A Flexible End-to-End Protocol Framework

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Support for emerging network applications requires that the basic delivery service provided by the network infrastructure be augmented with services that are implemented in the end systems connected to the network. Examples of such services include: recovery from messages lost in the network; encrypting transmitted information; verifying that received information was not forged or modified in transit; adjusting the rate of transmission to available bandwidth; and attaching identifying information to the transmitted data so that the receiver can process it even if it arrives out of order. Some of these services are provided today by protocols that are organized in layers. Although it is a very useful paradigm for organizing network functionality, research and experience have identified several problems with layering as it is applied to end-to-end functions (i.e. those that are implemented in the end systems rather than the network). In particular, layering causes services to be too coarsely grouped together, so that applications may have to make use of some services they don't need in order to get others. (For example, TCP forces an application that needs congestion control to also accept reliability -- which, if not needed, just adds unnecessary overhead.) Layering also causes functions to be implemented in more than one place in the stack, and hides information that might be useful for improving efficiency. This project aims to develop and deploy a platform for end-to-end functions that incorporates the lessons learned about protocol design and implementation over the last several years. The platform, which is called Tau, is not intended to identify all the functions that applications may ever require, but rather to streamline the process of incorporating those functions into systems and applications as they are identified and developed. The approach involves developing a simple conceptual framework and a common message format that supports optimization of common processing paths, while also allowing for extension at a (modest) cost in efficiency. Tau has three main features. The first is an explicit composition mechanism (a metaheader) that promotes modularity of function and implementation but avoids the problems associated with layering. The second is a generic protocol interface, which allows individual protocol functions to be implemented separately, then composed efficiently, to provide just the services required by the application. In developing this feature, the project will contribute new methods of integrating code for fast execution while preserving modularity at the source code level. The third feature is a set of protocol functions that can be extended to include new services in addition to the traditional ones mentioned above. Information on the Tau Project is available via the World-Wide Web at http://www.cc.gatech.edu/fac/Ken.Calvert/Tau.html