Martin Becke

On the Use of Concurrent Multipath Transfer over Asymmetric Paths

With the deployment of more and more resilience-critical Internet applications, there is a rising demand for multi-homed network sites. This leads to the desire for simultaneously utilising all available access paths to improve application data throughput. This is commonly known as Concurrent Multipath Transfer (CMT); approaches for several Transport Layer protocols have been proposed. Combined with Resource Pooling~(RP), CMT can also fairly coexist with concurrent non-CMT flows. Current approaches focus on symmetric paths (i.e. similar bandwidth, delay and error rate). However, asymmetric paths are much more likely -- particularly for realistic Internet setups -- and efficient CMT usage on such paths is therefore crucial. In this paper, we first show the challenges of plain as well as RP-aware CMT data transport over asymmetric paths. After that, we introduce mechanisms for efficient transport over such paths. Finally, we analyse the performance of our approaches by using simulations.

Evaluation of Concurrent Multipath Transfer over Dissimilar Paths

The steadily growing deployment of resilience-critical Internet services is leading to an increasing number of Multi-Homed network sites. Asymmetric Digital Subscriber Lines (ADSL) are an inexpensive way to add a secondary Internet access connection. With the development of Multi-Path Transport Layer protocols - like Multipath TCP (MPTCP) and the Stream Control Transmission Protocol (SCTP) furnished by a Concurrent Multipath Transfer (CMT-SCTP) extension - there is also a strong interest in utilising all access connections simultaneously to improve the data throughput of the applications. However, combining network paths over ADSL with paths over other access technologies like fibre optic links implies highly dissimilar paths with significantly different bandwidths, delays and queuing behaviours. Efficient Multi-Path transport over such dissimilar paths is a challenging task for the new Transport Layer protocols under development. In this paper, we show the difficulties of Multi-Path transport in a real-world dissimilar path setup which consists of a high-speed fibre optic link and an ADSL connection. After that, we present an optimised buffer handling technique which solves the transport efficiency issues in this setup. Our optimisation is first analysed by simulations. Finally, we also show the usefulness of our approach by experimental evaluation in a real Multi-Homed Internet setup.

On the fairness of transport protocols in a multi-path environment

Today, a steadily growing number of devices contains multiple network interfaces. For example, nearly all smartphones are equipped with at least W-LAN as well as 3G/4G interfaces. In consequence, there is a rising demand for so-called multi-path transfer, which utilizes all of these interfaces simultaneously in order to maximize the payload throughput of applications. Currently, this so-called multi-path transfer is very actively discussed by the IETF, in form of the Multi-Path TCP (MPTCP) extension for TCP as well as the Concurrent Multi-path Transfer extension for SCTP (CMT-SCTP). Their larger-scale deployment in the Internet is expected for the near future. A key issue that prevents the standardization of these approaches is the fairness to concurrent TCP flows. A multi-path transfer should behave “TCP-friendly”, i.e. cause no harm to the performance of the very widely deployed TCP-based applications. In this paper, we first extend the notion of “fairness” from single-path transport to multi-path transport. Furthermore, we introduce the relevant congestion control approaches in the IETF context for single-path as well as multi-path transfer. We simulatively analyze these approaches in a couple of interesting network configuration scenarios, in order to show their behavior with special regard to the fairness definitions. Particularly, we also point out items of further discussion which are the result of the current approaches.

Applying TCP-Friendly Congestion Control to Concurrent Multipath Transfer

The steadily growing importance of Internet-based applications and their resilience requirements lead to a rising number of multi-homed sites. The idea of Concurrent Multipath Transfer (CMT) is to exploit the existence of multiple paths among endpoints to increase application data throughput. However, handling the congestion control of each path independently lacks of fairness against non-CMT flows. In this paper, we describe our approach of combining CMT with the idea of Resource Pooling (RP) in order to achieve a performance improvement over non-CMT transfer while still remaining fair to concurrent flows on congested links. Unlike existing approaches which adapt classic TCP to a multi-homed CMT protocol, our approach does not depend on specific characteristics of TCP. Instead, we base on already entrenched functional blocks of CMT transfer, on the example of the CMT-enabled SCTP (Stream Control Transmission Protocol). In a simulative proof-of-concept analysis, we show that our approach -- while relatively simple -- is already quite effective.

