Review: The Design Philosophy of the DARPA Internet Protocols

The design philosophy of the DARPA internet protocols by David D. Clark [1], presents that the current design of the protocols is the result evolution, and the features of TCP/IP are decided by early goals of Internet architecture. DAPRA Internet Architecture fundamental goal was to develop an effective technique for multiplexed utilization of existing interconnected network. In order to achieve this goal, they established detailed set of goals for the development of the Internet architecture. These goals have a set of priorities, which highlighted the design decisions within the architecture. The most important goal was continuity of communication despite loss of networks, which decided that the Internet should use datagram network design. In order to support multiple types of communication services, Transmission Control Protocol (TCP) and Internet Protocol (IP) are separated into two layers and IP becomes the based protocol of protocol stack. Interconnectivity among variety of network technologies also leads the Internet architecture becomes to be TCP and IP layers. Flexibility between a number of services is achieved by making a basic assumption, that network can transport a packet or datagram and should be delivered with reasonable reliability. All features of TCP/IP protocol stack are tailored to the goals of early Internet.

I also understand that Internet architecture is triumphant to meet the most important goals of early demand, but was not designed to meet future priorities. It doesn’t thoroughly satisfy the other goals in the architecture like accountability and distributed management. There should be an improvement to be done in order to design the protocols within the said set of goals effectively. Detailed understanding on the layers of Internet could be used in achieving these so called limitations. But I don’t mean that they should immediately satisfy all priorities, but rather the ability to adapt to meet the priorities of future. Aside from these priorities, performance should be put into consideration in the designing phase. Because of today’s enormous network systems, performance in terms of speed and reliability could be a factor that could determine the success or failure of this redesigning.

We still rely on a version of TCP/IP today. It has proven to be very challenging to improve the present protocols, if not entirely infeasible, to change the underlying architecture of the Internet at this point. The push to switch to IPV6 is one example of the difficulties involved. By implementing this, we can achieve more IP addresses than the current IPV4.

Scientists should recognize that in ever changing environment of the Internet priorities often change. It is not the ability to immediately satisfy all priorities, but rather the ability to adapt to meet the priorities of the future. It was a large step to move from networks which had been traditionally circuit switched to the packet switched Internet. The use of datagrams gives us more flexibility in dealing with unlike systems then continuous streams would allow. It is also important to realize that sessions can still be used in the datagram model by creating a virtual circuit. The issue of survivability which was once so important to the military is pretty much non-existent due to the extreme redundancy built into the topology of the Internet today. Much more important today is the issue of performance. Performance was not a large issue when the Internet was created, but could now be considered the most important issue. TCP/IP has adapted to fit the current day needs, but it is evident by the ordering of priorities when created that the protocol was not designed for the present day Internet.

Generally, the paper [1] is a good material for me to understand the Internet design philosophies.

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

Review: End-to-End Arguments in System Design

End-to-end arguments in system design by J.H. Saltzer, D.P. Reed and D.D. Clark [1] presents a design principle called end-to-end argument, which proposes that functions that were usually developed at low levels modules in a distributed system should be excluded from those modules. Instead, it recommends that these functions should be placed on the higher level modules, closer to the application that uses the function, in order to provide the essential functionality. It also states that when a module consists of low level functions, there are instances that it may not be able to execute the functionality as what the higher level application requires to do. But on the other hand, there are cases that low level functions provide better efficiency and performance. Thus, this principle should not be treated as an absolute but as a valuable guide for placing functionality in a communication system.

The end to end arguments are a set of design principles on how the Internet has been designed [2]. But due to the expansion of Internet, from individual to commercialization purpose, there is a rising threat of rethinking the Internet's original design principles. Few numbers of new requirements have emerged for the Internet and its applications and these will be fulfilled through the addition of new mechanism in the core of the network.

While multiple forces seem to support the alteration within the Internet mechanism that may be inconsistent with the end to end arguments, we can’t refute the contribution of end to end arguments in the preservation of flexibility and openness of the Internet. They also allow new applications to be developed. End to end implementations are supported by the need to ensure appropriate service, and to facilitate network transparency, and decentralism. Consequently, the simplicity of placing certain functionality to lower-level modules is applicable to certain service and can have an impact in terms of its performance.

References:
[1] J. H. Saltzer, D.P. Reed and D. D. Clark, "End-to-end arguments in system design," ACM Transactions in Computer Systems, vol. 2, no. 4, pp. 277-288, November 1984.
[2] M. S. Blumenthal and D. D. Clark, "Rethinking the design of the Internet: The end to end arguments vs. the brave new world," ACM Transactions on Internet Technology, vol. 1, no. 1, pp. 70-109, August 2001.