Suite
Transport Internet Data Link
The five layers of the TCP/IP suite are the application layer, transport layer, Internet layer, data link layer, and physical layer.
NOTE The data link and physical layers are sometimes grouped as one layer, called the network interface layer.
The TCP/IP application layer includes the functionality of the OSI application, presentation, and session layers. Applications defined in the TCP/IP suite include the following:
■ FTP and Trivial File Transfer Protocol (TFTP): Transfer files between devices.
■ SMTP and POP3: Provide e-mail services.
Physical OSI Model
■ HTTP: Transfers information to and from a World Wide Web server through web browser software.
■ Telnet: Emulates a terminal to connect to devices.
■ Domain Name System (DNS): Translates network device names into network addresses and vice versa.
■ Simple Network Management Protocol (SNMP): Used for network management, including setting threshold values and reporting network errors.
■ Dynamic Host Configuration Protocol (DHCP): Assigns dynamic IP addressing information to devices as they require it.
The transport layer and Internet layer protocols are detailed in the following sections.
The data link and physical layers can support a wide variety of LANs and WANs (including those discussed in the "LANs and WANs" section, earlier in this chapter). A data link layer protocol related to the TCP/IP suite is described in the later "TCP/IP-Related Data Link Layer Protocol"
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