Dieter Stoll

A case study in root cause defect analysis

There are three interdependent factors that drive our software development processes: interval, quality and cost. As market pressures continue to demand new features ever more rapidly, the challenge is to meet those demands while increasing, or at least not sacrificing, quality. One advantage of defect prevention as an upstream quality improvement practice is the beneficial effect it can have on interval: higher quality early in the process results in fewer defects to be found and repaired in the later parts of the process, thus causing an indirect interval reduction. We report a retrospective root cause defect analysis study of the defect Modification Requests (MRs) discovered while building, testing, and deploying a release of a transmission network element product. We subsequently introduced this analysis methodology into new development projects as an in-process measurement collection requirement for each major defect MR. We present the experimental design of our case study discussing the novel approach we have taken to defect and root cause classification and the mechanisms we have used for randomly selecting the MRs to analyze and collecting the analyses via a Web interface. We then present the results of our analyses of the MRs and describe the defects and root causes that we found, and delineate the countermeasures created to either prevent those defects and their root causes or detect them at the earliest possible point in the development process. We conclude with lessons learned from the case study and resulting ongoing improvement activities.

Classification and evaluation of defects in a project retrospective

There are three interdependent factors that drive our development processes: interval, quality and cost. As market pressures continue to demand new features ever more rapidly, the challenge is to meet those demands while increasing, or at least not sacrificing, quality. One advantage of defect prevention as an upstream quality improvement practice is the beneficial effect it can have on interval: higher quality early in the process results in fewer defects to be found and repaired in the later parts of the process, thus causing an indirect interval reduction.We report a retrospective analysis of the defect modification requests (MRs) discovered while building, testing, and deploying a release of a network element as part of an optical transmission network. The study consists of three investigations: a root-cause defect analysis (RCA) study, a process metric study, and a code complexity investigation. Differing in the quantities that we anticipate to be related to found defects, they all have in common the goal of identifying early quality indicators.The core of this threefold study is the root-cause analysis. We present the experimental design of this case study in some detail and its integration into the development process. We discuss the novel approach we have taken to defect and root cause classification and the mechanisms we have used for randomly selecting the MRs, to analyze and collecting the analyses via a web interface. We present the results of our analyses of the MRs and describe the defects and root causes that we found, and delineate the countermeasures created either to prevent those defects and their root causes or to detect them at the earliest possible point in the development process. We conclude the report on the root-cause analysis with lessons learned from the case study and from our experiences during subsequent usage of this analysis methodology for in-process measurement.Beyond the root-cause analysis, we first present our findings on the correlation between defects detected and the adherence to our development process. Second, we report on our experience with analyzing static code properties and their relation to observed defect numbers and defect densities.

Ethernet aggregation and core network models for efficient and reliable IPTV services

With the growing interest on wireline network architectures for residential triple-play and business Ethernet services there is a renewed demand for efficient and reliable packet-based transport capabilities between the content providers and the end users. Voice and data traffic carried over a variety of access technologies is collected via technology-specific access networks (e.g., digital subscriber line [xDSL], passive optical network [xPON], and wireless fidelity [WiFi]). Metro and core networks need to aggregate the various user flows from different access network nodes and provide scalable and cost-effective distribution of various flow types (e.g., Internet access, voice, video on demand, and broadcast TV services) to the relevant service access points. Varying quality of service and resiliency requirements for these services are being reflected in a new breed of converged Ethernet and optical network elements with capabilities to interwork the bearer-planes of these two networking technologies seamlessly. Network elements based on Ethernet/Optical converged technology are able to select the most fitting mechanisms from each networking technology to meet the transport requirements for each individual service demand better while providing significantly enhanced implementation and operational efficiencies. This paper discusses network architecture models and network elements addressing these goals.

The role of pseudo-wires for layer 2 services in intelligent transport networks

Pseudo-wire emulation edge-to-edge over multiprotocol label switching (MPLS) is a promising technology for layer 2 transparent service support in metro networks. It supports Ethernet private line applications such as virtual private wire services (VPWS), multipoint local area network (LAN) applications such as virtual private LAN services (VPLS), frame relay, asynchronous transfer mode (ATM), and even the emulation of time division multiplexing (TDM) services. In the case of Ethernet, this technology circumvents the disadvantages of native Ethernet-based services, such as the need for spanning trees. In combination with traffic engineered label-switched paths (LSPs), it promises support for quality of service (QoS) differentiation and traffic engineering for high-value business services. MPLS is currently viewed as the technology that could satisfy this need, but because it serves so many other purposes as well, it entails complex control plane protocols and relatively high cost. This is in opposition to operator demand for low capital expenditure (CAPEX) and operational expenditure (OPEX) cost when introducing new services. This paper presents an analysis of how TDM-based transport networks can evolve, maximizing the benefit of established transport technologies, while supporting existing layer 2 transport services as well as new services such as Internet Protocol television (IPTV) and video on demand. The paper identifies which of the mechanisms that are underlying MPLS-based pseudo-wire services are truly essential, and which could be implemented by other means and thus offer new possibilities for migration and convergence. Besides conceptual considerations, the network efficiency of alternative implementation options is analyzed and compared.