WebTP: A User-Centered Web Transfer Protocol

万维网现在是一个重要的通信基础设施forsociety。然而，Web建立的基础在很大程度上是临时的和随意的，协议框架由超文本传输协议（HTTP）组成，位于Internet的通用可靠传输协议（TCP）之上。HTTP over TCP的性能存在许多缺陷，这些缺陷都源于TCP的字节-流语义通常与用户目标以及终端客户机和服务器的性能能力不一致。早期已经提出了几种临时补救措施来弥补这些缺陷，例如并行连接、持久连接和ACK调步。然而，所有这些解决方案都受到向后兼容性假设的过度限制。我们相信，现在是时候采用一种整体和综合的方法，体现在一种专门为Web定制的新传输协议中。在此，我们提出了一组研究任务，研究，设计，实现，测试和评估我们的新的“WebTransport Protocol”或WebTP。我们的方法是基于一个概念模型的用户验证，应用程序语义，网络和客户端状态，和一个灵活的协议，反映了这种语法和语义。概念模型强调文档结构、网络状态和用户偏好之间的相互作用。我们的研究原型将利用TCP的成熟和高度成功的拥塞控制框架，并通过将用户需求纳入设计循环来大大改进现有的Web协议。为此，我们将应用应用层框架（ALF）的原则来设计WebTP。ALF说，为了优化应用程序内部和网络上的通信路径，应用程序的语义（即其用户需求）应该明确地反映在其网络协议的设计中。虽然ALF已被采用在现代的协议，如实时传输协议（RTP），矛盾的是，它还没有被系统地应用到以前存在的应用程序，如Web.We将研究以下问题：* 我们如何最好地结构ALF为基础的Web协议方面ofcongestion控制算法，丢失恢复计划，packet framingmethodology，报头格式，工具包API，等等？这些设计决策如何影响网络性能、用户满意度、协议复杂性和服务器负载？*那么，客户端如何以最不显眼的方式引出用户的偏好呢？接收方（客户端）如何了解服务器Web数据的内容结构，并将该结构与其对网络状态和用户偏好的估计结合联合收割机，以控制通过WebTP的选择性传输？功能和状态信息应该如何在服务器（服务器或代理）、客户机和用户之间分布，设计和性能的权衡是什么？WebTP如何随着速度的提高和更快的客户端而扩展？我们对这些问题的解决方法借鉴了网络工程和通信理论、信号处理和随机控制。 我们将使用来自INDEX项目的现有网络仿真基础设施来全面测试和评估WebTP。这个项目有可能极大地影响我们对Web传输的思考方式，并将进一步贡献一种设计方法，一个实际的协议体系结构，以及性能分析和结果。我们相信，我们的WebTP版本将展示出巨大的改进，并为进一步的发展铺平道路。

The World Wide Web is now a critical communication infrastructure forsociety. However, the foundations on which the Web is built are largely adhoc and haphazard, with a protocol framework consisting of the hypertexttransport protocol (HTTP) layered on top of the Internet's universalreliable delivery protocol-the transmission control protocol (TCP).Consequently, the performance of HTTP over TCP suffers from a number ofdeficiencies that are all rooted in the fact that TCP's byte-streamsemantics are often at odds with user goals and the performancecapabilities of end clients and servers.Several ad hoc remedies have been proposed earlier to compensate for thesedeficiencies, e.g. parallel connections, persistent connections, and ACKpacing. However, all these solutions are overly constrained by thepresumption of backward compatibility. We believe that the time has come toadopt a holistic and integrated approach embodied in a new transportprotocol tailored specifically for the Web. Herein, we propose a set ofresearch tasks to study, design, implement, test and evaluate our new ``WebTransport Protocol" or WebTP.Our approach is based on a conceptual model of user validation, applicationsemantics, network and client states, and a flexible protocol that reflectsthis syntax and semantics. The conceptual model emphasizes the interactionbetween document structure, network state, and user preferences. Ourresearch prototype will leverage the well-established and highly successfulcongestion control framework of TCP and vastly improve upon the existingWebprotocols by bringing user requirements into the design loop. To do so, wewill apply the principles of Application Level Framing (ALF) to the designof WebTP. ALF says that to optimize communication paths within theapplication and across the network, an application's semantics (i.e. itsuser requirements) should be explicitly reflected in the design of itsnetwork protocol. Although ALF has been adopted in modern protocols likethe Real-time transport protocol (RTP), paradoxically it has not beensystematically applied to previously existing applications like the Web.We will study the following questions:* How do we best structure the ALF-based Web protocol in terms ofcongestion control algorithms, loss recovery schemes, packet framingmethodology, header formats, toolkit APIs, and so forth? How do thesedesign decisions impact network performance, user satisfaction, protocolcomplexity, and server load?* How then does the client elicit user preferences in the least obtrusivefashion?* How does the receiver (client) learn of the content structure of aserver's Web data and combine that structure with its estimate of networkstate and user preferences to control selective transmission via WebTP?* How should functionality and state information be distributed among thesource (server or proxy), client, and user and what are the design andperformance tradeoffs? How does WebTP scale with increased speed and fasterclients?Our approach to these questions draws upon network engineering andcommunication theory, signal processing and stochastic control. We willuse existing network emulation infrastructure from the the INDEX Project tocomprehensively test and evaluate WebTP. This project holds the potentialto dramatically impact the way we think about Web transport and willfurther contribute a design methodology, an actual protocol architecture,and performance analysis and results. We believe that our versions of WebTPwill demonstrate dramatic improvements and pave the way for furtherdevelopments.