Dominik Kaspar | University of Oslo (original) (raw)

Papers by Dominik Kaspar

Today, mobile devices like laptops and cell phones often come equipped with multiple network inte... more Today, mobile devices like laptops and cell phones often come equipped with multiple network interfaces, enabling clients to simultaneously connect to independent access networks. Even though applications, such as multimedia streaming and video-on-demand delivery systems, could potentially benefit greatly from the aggregated bandwidth, implementation and standardization challenges have so far hindered the deployment of multilink solutions. Previously, we have explored the benefits of collaboratively using multiple Internet connections to progressively download and play back large multimedia files. In this paper, we present an improved version of our approach that utilizes HTTP's capability of request pipelining in combination with range retrieval requests. While, in our earlier work, the optimal choice of file segmentation size presented a tradeoff between throughput and startup latency, the enhanced solution is able to overcome this tradeoff. The use of very small segments no longer impairs the efficiency of throughput aggregation, which additionally makes our solution robust against link variances and agnostic to network heterogeneity.

Multimedia streaming is increasing in popularity and has become one of the dominating services on... more Multimedia streaming is increasing in popularity and has become one of the dominating services on the Internet today. Even though user devices are often equipped with multiple network interfaces and in reach of several access networks at the same time, media streams are normally communicated over only one of the available Internet connections. In this paper, we explore the challenges and potential benefits of using multiple access networks simultaneously. Exploiting HTTP's capability of handling requests for specific byte ranges of a file, we present the implementation of a lightweight, application-layer, on-demand streaming service that requires no changes to existing servers and infrastructure. Based on real-world experiments with a multihomed host, we investigate the potential performance gains of video-on-demand playout. We achieve a bandwidth aggregation efficiency of 90% when downloading over 3 heterogeneous access networks in parallel. In addition, we analyze the effect of file segmentation on the buffer requirements and the startup latency.

With the increasing deployment of wireless technologies, such as WLAN, HSDPA, and WiMAX, it is of... more With the increasing deployment of wireless technologies, such as WLAN, HSDPA, and WiMAX, it is often the case that simultaneous coverage of several access networks is available to a single user device. In addition, devices are also often equipped with multiple network interfaces. Thus, if we can exploit all available network interfaces at the same time, we can obtain advantages like the aggregation of bandwidth and increased fault tolerance. However, the heterogeneity and dynamics of the links also introduce challenges. Due to different link delays, sending packets of the same flow over multiple heterogeneous paths causes the reordering of packets.
In this paper, we quantify the impact of network heterogeneity and the use of multiple links on IP packet reordering. We show with practical measurements, according to commonly used metrics, that packet reordering over multiple links exceeds the reordering caused by common connections in high-speed, wide-area networks. We also demonstrate that heterogeneity and reordering exceed the assumptions presented in related work. By using sufficiently large buffers, packet reordering can be avoided. However, for devices with high resource constraints, the workload of using large buffers is expensive. Sender-side solutions of dividing and scheduling a packet sequence over multiple links can reduce the buffer requirements at the receiver. Initial experiments with a static scheduler, that has knowledge of average link delay and throughput estimates, show that packet reordering can be reduced by only 38 % due to the dynamic heterogeneity of the two links.

Direction estimation inside buildings is a difficult and challenging task due to severe multipath ... more Direction estimation inside buildings is a difficult and challenging task due to severe multipath signal propagation. Numerous algorithms and techniques exist that provide high-resolution direction estimation under certain conditions and channel models; however, to our knowledge they all perform poorly at indoor environments. Here, we propose a technique that enables a receiver to achieve greater reliability in estimating source direction through some collaboration with the source. We assume that the receiver and the transmitter are synchronized and they are equipped with circular phased array antennas that have beamforming capability. If the transmitter-receiver pair always steer their main lobes into opposite directions, the spatial spectrum of the received power can be used as a mean for estimating the direction of the transmitting source. In this paper, we investigate the feasibility of this methodology, and show the achieved improvement.

