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The TCP/IP model

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

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).

OSI layer model and TCP/IP model

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.

Layer Description Protocols


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


Provides communication session management between host computers. Defines the level of service and status of the connection used when transporting data.



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.


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

For more information about ARP, IP, ICMP, IGMP, UDP, and TCP, see Understanding TCP/IP.


  • The OSI reference model is not specific to TCP/IP. It was developed by the ISO in the late 1970s as a framework for describing all functions required of an open interconnected network. It is a widely known and accepted reference model in the data communications field and is used here only for comparison purposes.