Context:There have been numerous recent calls for research on the human side of software engineering and its impact on various factors such as productivity, developer happiness and project success. An analysis of which challenges in software engineering teams are most frequent is still missing. As teams are more international, it is more frequent that their members have different human values as well as different communication habits. Additionally, virtual team setups (working geographically separated, remote communication using digital tools and frequently changing team members) are increasingly prevalent.Objective:We aim to provide a starting point for a theory about contemporary human challenges in teams and their causes in software engineering. To do so, we look to establish a reusable set of challenges and start out by investigating the effect of team virtualization. Virtual teams often use digital communication and consist of members with different nationalities that may have more divergent human values due to cultural differences compared to single nationality teams.Method:We designed a survey instrument and asked respondents to assess the frequency and criticality of a set of challenges, separated in context ”within teams” as well as ”between teams and clients”, compiled from previous empirical work, blog posts, and pilot survey feedback. For the team challenges, we asked if mitigation measures were already in place to tackle the challenge. Respondents were also asked to provide information about their team setup. The survey included the Personal Value Questionnaire to measure Schwartz human values. Finally, respondents were asked if there were additional challenges at their workplace. The survey was first piloted and then distributed to professionals working in software engineering teams via social networking sites and personal business networks.Result:In this article, we report on the results obtained from 192 respondents. We present a set of challenges that takes the survey feedback into account and introduce two categories of challenges; ”interpersonal” and ”intrapersonal”. We found no evidence for links between human values and challenges. We found some significant links between the number of distinct nationalities in a team and certain challenges, with less frequent and critical challenges occurring if 2-3 different nationalities were present compared to a team having members of just one nationality or more than three. A higher degree of virtualization seems to increase the frequency of some human challenges, which warrants further research about how to improve working processes when teams work from remote or in a distributed fashion.Conclusion:We present a set of human challenges in software engineering that can be used for further research on causes and mitigation measures, which serves as our starting point for a theory about causes of contemporary human challenges in software engineering teams. We report on evidence that a higher degree of virtualization of teams leads to an increase of certain challenges. This warrants further research to gather more evidence and test countermeasures, such as whether the employment of virtual reality software incorporating facial expressions and movements can help establish a less detached way of communication.

With the rapid growth of user traffic, service innovation, and the persistent necessity to reduce costs, today's mobile operators are faced with several challenges. In networking, two concepts have emerged aiming at cost reduction, increase of network scalability and deployment flexibility, namely Network Functions Virtualization (NFV) and Software Defined Networking (SDN). NFV mitigates the dependency on hardware, where mobile network functions are deployed as software virtual network functions on commodity servers at cloud infrastructure, i.e., data centers. SDN provides a programmable and flexible network control by decoupling the mobile network functions into control plane and data plane functions. The design of the next generation mobile network (5G) requires new planning and dimensioning models to achieve a cost optimal design that supports a wide range of traffic demands. We propose three optimization models that aim at minimizing the network load cost as well as data center resources cost by finding the optimal placement of the data centers as well the SDN and NFV mobile network functions. The optimization solutions demonstrate the trade-offs between the different data center deployments, i.e., centralized or distributed, and the different cost factors, i.e., optimal network load cost or data center resources cost. We propose a Pareto optimal multi-objective model that achieves a balance between network and data center cost. Additionally, we use prior inference, based on the solutions of the single objectives, to pre-select data center locations for the multi-objective model that results in reducing the optimization complexity and achieves savings in run time while keeping a minimal optimality gap.

Hybrid IP networks that use both control paradigms - distributed and centralized - promise the best of two worlds: 1) programmability of software-defined networking (SDN) and 2) reliability and fault tolerance of distributed routing protocols, like open shortest path first (OSPF). Typically, a hybrid network deploys SDN to control prioritized traffic and OSPF to assure care-free operation of best effort traffic. We propose a new hybrid network architecture, called SDN partitioning (SDNp), which establishes centralized control over the distributed routing protocol by partitioning the topology into sub-domains with SDN-enabled border nodes. In our approach, OSPF's routing updates have to traverse SDN border nodes to reach neighboring sub-domains. This allows the central controller to modify how sub-domains view one another, which in turn allows to steer inter-sub-domain traffic. The degree of dynamic control against simplicity of OSPF can be traded off by adjusting the size of the sub-domains. This paper studies the technical requirements, presents a novel scheme for balanced topology partitioning, and provides the corresponding network management models for SDNp. Our performance evaluation shows that - already in its minimum configuration with two sub-domains - SDNp provides significant improvements in all respects compared to legacy routing protocols, whereas smaller sub-domains provide network control capabilities comparable to full SDN deployment.

