Review: The Design Philosophy of the DARPA Internet Protocols

David D. Clark's paper entitled "The Design Philosophy of the DARPA Internet protocols" describe the goals and considerations that drove the design of the Internet protocols, in particular that of TCP/IP. The fundamental goal was to develop a technique to interconnect the different existing networks, ARPANET and the ARPA packet radio network. The primary goal was for the connection to survive in the face of failure. Other goals that were prioritised included flexibility of network services and interoperability between different varieties of networks. Also included as goals are the distributed management of resources and cost effectivity, although they were not as effectively met.

The paper then describes datagrams and TCP/IP with respect to the motivations that were previously mentioned. Datagrams are the "basic building blocks" upon which a variety of different service types can be built and assume a "minimum network service". However, datagrams do not implement more complex features like reliability and buffering. TCP/IP is a simplified version of the ARPANET protocol that implements some reliability features such as flow control, acknowledgement and retransmission, as well as packet fragmentation to support different data sizes.

Clark identifies a weaknesses in the Internet architecture where certain needs, such as accounting, resource management and separate network administration are not met. In particular, the datagram model means that each host must treat packets separately instead of being part of a defined sequence. A new building block called "flow" is proposed where a sequence of packets will be identified without assuming any particular type of service. Gateways will maintain the state of the flows that are passing through them although the type of service will still be enforced by the end points. At present we can see how this idea has been implemented in schemes such as firewalls and quality-of-service (QoS) applications installed in gateway machines.

This paper addresses some shortcomings of the Internet architecture by by slightly changing the original assumption of TCP that only end-points should care about the packets being transmitted through the network. Later papers will build upon the idea of involving gateways and other machines aside from the end-point in implementing communications protocols.

This paper shows how the original design of the Internet conceived and the shortcomings that arise as the purpose of the Internet changed over time. Because of this I would recommend that this paper be included as part of the CS 255 reading list.

References

David D. Clark, "The Design Philosophy of the DARPA Internet Protocols", 1988