Analysis and Enhancement of Multipath Mechanisms Focusing on the OSI Transport Layer

终端系统和网络组件通过多条网络路径互连(多宿主)是提高连接可用性的经典方法。由于现代终端设备中具有多个网络接口的可用性，以及支持多宿主的传输协议的标准化，如多路径-TCP和SCTP，该方案也变得对终端用户具有吸引力。除了错误情况下的纯冗余之外，另一个问题是是否可以同时使用多条路径以增加数据吞吐量。这种被称为并发多路径传输(CMT)的方法一方面需要调整重要的协议功能，另一方面以在单路径传输中不出现的方式影响网络中资源的利用。多条路径的同时使用带来了新的自由度，但也增加了复杂性。这一事实以及所涉及的各种机制之间的相互关系还没有得到充分的了解，这就产生了研究的根本需要。遗留方法的重点是基本功能，而不是最佳使用。然而，使用了公知的机制，这些机制被设计用于通过单一路径的最佳传输。到目前为止，对于通过多条路径的最佳传输的适当机制的选择以及适当的扩展或此类机制的新定义(如果适用)都没有进行充分的研究。在其他问题中，用于路径选择和将数据流分配到路径的算法对于满足应用要求的可用资源的最佳使用是必需的。此外，必须调整或重新定义例如与传输资源的公平共享有关的基本定义，并且必须重新评估对于当前协议而言典型的不同功能的耦合，例如拥塞控制和公平性。这些通用的、与协议无关的结果显著影响了支持CMT的传输协议的设计。该项目的一个主要目标是系统地研究CMT的新自由度和相关的基本挑战。这方面的起点是目前讨论的提案和申请者在这方面已经取得的见解。对资源利用的最优化问题进行数学建模可望产生重要的结果。该项目的结果应该是针对支持CMT的协议的主要通用设计方法，该方法结合了新的要求和可能性。在现行议定书提案的现行定义中采用这一办法，将显示出实际的好处。

The interconnection of end systems and network components by multiple network paths (multihoming) is a classical approach to increase the availability of the connectivity. Due to the availability of multiple network interfaces in modern terminal devices and the standardization of transport protocols with multihoming support such as Multipath-TCP and SCTP, this scheme also becomes attractive for the end user. Beyond the pure redundancy in case of errors, another question is whether a simultaneous usage of multiple paths is possible in order to increase the data throughput. This approach termed Concurrent Multipath Transfer (CMT) on the one hand requires adaptations of important protocol functions, and on the other hand affects the utilization of the resources in the network in a manner which does not appear in a single-path transmission. The simultaneous use of multiple paths opens up new degrees of freedom but also increases complexity. This facts as well as the correlations among various mechanisms involved, which are not sufficiently understood yet, create a fundamental need for research.The focus of legacy approaches aims at the basic functionality and not on the optimum usage. Well-known mechanisms are used which were, however, designed for an optimum transport via a single path. Both the selection of suitable mechanisms for the optimum transport via multiple paths as well as suitable extensions or, if applicable, new definitions of such mechanisms are not sufficiently investigated up to now. Among other issues, algorithms for the path selection and the allocation of the data streams to the paths are necessary for an optimum usage of the available resources fulfilling the requirements of the application. Furthermore, basic definitions, e.g., related to the fair share of transmission resources have to be adapted or newly defined and the, often implicit, coupling of different functions, e.g., congestion control and fairness, which is typical for current protocols have to be reevaluated. These generic, protocol-independent results significantly affect the design of the CMT-enabled transport protocols.A major goal of the project is the systematic investigation of the new degrees of freedom and the related fundamental challenges of a general application of CMT. The starting point for this are the currently discussed proposals and the insights which have already been achieved by the applicants in this context. A mathematical modelling of the optimization problem for the resource utilization is expected to yield important findings. The outcome of the project should be a largely generic design approach for CMT-enabled protocols which incorporates the new requirements and possibilities. The practical benefit will be demonstrated by a applying this approach in the on-going definition of the current protocol proposals.