Kristian Nybom

DevOps: A Definition and Perceived Adoption Impediments

As the interest in DevOps continues to grow, there is an increasing need for software organizations to understand how to adopt it successfully. This study has as objective to clarify the concept and provide insight into existing challenges of adopting DevOps. First, the existing literature is reviewed. A definition of DevOps is then formed based on the literature by breaking down the concept into its defining characteristics. We interview 13 subjects in a software company adopting DevOps and, finally, we present 11 impediments for the company’s DevOps adoption that were identified based on the interviews.

Unequal error protection for data partitioned H.264/AVC video broadcasting

Application Layer Forward Error Correction (AL-FEC) is becoming a popular addition to protocols for real-time video delivery over IP-based wireless networks. In particular, rateless codes are identified as suitable solution for AL-FEC due to their flexibility and capacity-approaching performance. Since each part of video data is not equally important for video reconstruction, it is beneficial to group it based on its importance, and then provide different degree of protection using Unequal Error Protection (UEP). Data partitioning (DP) is one such low-cost feature in H.264/AVC enabling partitioning of video data based on its importance. We propose schemes for the DP H.264/AVC video transmission using Raptor and Random Linear Codes (RLC) and investigate their performance as AL-FEC solutions in Digital Video Broadcasting. We provide comparisons between optimized Non-Overlapping Window RLC and Expanding Window (EW) RLC, which are two effective UEP RLC strategies. The results using realistic channel traces show viability of the EW RLC as a promising solution for multimedia broadcast applications.

Expanding Window Fountain coded scalable video in broadcasting

The Expanding Window Fountain (EWF) codes are a new class of rateless codes, providing Unequal Error Protection (UEP). These codes are especially suitable for Scalable Video Coding (SVC) having unequally important data layers. In this paper, we show that EWF codes are usable for transmitting scalable video in mobile channels. We characterize the channel by field measurements in a DVB-H network. We tune the EWF code parameters to achieve real-time transmissions of SVC video. Moreover, we use a code symbol header for the EWF codes, which is also used in the IPDC over DVB-H standard, such that the codes can be efficiently used without the need for excessive packet header redundancy. We show that if some latency in the video is acceptable, then EWF codes can be used for real-time transmissions.

Distributed Spectrum Sensing Using Low Cost Hardware

A distributed spectrum sensing network is prototyped using off the shelf hardware consisting of Raspberry Pi mini-computers and DVB-T receivers with software defined radio capabilities. Using the prototype network, coordinated, distributed wideband spectrum sensing is performed in a geographical area. The spectrum sensing data from the nodes is collected in a database. Well established low-complexity algorithms for distributed spectrum sensing are applied, and the results are compared against a professional spectrum sensing system. We show that with this simple low-cost setup, the decisions made on the availability of spectrum using the distributed sensing data correspond well with the decisions made on the reference data.

Scalable video coding for mobile broadcasting DVB systems

H.264 Scalable Video Coding (SVC) is an extension to the Advanced Video Coding (AVC) H.264 standard which provides efficient scalability functionalities on top of the high coding efficiency of H.264/AVC. SVC allows for temporal, spatial, and quality scalability of the output video stream, encoding the video information into an H.264/AVC base layer and a series of enhancement layers which incrementally improve the quality, increase screen resolution and/or frame rate. SVC is particularly suited for mobile TV reception, since the received video quality is adaptable to variable reception conditions and heterogeneous receiver capabilities. However, mobile TV Digital Video Broadcasting (DVB) standards such as DVB-H and DVB-SH were designed prior to the introduction of SVC, and therefore the underlying transmission protocols are not optimized for scalable video delivery. In this overview paper, we review recently proposed solutions for SVC stream adaptation on the underlying DVB-H/SH protocols, and point out novel technical solutions that are currently under consideration for the next generation mobile broadcasting standard DVB-NGH.

Sparse-graph AL-FEC solutions for IP datacasting in DVB-H

DVB-H is an IP-based wireless broadcast technology in which users are offered, among other services, the IP datacast (IPDC) service for downloading broadcasted files to their mobile terminals. In this paper, we explore different AL-FEC solutions providing simple and efficient file delivery. Our investigation is focused on recently popular classes and design methods of sparse-graph codes decoded using the iterative decoding algorithm. We provide performance comparisons of various possible AL-FEC schemes in a simulated DVB-H environment. The benefits and drawbacks of different sparse-graph AL-FEC solutions are discussed.

Designing Tornado Codes as Hyper Codes for Improved Error Correcting Performance

Digital services are increasingly being delivered to user terminals over wireless multicast networks. When the target service requires uncorrupted data delivery, there is an increasing need for developing techniques for reliable content delivery. In multicast networks, the typical way of providing reliable content delivery is to apply forward error correcting techniques (FEC). In this paper, we introduce a modification to the Tornado code, where we combine the structures of Tornado codes and Hyper codes. Standard Tornado codes have the drawback that they are dependent on the error distribution on the data path. By combining the Tornado code with a Hyper code, we decrease the probability of the Tornado decoder failing due to inopportune error distribution in the source data. We demonstrate, based on a simulated transmission channel, that the error correcting performance is improved, at the cost of slightly longer decoding times, by using a combination of Hyper codes and Tornado codes, compared to the standard Tornado codes.

On the Impact of Mixing Responsibilities Between Devs and Ops

Many software engineering organizations around the world are adopting DevOps. One of the goals of DevOps is to foster better collaboration between development and operations personnel, in order to improve organizational efficiency. Since DevOps is lacking a common definition, there are several approaches to adopt it, and organizations largely need to determine how to apply DevOps for themselves. In this paper, we present results from a case study in which a software organization adopts DevOps. The focus of this research is to study the impact of mixing the responsibilities between development and operations engineers. We interviewed 14 employees in the organization during the study, and results indicate several benefits of the chosen approach, such as improved collaboration and trust, and smoother work flow. This comes at the cost of a number of complications, such as new sources for friction among the employees, risk for holistically sub-optimal service configurations, and more.

Receiver Coding Gain in DVB-H Terminals Using Application Layer FEC Codes

DVB-H is targeted for broadcasting digital content to handheld devices. The content is generally divided into streaming media or file downloading. In file downloading scenarios there is typically a requirement on a zero error ratio which can be met using either a data carousel or additional forward error correction codes. Both methods however induce a higher energy consumption in the receiver. This paper analyses the energy consumption needed for two different forward error correction codes based on emulator results for typical hardware in a handheld device. The energy used for error correction is compared to the energy used when receiving more carousel rounds in order to meet the zero error ratio requirement. This difference is denoted as receiver coding gain. Additionally, error correction also leads to a reduction in the reception time.

Improving Object Delivery Using Application Layer Tornado Codes in DVB-H Systems

This paper analyzes the effects of applying application layer forward error correcting (FEC) coding to a wireless filecasting system, here represented by DVB-H. We show the benefit of moving error correcting coding to higher levels in the data transmission protocol stack. The data is delivered using a data carousel and the FEC code utilized is a hyper-Tornado code for which the main characteristics are long codewords and near linear complexity. Because the hyper-Tornado code provides internal data interleaving and supports long code lengths, we can observe a significantly decreased number of mean data carousel iterations before an error-free carousel object is received compared to the basic DVB-H system. This reduction is for the user observed as decreased download-time, but also provides energy saving in the receiver due to shorter receiver on-times