Do you remember when we used multi-protocol routing for IPX, AppleTalk, and TCP/IP running on the same network? In the 1980s and early 1990s many enterprises had multiple protocols running on the physical network infrastructure as "ships in the night." Cisco routers became highly adept at multi-protocol routing and the company grew in prominence as a result. Then in the early 1990s, TCP/IP won out and the internet took shape as the global network we enjoy today.
The TCP/IP protocol uses a very simple four-layer model (Application, Transport, Internet, and Link Layer). TCP/IP's layers are much simpler to remember than the seven-layer Open Systems Interconnection model (OSI model) conceived in the 1980s. To remember all those layers some use the pneumonic device (All People Seem To Need Data Processing) to remember (Application, Presentation, Session, Transport, Network, Data Link, Physical). IPv4 was the only protocol at the narrow waist of the TCP/IP hour glass, but now IPv6 has added a second protocol to the internet layer.
The internet has been under constant development since its inception in the 1970s. TCP/IP has continued to be optimized from its original design. Protocol designers have continued to create new internet transport layer protocols improve how internet applications perform. These protocols try to improve upon TCP and UDP and add congestion control and optimized throughput forwarding performance.
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