As the Software Defined Networking (SDN) paradigm gains momentum, network operators wonder about how to go about replacing their legacy IP routers with SDN-compliant ones. While forklift network upgrades are impractical in operational networks, the promise of SDN is too compelling. Thus, a viable solution is to gradually migrate over time, leading to hybrid OSPF/SDN networks. Although recent studies proposed device architectures, protocols and algorithms required in such hybrid networks, a single routing domain's SDN migration trajectory - as a whole - has hardly been studied. Significance of the sequence in which IP routers are replaced with SDN routers and optimal sequence of router replacements need to be investigated. In this paper, we address these questions based on SDN's traffic engineering (TE) gains and an operator's SDN investment constraints. We propose optimization techniques and heuristics to plan an effective migration schedule in a single routing domain and demonstrate the significance of such a schedule using relevant network management metrics. Our results suggest: (a) the sequence of IP routers migrating to SDN largely determine the resulting TE gains, and, (b) to determine the best migration sequence, novel greedy algorithms perform almost as good as optimization techniques.

Software Defined Networking (SDN) marks a paradigm shift towards an externalized and logically centralized network control plane. A particularly important task in SDN architectures is that of controller placement, i.e., the positioning of a limited number of resources within a network to meet various requirements. These requirements range from latency constraints to failure tolerance and load balancing. In most scenarios, at least some of these objectives are competing, thus no single best placement is available and decision makers need to find a balanced trade-off. This work presents POCO, a framework for Pareto-based Optimal COntroller placement that provides operators with Pareto optimal placements with respect to different performance metrics. In its default configuration, POCO performs an exhaustive evaluation of all possible placements. While this is practically feasible for small and medium sized networks, realistic time and resource constraints call for an alternative in the context of large scale networks or dynamic networks whose properties change over time. For these scenarios, the POCO toolset is extended by a heuristic approach that is less accurate, but yields faster computation times. An evaluation of this heuristic is performed on a collection of real world network topologies from the Internet Topology Zoo. Utilizing a measure for quantifying the error introduced by the heuristic approach allows an analysis of the resulting trade-off between time and accuracy. Additionally, the proposed methods can be extended to solve similar virtual functions placement problems which appear in the context of Network Functions Virtualization (NFV).

Given the assumption that network equipment vendors will soon deploy new energy saving mechanisms in their routers, the question we are aiming to answer is this: Where in the network to start the migration to energy efficient routers, and how large is the impact of the migration scheduling on the total energy saving? To this end, the paper studies a scenario where network nodes can reduce the power consumption proportional to the router traffic load, and elaborates on the impact of the migration node sequence that determines at which point in time which node migrates. While every router can gradually increase and decrease the consumption based on load, at the same time, the network as a whole is subject to a gradual migration on its own, where energy efficient network routers are installed over multiple planning periods. Our results show that an increase of saved energy up to 12 percentage points is possible only by changing the migration sequence of energy efficient routers. Additionally, we show that deploying mechanisms of Traffic Engineering can further significantly improve the overall energy savings especially during the early stages of migration.

No abstract available.

In this paper, we analyze the question of network migration to Software Defined Networking (SDN) from the perspective of Traffic Engineering (TE). For a given network topology and migration planning horizon, we ask the question of which routers in the IP network should migrate to SDN-enabled operation to reduce the need for network capacity upgrades over a given time horizon. We propose an algorithm to determine the optimum schedule for node substitution within a network, which shows that already a few SDN routers, when strategically located, provide a stably large number of path alternatives to be used in TE, thus substantially reducing the need for large network capacity upgrades.

