on the 'The Design Philosophy of the DARPA Internet Protocols'

The paper enumerated and described the various goals behind the DARPA Internet Project which gave birth to what we know now as the Internet; at the same time discussed their relations to the mechanisms which were chose to achieve those goals. The Internet started out as a military funded research project under the Defence Advanced Research Projects (DARPA) of the DoD of the USA.

The main goal of its inception was to provide a way for multiplexed internetwork communications among existing heterogeneous and disparate network infrastructures. Packet switching was chose as the technique for multiplexing since most of the existing networks employ packet switches.

Several second level goals were considered in its design, which proved to have great effects to what have become of it now. Survivability which relates to service availability and continuity tops among the second level goals of the design of the Internet. For example, any interruptions in some part of the network should not disrupt the usability of the whole infrastructure. Also interruptions at the lower layers of the infrastructure should be hidden or abstracted from the application level. Support for multiple services came second. So the designers of the Internet wanted to bring as many services to the Internet as possible. If we remember, reliability was the critical design requirement of the TCP. For some services i.e. real-time applications, the reliability of the TCP comes with a cost, performance degradation. The decision to formally define the boundary (layering) between TCP and IP was made, and another transport layer protocol was created, which is the User Datagram Protocol. UDP provides application a low level interface in performing their needs of internetwork communications, resulting to better control, flexibility and performance. Also, they wanted that the Internet will be able to accommodate various types of networks. Other goals which set at the bottom of the Internet priority list where (4) a mechanism for distributed management of its resources should be provided, (5) it must be cost effective, (6) host attachment must be easy, (7) resources in the Internet must be accountable. Interestingly, (7) has not been fully realized until now.

Surprisingly, there was no explicit mention of security in the original design of the Internet. Survivability was there, but I believe its notion relates more on the physical aspect of the infrastructure. The inclusion of the idea of a datagram as a building block element I think is one of the great realizations of the designers of the Internet. It gives developers better control and flexibility in meeting the networking aspects of the applications that they develop. Fate-sharing is another design decision that has proved to be critical in the development of the Internet. The notion of maintaining state information of communications at the end points only, enabled hosts to be less dependent on the performance of intermediary points in the networks. This provides service continuity on cases when some disruption happens at subset of the network.