The TCP/IP model
TCP/IP is based on a four-layer reference model. All protocols that belong to the TCP/IP protocol suite are located in the top three layers of this model.
As shown in the following illustration, each layer of the TCP/IP model corresponds to one or more layers of the seven-layer Open Systems Interconnection (OSI) reference model proposed by the International Standards Organization (ISO).
The types of services performed and protocols used at each layer within the TCP/IP model are described in more detail in the following table.
|Application||Defines TCP/IP application protocols and how host programs interface with transport layer services to use the network.||HTTP, Telnet, FTP, TFTP, SNMP, DNS, SMTP, X Windows, other application protocols|
|Transport||Provides communication session management between host computers. Defines the level of service and status of the connection used when transporting data.||TCP, UDP, RTP|
|Internet||Packages data into IP datagrams, which contain source and destination address information that is used to forward the datagrams between hosts and across networks. Performs routing of IP datagrams.||IP, ICMP, ARP, RARP|
|Network interface||Specifies details of how data is physically sent through the network, including how bits are electrically signaled by hardware devices that interface directly with a network medium, such as coaxial cable, optical fiber, or twisted-pair copper wire.||Ethernet, Token Ring, FDDI, X.25, Frame Relay, RS-232, v.35|