Definition of TCP/IP in The Network Encyclopedia. The most widely used communication protocol.

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What is TCP/IP?

An abbreviation for Transmission Control Protocol/Internet Protocol, an industry-standard protocol suite for wide area networks (WANs) developed in the 1970s and 1980s by the U.S. Department of Defense (DoD). TCP/IP is a routable protocol that is suitable for connecting dissimilar systems (such as Microsoft Windows and UNIX) in heterogeneous networks, and it is the protocol of the worldwide network known as the Internet. Microsoft’s implementation of TCP/IP supports industry standards, and TCP/IP is implemented for all Windows operating systems.

Graphic T-4. TCP/IP.

How TCP/IP Works

The architecture of the TCP/IP protocol suite has four layers that map loosely to the seven-layer Open Systems Interconnection (OSI) reference model (as shown in the diagram). The TCP/IP model is sometimes called the DoD model because TCP/IP was developed in connection with the ARPANET project of the U.S. Department of Defense. Each layer of the TCP/IP protocol suite has its associated component protocols, the most important of which are listed here:

TCP/IP uses two naming schemes to identify hosts and networks on an internetwork:

  • IP addresses:
    Logical 32-bit (4-byte) numeric addresses of the form w.x.y.z. They are partitioned (using a subnet mask) into two segments, a network ID and a host ID. For example, the IP address is partitioned using the subnet mask into the network ID and the host ID 44. IP addresses are the basic or primary way of identifying hosts and networks on an internetwork; they can be assigned to computers manually or by using DHCP.


  • Fully qualified domain names (FQDNs):
    Alphanumeric names of the form host_name.domain_name in which domain_name is part of DNS, a hierarchical worldwide naming system. For example, the FQDN represents a host named server12 that belongs to a network whose domain name is microsoft, which belongs to the top-level domain named .com, which belongs to the root DNS domain named dot. FQDNs are friendly names. They are easier to remember than IP addresses and are resolved into IP addresses by using a DNS server or a local hosts file.



TCP/IP is a constantly evolving protocol suite whose development is steered by such bodies as the Internet Society (ISOC), the Internet Architecture Board (IAB), and the Internet Engineering Task Force (IETF). The current version of TCP/IP is called IPv4 (Internet Protocol version 4); a new version called IPv6 is under development.

To learn more about TCP/IP get The Illustrated Network, Second Edition: How TCP/IP Works in a Modern Network from Amazon.