Andreas Könsgen

Enhancing fairness and congestion control in multipath TCP

With the advancement in technology, today most of the end-host devices are equipped with multiple wired/wireless interfaces and capable of using them in parallel. This has led to research in taking advantage of utilizing additional available network resources simultaneously such as multiple paths between the multi-homed end devices to achieve better performance. In this regard, new multipath transport protocols such as Multipath TCP and Concurrent Multipath Transfer SCTP are being designed and developed. On one hand these new protocols need to optimize the usage of the available multiple paths efficiently with a suitable scheduler while on the other hand they should be also fair to the existing transport protocols like TCP and SCTP, especially in a congested environment. This paper illustrates and compares the solutions that have been proposed to ascertain that Multipath TCP can yield an improved performance while being fair to standard TCP. In addition, this paper highlights improvements to two of the proposed congestion control solutions-Dynamic Window Coupling and Opportunistic Linked Increases Algorithm. A brief look into hybrid scheduling mechanisms is also provided with a special interest in minimizing the overall reordering delay and to capture the dependency on the receiver buffer size. It is shown that the proposed solutions give good performance in most of the different bottleneck scenarios while staying friendly to legacy transport protocols.

Mobility management for an integrated network platform

This paper initially, describes the NOMAD test-bed being set up at ComNets for network integration to integrate various bearer technologies (GSM, GPRS, WLAN, Ethernet). It is based on different Mobile IP versions (IPv4 and IPv6) and software for ad-hoc networking using the AODV (Ad-hoc On Demand Vector routing) protocol. The second section describes the Mobile IP implementations and the improvements achieved in the area of handoff delays. The paper also details the results obtained from the ad-hoc network, to determine the performance of AODV when new nodes are added, and explains future research.

Design issues of Mobile IP handoffs between General Packet Radio Service (GPRS) networks and wireless LAN (WLAN) systems

This paper describes the system design and implementation of a demonstrator prototype, running at University of Bremen, which implements Mobile IP handoffs between GPRS and WLAN systems. Mobile IP requires public IP addresses but there is no support of such IP addresses by most mobile operators. To solve the problem of NAT (network address translation) and firewalls resulting from this, several concepts are available. This paper presents a practical implementation of one such concept where Mobile IP handoffs are realised using tunneling functions and an additional Mobile IP foreign agent to provide GPRS network access. Furthermore, this paper presents measurement results of the test bed and shows the quality of the Mobile IP handoffs.

Performance and fairness comparison of extensions to dynamic window coupling for Multipath TCP

With the onset of multiple wireless technologies, the end-host devices of today are multi-homed. This has led to research in the simultaneous use of multiple paths between the multi-homed end devices. New multipath transport protocols such as Multipath TCP and Concurrent Multipath Transfer SCTP need to be fair to the existing transport protocols like TCP and SCTP in a congested network. One way of being fair is to couple the congestion control mechanisms of the protocol over its multiple utilized paths. This paper illustrates and compares the solutions that have been proposed to ascertain that Multipath TCP can yield an improved performance while being fair to standard TCP. In addition, this paper highlights improvements to one of the proposed solution - Dynamic Window Coupling. It is shown that the new solution performs best in most of the different scenarios of bottlenecks in a network with a higher preference given to being friendlier to TCP.

Transmit Power Control Algorithms in IEEE 802.11h Based Networks

In this paper, transmit power control algorithms are discussed to support the spectrum management required by the wireless LAN standard IEEE 802.11h. A centralised algorithm for the infrastructure mode and an algorithm working on a link-by-link basis for ad-hoc networks are discussed. The performance of the algorithms, in particular the reduction of the transmit power and the enhancements of the QoS parameters delay and throughput are considered. It is shown that both algorithms significantly reduce the transmit power and improve the quality-of-service characteristics of wireless networks

Responsiveness of future telecommunication networks under disaster situations

Disaster situations are a challenge for network operators because they result in an extraordinary large number of calls being opened simultaneously compared to normal operating conditions. The Quality of Service (QoS) and Quality of Experience (QoE) for the end user can be widely affected by peak loads and result in severe degradation, basically due to congestion on bottlenecks inside the network. In disaster situations, however, a high reliability of the connections is in particular required. In order to overcome the beforementioned issue, an extension for the well-known TCP named Multipath TCP (MPTCP) is investigated which delivers a TCP stream to different subflows sent over multiple interfaces and paths. Since MPTCP is an end-to-end transport-layer solution, it is independent of support by the network providers infrastructure and also works across multiple providers by delivering individual subflows over different networks. Simulation results show that MPTCP is suitable to reduce the load on individual access interfaces and helps to avoid congestion inside the network by shifting traffic to less loaded links so that a better QoS can be maintained. The performance of the network is enhanced by better utilization of the network capacity without increasing the link capacities.

A Two-Stage QoS Aware Scheduler for Wireless LANs Based on MIMO-OFDMA-SDMA Transmission

In this paper, a QoS-aware cross-layer scheduler for wireless LANs is introduced which can handle parallelised transmissions which are provided by OFDMA or SDMA. The scheduler includes two stages: in the hardware-independent stage, data flows are selected according to their QoS requirements such as throughput and delay. In the hardware-dependent stage, the channel resources are adaptively allocated to the flows according to the user priorities. All flows with a sufficiently high channel capacity are transmitted in parallel by assigning different OFDMA subcarriers or different spatial subchannels to the users. It is shown that the proposed QoS aware scheduler efficiently uses the channel resources in case of TDMA, OFDMA or SDMA and meets the quality-of-service requirements of time-critical flows under varying load and channel conditions.

TEACHING THE INTERNET OF THINGS

Teaching the Internet of Things has become vital in engineering, but also very challenging. This is mainly due to the almost unbelievable variety of available systems, hardware and software components, and online resources. This column discusses how we, at the University of Bremen, approached this problem: with hands-on experience and concept abstraction.

An Enhanced Cross-Layer Two-Stage Scheduler for Wireless LANs

In this paper, a QoS-aware cross-layer scheduler for wireless LANs is introduced which allows the control of a number of data flows according to QoS requirements of the respective applications. It is based on a two-stage concept: The MAC layer scheduler uses an importance function to calculate the priority of a particular flow, whereas the PHY layer scheduler considers the channel conditions of a MIMO-TDMA transmission. It is shown that with the concept presented here, throughput and delay requirements of time-critical applications can be met.

Enhancing Quality of Experience (QoE) assessment models for video applications

Video applications are becoming the key services in todays networks (both fixed networks and mobile networks). Consideration of video service quality has become essential to provide the end users with satisfying Quality of Experience (QoE). In order to evaluate and manage the video quality, methods for QoE assessment are desired to estimate the service quality perceived by the end users. In this paper, we study a number of existing objective quality assessment models for assessing the QoE of video applications, and compare their performance with simulations to find out their individual advantages and limitations to use in practice. To overcome the shortcomings of the existing models, this paper proposes an enhanced QoE model which considers a wide range of codec rates and video formats, and moreover considers the packet losses and video content dependence in quality assessment. Simulation results show that the proposed QoE model can be applied for evaluating the quality of different video sources in the Long Term Evolution (LTE) networks, considering the lossy property of mobile networks. In addition to the objective QoE methods, we also plan to carry out subjective tests in the lab as well as in the real system for the subjective evoluation of QoE.