Review: The Design Philosophy of the DARPA Internet Protocols

The paper, The design philosophy of the DARPA internet protocols by David D. Clark [1], presents some of the early reasoning and motivations that contributed to the how the Internet was designed. The top level goal for the DARPA Internet Architecture was to develop an effective technique for multiplexed utilization of existing interconnected networks. They established a list of detailed goals ranked by their importance to DARPA project to achieve the fundamental goal.

Because this was a military project, the first goal on the list was survivability, which means the Internet should continue to supply communication service even though networks and gateways are failing. In other words, the connection should never be lost unless there is no physical path. The architecture chose the "fate sharing" approach wherein the end host is made responsible of maintaining the state information about an ongoing connection, and this lead to the use of "datagram" networks which made the internet, "connectionless". The second and third goal was to support a variety of types of services and utilize a wide variety of network technologies. Because of this, TCP and IP became two layers and the datagram became the basic building block in which multiple types of services could be constructed from. The remaining goals were: The internet architecture must permit distributed management of its resources, must be cost effective, permit host attachment with a low level of effort and the resource used in the Internet architecture must be accountable. Because these goals were lower in importance, they were less effectively met or not completely engineered but nonetheless contributed to the success of the Internet. And it was mentioned by the author that if the order of the goal list were different, a different Internet architecture would have been created. And with this, he suggests that there may be a better design of the Internet if the designer's priorities match with those of the actual users.

The author did a great job of giving the details on how and why the Internet was designed. The designers of the Internet architecture were successful in meeting their ordered list of goals which suited the need of the DARPA project. However I do agree with the author that the priorities of the list of goals have changed since the migration from military to commercial setting. Some of the goals that were lower in importance when the Internet was created that have less been effectively met might led to the Internet's deficiencies today.

It was mentioned in the paper that an alternative to interconnecting existing networks was to design a unified system which incorporated a variety of different transmission media or a multi-media network. At the time of the design of the Internet, the support for multimedia traffic was not a priority because it was not one of their needs at that time and also multimedia traffic was a minimum. However, today's Internet is heavily burdened by large amount of multimedia traffic. Is the Internet still sufficient in providing good performance? Although the Internet is flexible enough to support the various services that have been created over the years, some of these services might be wearing this flexibility.

References:

[1] D. D. Clark, "The design philosophy of the DARPA Internet protocols," ACM SIGCOMM Computer Communication Review, vol. 18, issue 4, August 1988.