ccr-9501-clark - The Design Philosophy of the DARPA...

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ACM SIGCOMM -1- Computer Communication Review The Design Philosophy of the DARPA Internet Protocols David D. Clark * Massachusetts Institute of Technology Laboratory for Computer Science Cambridge, MA. 02139 (Originally published in Proc. SIGCOMM ‘88, Computer Communication Review Vol. 18, No. 4, August 1988, pp. 106–114) * This work was supported in part by the Defense Advanced Research Projects Agency (DARPA) under Contract No. N00014-83-K-0125 Abstract The Internet protocol suite, TCP/IP, was first proposed fifteen years ago. It was developed by the Defense Advanced Research Projects Agency (DARPA), and has been used widely in military and commercial systems. While there have been papers and specifications that describe how the protocols work, it is sometimes difficult to deduce from these why the protocol is as it is. For example, the Internet protocol is based on a connectionless or datagram mode of service. The motivation for this has been greatly misunderstood. This paper attempts to capture some of the early reasoning which shaped the Internet protocols. 1. Introduction For the last 15 years 1 , the Advanced Research Projects Agency of the U.S. Department of Defense has been developing a suite of protocols for packet switched networking. These protocols, which include the Internet Protocol (IP), and the Transmission Control Protocol (TCP), are now U.S. Department of Defense standards for internetworking, and are in wide use in the commercial networking environment. The ideas developed in this effort have also influenced other protocol suites, most importantly the connectionless configuration of the ISO protocols 2 , 3 , 4 . While specific information on the DOD protocols is fairly generally available 5 , 6 , 7 , it is sometimes difficult to determine the motivation and reasoning which led to the design. In fact, the design philosophy has evolved considerably from the first proposal to the current standards. For example, the idea of the datagram, or connectionless service, does not receive particular emphasis in the first paper, but has come to be the defining characteristic of the protocol. Another example is the layering of the architecture into the IP and TCP layers. This seems basic to the design, but was also not a part of the original proposal. These changes in the Internet design arose through the repeated pattern of implementation and testing that occurred before the standards were set. The Internet architecture is still evolving. Sometimes a new extension challenges one of the design principles, but in any case an understanding of the history of the design provides a necessary context for current design extensions. The connectionless configuration of ISO protocols has also been colored by the history of the Internet suite, so an understanding of the Internet design philosophy may be helpful to those working with ISO. This paper catalogs one view of the original objectives
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ccr-9501-clark - The Design Philosophy of the DARPA...

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