The TCP/IP protocol suite is so named for two of its most important protocols:
Transmission Control Protocol (TCP) and Internet Protocol (IP). A less used name for it is the Internet Protocol Suite, which is the phrase used in official Internet standards documents. We use the more common, shorter term, TCP/IP, to refer to the entire protocol suite.

The main design goal of TCP/IP was to build an interconnection of networks, referred to as an internetwork, or internet, that provided universal communication services over heterogeneous physical networks. The clear benefit of such an internetwork is the enabling of communication between hosts on different networks, perhaps separated by a large geographical area.

The words internetwork and internet are simply a contraction of the phrase interconnected network. However, when written with a capital "I", the Internet refers to the world-wide set of interconnected networks. Hence, the Internet is an internet, but the reverse does not apply. The Internet is sometimes called the connected Internet.
The Internet consists of the following groups of networks:

• Backbones: Large networks that exist primarily to interconnect other networks. Currently the backbones are NSFNET in the US, EBONE in Europe, and large commercial backbones.
• Regional networks connecting, for example, universities and colleges.
• Commercial networks providing access to the backbones to subscribers, and networks owned by commercial organisations for internal use that also have connections to the Internet.
• Local networks, such as campus-wide university networks.

Figure 1 shows two examples of internets. Each is composed of two or more physical networks.

Another important aspect of TCP/IP internetworking is the creation of a standardised abstraction of the communication mechanisms provided by each type of network. Each physical network has its own technology-dependent communication interface, in the form of a programming interface that provides basic communication functions (primitives). TCP/IP provides communication services that run between the programming interface of a physical network and user applications.
It enables a common interface for these applications, independent of the underlying physical network. The architecture of the physical network is therefore hidden from the user and from the developer of the application. The applications need only code to the standardised communication abstraction to be able to function under any type of physical network and operating platform.

As is evident in Figure 1, to be able to interconnect two networks, we need a computer that is attached to both networks and can forward data packets from one network to the other; such a machine is called a router. The term IP router is also used because the routing function is part of the Internet Protocol portion of the TCP/IP protocol suite (see The TCP/IP protocol layers).

Like most networking software, TCP/IP is modelled in layers. This layered representation leads to the term protocol stack, which refers to the stack of layers in the protocol suite. It can be used for positioning (but not for functionally comparing) the TCP/IP protocol suite against others, such as Systems Network Architecture (SNA) and the Open System Interconnection (OSI) model.

To be able to identify a host within the internetwork, each host is assigned an address, called the IP address. When a host has multiple network adapters (interfaces), such as with a router, each interface has a unique IP address.

TCP/IP, as an internetwork protocol suite, can operate over a vast number of physical networks. The most common and widely used of these protocols is, of course, Ethernet.

• Proxies
• TCP/IP Routing Tables
• There are many ways to provide access to other networks. In an internetwork, this done with routers. It is necessary to distinguish between a router, a bridge and a gateway for allowing remote network access.
  • Bridges
  • Routers
  • Gateways