A Flexible End-to-End Protocol Framework

对新兴网络应用的支持要求通过在连接到网络的终端系统中实现的服务来增强由网络基础设施提供的基本递送服务。 这类服务的例子包括：从网络中丢失的信息中恢复信息;对传输的信息进行加密;核实收到的信息在传输过程中没有被伪造或修改;根据可用带宽调整传输速率;以及在传输的数据中附上识别信息，以便接收方即使在数据到达时顺序不对也能进行处理。 这些服务中的一些现在是由分层组织的协议提供的。 虽然它是组织网络功能的一个非常有用的范例，但研究和经验已经确定了分层应用于端到端功能（即在终端系统而不是网络中实现的功能）时的几个问题。特别是，分层会导致服务过于粗糙地组合在一起，因此应用程序可能不得不使用一些它们不需要的服务来获取其他服务。 (For例如，TCP强制需要拥塞控制的应用程序也接受可靠性--如果不需要，只会增加不必要的开销。 分层还导致函数在堆栈中的多个位置实现，并隐藏可能对提高效率有用的信息。 该项目旨在开发和部署一个端到端功能平台，其中纳入过去几年在协议设计和执行方面吸取的经验教训。 该平台被称为Tau，其目的不是确定应用程序可能需要的所有功能，而是简化将这些功能纳入系统和应用程序的过程。 该方法涉及开发一个简单的概念框架和一个通用的消息格式，支持优化通用处理路径，同时还允许以（适度）的效率成本进行扩展。 Tau有三个主要特点。 第一种是显式组合机制（元头），它促进了功能和实现的模块化，但避免了与分层相关的问题。 第二个是通用协议接口，它允许单独实现各个协议功能，然后有效地组合，以提供应用程序所需的服务。 在开发此功能时，该项目将贡献新的方法来集成代码以实现快速执行，同时在源代码级别保持模块化。 第三个特征是一组协议功能，除了上述传统的服务之外，还可以扩展这些功能以包括新的服务。 有关Tau项目的信息可通过万维网http://www.cc.gatech.edu/fac/Ken.Calvert/Tau.html获得

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