Improving SCTP retransmission delays for time-dependent thin streams

A large number of network services rely on IP and reliable transport protocols. For applications that provide abundant data for transmission, loss is usually handled satisfactorily, even if the application is latency-sensitive (Wang et al. 2004). For data streams where small packets are sent intermittently, however, applications can occasionally experience extreme latencies (Griwodz and Halvorsen 2006). As it is not uncommon that such thin-stream applications are time-dependent, any unnecessarily induced delay can have severe consequences for the service provided. Massively Multiplayer Online Games (MMOGs) are a defining example of thin streams. Many MMOGs (like World of Warcraft and Age of Conan) use TCP for the benefits of reliability, in-order delivery and NAT/firewall traversal. It has been shown that TCP has several shortcomings with respect to the latency requirements of thin streams because of the way it handles retransmissions (Griwodz and Halvorsen 2006). As such, an alternative to TCP may be SCTP (Stewart et al. 2000), which was originally developed to meet the requirements of signaling transport. In this paper, we evaluate the Linux-kernel SCTP implementation in the context of thin streams. To address the identified latency challenges, we propose sender-side only enhancements that reduce the application-layer latency in a manner that is compatible with unmodified receivers. These enhancements can be switched on by applications and are used only when the system identifies the stream as thin. To evaluate the latency performance, we have performed several tests over various real networks and over an emulated network, varying parameters like RTT, packet loss and amount of competing cross traffic. When comparing our modifications with SCTP on Linux and FreeBSD and TCP New Reno, our results show great latency improvements and indicate the need for a separate handling of thin and thick streams.     

Storage system support for continuous-media applications. Part 1. Requirements and single-disk issues

A multimedia storage system plays a vital role for the performance and scalability of multimedia servers. To handle the server load imposed by increased user access to on-demand multimedia streaming applications, new storage system solutions are needed. Multimedia storage systems store and retrieve data from storage devices and manage related issues including data placement, scheduling, file management, continuous data delivery, memory buffering, and prefetching. For high-data-rate multimedia systems, storage systems have long been viewed as a primary bottleneck for two reasons. First, multimedia applications have a much higher storage system load than previous applications. Second, storage devices have become only marginally faster compared to increased processor and network performance. This increasing speed mismatch has fueled a search for new storage structures and file system storage and retrieval mechanisms     

The partial migration of game state and dynamic server selection to reduce latency

Massively multi-player online games (MMOGs) have stringent latency requirements and must support large numbers of concurrent players. To handle these conflicting requirements, it is common to divide the virtual environment into virtual regions. As MMOGs are world-spanning games, it is plausible to disperse these regions on geographically distributed servers. Core selection can then be applied to locate an optimal server for placing a region, based on player latencies. Functionality for migrating objects supports this objective, with a distributed name server ensuring that references to the moved objects are maintained. As a result we anticipate a decrease in the aggregate latency for the affected players. The core selection relies on a set of servers and measurements of the interacting players latencies. Measuring these latencies by actively probing the network is not scalable for a large number of players. We therefore explore the use of latency estimation techniques to gather this information.     

Frequent layer switching for perceived quality improvements of coarse-grained scalable video

Scalable video is an attractive option for adapting the bandwidth consumption of streaming video to the available bandwidth. Fine-grained scalability can adapt most closely to the available bandwidth, but this comes at the cost of a higher overhead compared to more coarse-grained videos. In the context of VoD streaming, we have therefore explored whether a similar adaptation to the available bandwidth can be achieved by performing layer switching in coarse-grained scalable videos. In this approach, enhancement layers of a video stream are switched on and off to achieve any desired longer term bandwidth. We have performed three user studies, two using mobile devices and one using an HDTV display, to evaluate the idea. In several cases, the far-from-obvious conclusion is that layer switching is a viable way of achieving bit-rate savings and fine-grained bit-rate adaptation even for rather short times between layer switches, but it does, however, depend on scaling dimensions, content and display device.     

Layer-encoded video streaming a proxy's perspective

This article describes a proxy's perspective in an architecture that supports efficient distribution of recorded video data in today's Internet. The support of layer-encoded video streaming with the aid of proxies enables a video distribution infrastructure that is efficient in today's Internet, and allows new mechanisms and techniques to be leveraged in a future Internet. An overview of a scalable and adaptive streaming architecture is presented. Open problems in the distribution and caching process are identified. Throughout the article solutions to improve the performance of such a video distribution architecture are discussed, mainly from the perspective of a proxy cache. The investigations that led to these solutions are based on an empirical experiment with layer encoded video. The goal of this experiment was to understand the effect of varying the number of layers on the viewer's perceived quality. The results of this initial investigation can be seen as the foundation for subsequent studies on mechanisms that improve the transport and caching of layer-encoded video in a scalable adaptive streaming architecture.     

Efficient disease detection in gastrointestinal videos – global features versus neural networks

Multimedia Tools and Applications - Analysis of medical videos from the human gastrointestinal (GI) tract for detection and localization of abnormalities like lesions and diseases requires both...     

The Nornir run-time system for parallel programs using Kahn process networks on multi-core machines—a flexible alternative to MapReduce

Even though shared-memory concurrency is a paradigm frequently used for developing parallel applications on small- and middle-sized machines, experience has shown that it is hard to use. This is largely caused by synchronization primitives which are low-level, inherently non-deterministic, and, consequently, non-intuitive to use. In this paper, we present the Nornir run-time system. Nornir is comparable to well-known frameworks such as MapReduce and Dryad that are recognized for their efficiency and simplicity. Unlike these frameworks, Nornir also supports process structures containing branches and cycles. Nornir is based on the formalism of Kahn process networks, which is a shared-nothing, message-passing model of concurrency. We deem this model a simple and deterministic alternative to shared-memory concurrency. Experiments with real and synthetic benchmarks on up to 8 CPUs show that performance in most cases scales almost linearly with the number of CPUs, when not limited by data dependencies. We also show that the modeling flexibility allows Nornir to outperform its MapReduce counterparts using well-known benchmarks.