Simulation and Experimental Evaluation of Multipath Congestion Control Strategies

The need for service resilience is leading to a steadily growing number of multi-homed Internet sites. In consequence, this results in a growing demand for utilising multiple Internet accesses simultaneously, in order to improve application payload throughput during normal operation. Multi-path Transport Layer protocol extensions - like Multi-Path TCP (MPTCP) for TCP and Concurrent Multipath Transfer for SCTP (CMT-SCTP) - allow applications to make use of such network topologies. However, since TCP - which constitutes the basis of most Internet applications - and its congestion control procedures have been designed under the assumption of single-homed sites, fairness issues may arise by the usage of multipath transport. These issues are addressed by advanced congestion control approaches, which have already been examined by simulations. However, real-life network measurements are missing. In this paper, we perform an experimental proof-of-concept evaluation of several multipath congestion control strategies, which are currently under discussion within the IETF in the context of MPTCP as well as CMT-SCTP. Particularly, we validate effects that have been observed in simulations, in order to trigger further discussions on multipath congestion control. Also, our goal is to provide insight into the different approaches to support the ongoing IETF standardisation activities on multipath transport protocols.

Implementation and evaluation of concurrent multipath transfer for SCTP in the INET framework

The steadily growing importance of resilience-critical Internet applications leads to a rising number of multi-homed sites and systems. But since the protocols of the classical Internet - particularly TCP - assume a single access path only, the number of programs supporting multiple network paths is still small. The Stream Control Transport Protocol (SCTP), which is an advanced general-purpose transport protocol and the possible successor of TCP, brings the support of multi-homing into the applications. For technical reasons, SCTP uses one network path for data transmission and utilizes the other paths for backup only. An extension to support the load balancing of user data onto multiple paths in order to increase the payload throughput is Concurrent Multipath Transfer for SCTP, denoted as CMT-SCTP. In this paper, we describe our CMT-SCTP extension for the SCTP model provided by the INET framework. By using proof-of-concept simulations, we furthermore demonstrate its usability and configuration parameters.

Comparison of Multipath TCP and CMT-SCTP based on intercontinental measurements

The market penetration of access devices with multiple network interfaces has increased dramatically over the last few years. As a consequence, there is a strong interest to use all of the available interfaces concurrently to improve data throughput. Corresponding extensions of established Transport protocols are receiving considerable attention within research and standardization. Currently two approaches are in the focus of the IETF: The Multipath TCP (MPTCP) extension for TCP and the Concurrent Multipath Transfer extension for SCTP (CMT-SCTP). This paper evaluates and compares implementations of these two loadsharing protocols by using both lab measurements and intercontinental testbed realized via the Internet between Europe and China. The experiments show that some performance critical aspects have not been taken into account in previous studies. Furthermore, they show that the simple scenario with two disjoint paths, which is typically used for evaluation, does not sufficiently cover the real Internet environment. Based on these insights, we highlight that the different path management strategies of the two protocols have a significant impact on their performance in real Internet scenarios.

WebRTC Data Channels

Browser-to-browser real-time communication is making rapid progress in the standardization process, both in the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C). These advancements cover many aspects, such as interface definitions, protocol mechanisms and security. Many scenarios discussed show that interfaces and standards can serve as a foundation for interoperable real-time multimedia applications that are easy to implement. In addition to the transfer of real-time-media data, the currently discussed protocol stacks also support transfer of non-media data. This article gives a brief top-down discussion of how the standardization efforts reflect the use cases of non-media data transfer, which use cases could be addressed, and how technologies are applied to achieve the goals. Furthermore, it provides an insight into specific protocol mechanisms as well as unresolved issues for future work.

Data channel considerations for RTCWeb

Browser-to-browser communication is a hot topic in the network research community. The goal of developing and standardizing RTCWeb for real-time communication is to enhance the communication experience over the Internet. The RTCWeb protocol stack provides a service for several use cases, which includes media as well as non-media data transfer. Therefore, it adapts some established protocols like SCTP for a new common goal. Since real-time communication comes with the inherent need for low end-to-end delay, this article will discuss possible enhancements to SCTP that will improve the RTCWeb service in that regard.

A Future Internet architecture supporting multipath communication networks

The classic layered OSI reference model has reached its limits for the Internet of today. In this paper, we propose a clean-slate conceptual design of a new architecture as a contribution to the ongoing discussion on the Future Internet. We address the shortcomings of the layered model by redesigning the classical model. Our approach differs from the concepts found in prior work, which focus on special parts of the problems (such as the application, the service or the event) by staggering back a couple of steps and trying to see the requirements from a different perspective. Our concept - which is denoted as Encapsulated Responsibility-Centric Architecture Model (ERiCA) - focuses on determining the responsibilities by using different planes in addition to a partitioning of the network into different decision domains. With this partitioning, we can reduce the complexity of providing a certain service.