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Internetworking is the practice of linking multiple computer networks together to form larger networks. Different types of networks can be connected with intermediate devices known as gateways, and once linked they act as a single large network. Internetworking was developed as a response to several issues encountered in the early days of personal computers and forms the basis of the modern Internet.
Many people use different types of networks every day without even realizing it. A businessperson who uses a smartphone to check e-mail uses a cellular network, while a home user might stream music to a laptop over a wireless network. Rural users might access their Internet Service Provider’s network over a dial-up connection, In the corporate world, large wired networks are the norm. Internetworking allows all these networks to connect to one another despite their technological differences.
The key to bridging different types of networks is the concept of packets — tiny individual units of data. Packets are the basis for modern computer networking, but aren’t confined to any one network technology. Instead, packets can be inserted into what are known as frames, which are designed for specific network technologies. This arrangement allows packets from any type of network to be used on any other type of network. Special devices that support more than one networking technology, called gateways or routers, can transfer packets between these different networks.
Internetworking evolved gradually as a response to several challenges. The earliest connections between multiple computers were “dumb” terminals with little-to-no computing power that would connect to large powerful mainframes. As personal computers (PCs) began to replace terminals, PCs were grouped into Local Area Networks (LANs). While this had many advantages, LANs were isolated and couldn’t connect to other LANs, which limited productivity. File servers, printers, and other resources couldn’t be shared between locations, and organizations with multiple locations were unable to easily exchange information.
In the early 1970s, American researchers working on a defense department funded network known as the Advanced Research Project Agency Network (ARPANET) began to investigate the possibility of linking their network to other early networks. These researches realized that early network protocols weren’t well suited to internetworking, and development of the Transmission Control Protocol and Internet Protocol (TCP/IP) began. By the end of the 1970s, ARPANET had been linked to two other networks using TCP/IP, and a crucial page in the history of the Internet had been written.
New networks continued to be connected to ARPANET in the 1980s, and an increasing number of LANs were connected to one another through ARPANET. In 1989, a network built by the National Science Foundation (NSF) replaced ARPANET. From there, regional networks were connected to the NSF’s network using TCP/IP and related protocols, and a large “network of networks” emerged — the Internet.