Network virtualization is seen as a possible solution to the ossification problem of the Internet by providing flexible and scalable virtual networks running over heterogeneous physical infrastructure. As for today's networks, it is very crucial to evaluate the virtual networks' adaptability to fulfill the demanding quality requirements of the diverse service offers. In addition, such an environment should promote protection strategies to face the unpredictable network failures, which cause significant service interruptions and consequently lead to definite revenue losses. Therefore, we introduce Quality of Service (QoS) modeling in virtual networks and provide three novel QoS-aware, resilient and cost-optimal virtual network design solutions. Through comprehensive simulations we show the necessity for such QoS models in virtual networks, where a no-QoS model fails to meet the requirements of 76% of the services for some service distributions. Finally, we compare the performance of the three proposed solutions having QoS-guarantees and resilience at different virtualization layers and show that there is a trade-off between virtual network cost and network utilization.

Conventionally, network migration models study competition between emerging and incumbent technologies by considering the revenue increase and migration cost. We propose to extend the existing network migration models with new critical factors, including (i) synergistic relationships across multiple technologies, (ii) reduction in operation expenditures (OpEx), and, (iii) effect of social factors on human decisions. To this end, we propose a novel agent-based migration model considering these factors. Based on the model, we analyze the case study of optimal path computation with joint migration to two emerging networking paradigms, i.e., IETF Path Computation Element (PCE) and Software-Defined Networking (SDN). Our results demonstrate the synergistic effects of migration to multiple complementary technologies, and shows that a technology migration may be eased by the joint migration to multiple technologies.

Ethernet's success in local area networks (LANs) is fueling the efforts to extend its reach to cover metro and long-haul networks. This new Ethernet is refereed to as Carrier Ethernet. Among the various transport infrastructures for realizing Carrier Ethernet, wavelength-division multiplexing (WDM) optical network is a strong candidate for this purpose. Optical transmission rates per channel are increasing from 10 to 40 Gb/s and even 100 Gb/s, and they can also coexist in the same fiber. Along with the flexibility associated with such a network with mixed-line rates (MLR), signal-related constraints at high rates become a challenge for cost-efficient routing. Among these issues is the maximum nonregenerated optical distance that a signal can travel before its quality degrades or maximum transmission range (TR). TR is rate-dependent: The higher the rate, the shorter the range. While high-rate pipes may require signal regeneration to restore the signal's quality, they support more traffic and, hence, can save resources. We study the problem of cost-efficient routing of multi-bit-rate (1/10/40/100 Gb/s) Ethernet tunnels using MLR over a carrier's WDM optical network with signal-transmission-range constraints. We studied the effect of TR for mixed-rate signals (10/40/100 Gb/s) on the network's cost to determine the optimal TR of each bit rate. We present an analytical model based on a mixed-integer linear program (MILP) to determine the optimal TR of a small network. Since MILP has scalability constraints that makes it hard or sometimes impossible to solve for real network topologies, we propose a graph-based solution that constructs a mixed-line-rate auxiliary (MLR-AUX) graph to capture the network's heterogeneity and a weight-assignment approach that allows the routing to be cost-efficient. Our algorithms were tested on a U.S. nationwide network topology. We found that it is possible to reduce the network's cost by using short TR and that the optimal TR depends strongly on traffic characteristics and on the TR values of different bit-rate signals.

Ethernet is a success story in Local Area Networks (LAN). Efforts for extending its boundaries beyond LAN to the carriers' backbone networks are in progress. We study the problem of designing reliable and cost-efficient high-rate (100 Gbit/s) carrier-grade Ethernet in a multi-line-rate telecom network under signal transmission-range constraints. Reliability is achieved using shared-path protection at two levels: (1) Protection-at-Connection (PAC) level, or (2) Protection-at-Lightpath (PAL) level. We study the two cases for their impact on network cost and other performance parameters. We construct a graph, called Mixed Topology (MT), using which it is possible to: (1) identify traffic grooming possibilities, (2) select a path which requires the minimum amount of 3R regeneration, and (3) effectively choose the data rate of a lightpath to be established. Our algorithms, tested on the 17-node German network, lead to the following findings: (1) for both PAL and PAC, our MT-based algorithm resulted in lower network cost and higher lightpath utilization compared with other schemes; and (2) in general, PAL incurs slightly higher cost than PAC.