Chapter 4: Protocols Above the Data Link Layer

Chapter 4: Protocols Above the Data Link Layer

The Development of Standard Protocols

For many years, protocols above the data link layer of the OSI model were ?standard protocols? only within the product offerings of a particular vendor. Examples included IBM?s SNA (Systems Network Architecture), Xerox?s XNS (Xerox Network Services), adopted by Novell, and Digital Equipment?s DNA (Digital Network Architecture). While these protocols still enjoy wide use, other protocols are becoming dominant. One organization which has developed standards that truly transcend the boundaries between various vendor products has been the Defense Advanced Research Projects Agency (DARPA, widely referred to by its old acronym ARPA). Starting with an experimental four node network in late 1969, ARPA began interconnecting computers and computer networks at various universities and research groups to form the ARPAnet. The ARPAnet (through its successor, the Internet) has grown more than a million-fold, as has the world?s knowledge of networks, largely thanks to the research conducted on the ARPAnet. While ARPAnet covered too great a distance to be called a LAN and did not provide such LAN features as local printer sharing, it did provide file transfer, mail, and the ability to log- in to a remote computer. The protocols used to accomplish these tasks were developed at universities and research groups, were freely exchanged and improved, and have become widely used. File transfer is provided by the File Transfer Protocol (FTP), mail is provided by the Simple Message Transfer Protocol (SMTP), and remote log-in is provided by Telnet.

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Local Area Networks: An Introduction to the Technology

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Chapter 4: Protocols Above the Data Link Layer

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