Today, mobile devices like laptops and cell phones often come equipped with multiple network inte... more Today, mobile devices like laptops and cell phones often come equipped with multiple network interfaces, enabling clients to simultaneously connect to independent access networks. Even though applications, such as multimedia streaming and video-on-demand delivery systems, could potentially benefit greatly from the aggregated bandwidth, implementation and standardization challenges have so far hindered the deployment of multilink solutions. Previously, we have explored the benefits of collaboratively using multiple Internet connections to progressively download and play back large multimedia files. In this paper, we present an improved version of our approach that utilizes HTTP's capability of request pipelining in combination with range retrieval requests. While, in our earlier work, the optimal choice of file segmentation size presented a tradeoff between throughput and startup latency, the enhanced solution is able to overcome this tradeoff. The use of very small segments no longer impairs the efficiency of throughput aggregation, which additionally makes our solution robust against link variances and agnostic to network heterogeneity.

Multimedia streaming is increasing in popularity and has become one of the dominating services on... more Multimedia streaming is increasing in popularity and has become one of the dominating services on the Internet today. Even though user devices are often equipped with multiple network interfaces and in reach of several access networks at the same time, media streams are normally communicated over only one of the available Internet connections. In this paper, we explore the challenges and potential benefits of using multiple access networks simultaneously. Exploiting HTTP's capability of handling requests for specific byte ranges of a file, we present the implementation of a lightweight, application-layer, on-demand streaming service that requires no changes to existing servers and infrastructure. Based on real-world experiments with a multihomed host, we investigate the potential performance gains of video-on-demand playout. We achieve a bandwidth aggregation efficiency of 90% when downloading over 3 heterogeneous access networks in parallel. In addition, we analyze the effect of file segmentation on the buffer requirements and the startup latency.

With the increasing deployment of wireless technologies, such as WLAN, HSDPA, and WiMAX, it is of... more With the increasing deployment of wireless technologies, such as WLAN, HSDPA, and WiMAX, it is often the case that simultaneous coverage of several access networks is available to a single user device. In addition, devices are also often equipped with multiple network interfaces. Thus, if we can exploit all available network interfaces at the same time, we can obtain advantages like the aggregation of bandwidth and increased fault tolerance. However, the heterogeneity and dynamics of the links also introduce challenges. Due to different link delays, sending packets of the same flow over multiple heterogeneous paths causes the reordering of packets.
In this paper, we quantify the impact of network heterogeneity and the use of multiple links on IP packet reordering. We show with practical measurements, according to commonly used metrics, that packet reordering over multiple links exceeds the reordering caused by common connections in high-speed, wide-area networks. We also demonstrate that heterogeneity and reordering exceed the assumptions presented in related work. By using sufficiently large buffers, packet reordering can be avoided. However, for devices with high resource constraints, the workload of using large buffers is expensive. Sender-side solutions of dividing and scheduling a packet sequence over multiple links can reduce the buffer requirements at the receiver. Initial experiments with a static scheduler, that has knowledge of average link delay and throughput estimates, show that packet reordering can be reduced by only 38 % due to the dynamic heterogeneity of the two links.

Direction estimation inside buildings is a difficult and challenging task due to severe multipath ... more Direction estimation inside buildings is a difficult and challenging task due to severe multipath signal propagation. Numerous algorithms and techniques exist that provide high-resolution direction estimation under certain conditions and channel models; however, to our knowledge they all perform poorly at indoor environments. Here, we propose a technique that enables a receiver to achieve greater reliability in estimating source direction through some collaboration with the source. We assume that the receiver and the transmitter are synchronized and they are equipped with circular phased array antennas that have beamforming capability. If the transmitter-receiver pair always steer their main lobes into opposite directions, the spatial spectrum of the received power can be used as a mean for estimating the direction of the transmitting source. In this paper, we investigate the feasibility of this methodology, and show the achieved improvement.