Internetworking involves connecting two or more computer networks via gateways using a common routing technology. The result is called an internetwork (often shortened to internet).
The most notable example of internetworking is the Internet (capitalized), a network of networks based on many underlying hardware technologies, but unified by an internetworking protocol standard, the Internet Protocol Suite (TCP/IP).
The network elements used to connect individual networks are known as routers, but were originally called gateways, a term that was deprecated in this context, due to confusion with functionally different devices using the same name.
The interconnection of networks with bridges (link layer devices) is sometimes incorrectly termed “internetworking”, but the resulting system is simply a larger, single subnetwork, and no internetworking protocol (such as IP) is required to traverse it. However, a single computer network may be converted into an internetwork by dividing the network into segments and then adding routers between the segments.
The original term for an internetwork was catenet. Internetworking started as a way to connect disparate types of networking technology, but it became widespread through the developing need to connect two or more local area networks via some sort of wide area network. The definition now includes the connection of other types of computer networks such as personal area networks.
protocol, such as The Internet Protocol is designed to provide an unreliable (i.e., not guaranteed) packet service across the network. The architecture avoids intermediate network elements maintaining any state of the network. Instead, this function is assigned to the endpoints of each communication session. To transfer data reliably, applications must utilize an appropriate Transport LayerTransmission Control Protocol (TCP), which provides a reliable stream. Some applications use a simpler, connection-less transport protocol, User Datagram Protocol (UDP), for tasks which do not require reliable delivery of data or that require real-time service, such as video streaming
Two architectural models are commonly used to describe the protocols and methods used in internetworking. The Open System Interconnection (OSI) reference model was developed under the auspices of the International Organization for Standardization (ISO) and provides a rigorous description for layering protocol functions from the underlying hardware to the software interface concepts in user applications. Internetworking is implemented in Layer 3 (Network Layer) of the model.
The Internet Protocol Suite, also called the TCP/IP model, of the Internet was not designed to conform to this model and does not refer to it in any of the normative specifications (Requests for Comment) and Internet standards. Despite similar appearance as a layered model, it uses a much less rigorous, loosely defined architecture that concerns itself only with the aspects of networking. It does not discuss hardware-specific low-level interfaces, and assumes availability of a Link Layer interface to the local network link to which the host is connected. Internetworking is facilitated by the protocols of its Internet Layer.