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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2005.01.012 Byline: Michael SavoriA, Holger Karl, Morten Schlager, Tobias Poschwatta, Adam Wolisz Keywords: TCP; Congestion control; Network-information reuse; Common congestion control Abstract: Today's standard TCP implementations perform congestion control separately for each connection of an end system. It is advantageous in terms of overall performance, e.g., throughput and (short-term) fairness, to share network information between several TCP connections of an end system by establishing a common congestion control. In this paper, we present a new common congestion-control approach called "ensemble flow congestion management" (EFCM). First, we describe the design constraints of EFCM. Then, we explain and analyze the EFCM control algorithms. After that, we investigate the performance improvement of EFCM compared to standard TCP congestion control under different network conditions. Simulations with EFCM show a considerable increase in throughput and (short-term) fairness without increasing the aggressiveness of a set of TCP connections -- we also show this analytically using a fairness argument. The proposed EFCM controller algorithms are easy to implement and have a low additional complexity. Author Affiliation: Faculty of Electrical Engineering and Computer Science, Technical University of Berlin, Einsteinufer 25, 10587 Berlin, Germany Article History: Received 2 June 2004; Revised 7 January 2005; Accepted 12 January 2005 Article Note: (miscellaneous) Responsible Editor: G. Morabito

As we move from 5G to 6G, edge computing is one of the concepts that needs revisiting. Its core idea is still intriguing: Instead of sending all data and tasks from an end user's device to the cloud, possibly covering thousands of kilometers and introducing delays lower-bounded by propagation speed, edge servers deployed in close proximity to the user (e.g., at some base station) serve as proxy for the cloud. This is particularly interesting for upcoming machine-learning-based intelligent services, which require substantial computational and networking performance for continuous model training. However, this promising idea is hampered by the limited number of such edge servers. In this article, we discuss a way forward, namely the V-Edge concept. V-Edge helps bridge the gap between cloud, edge, and fog by virtualizing all available resources including the end users' devices and making these resources widely available. Thus, V-Edge acts as an enabler for novel microservices as well as cooperative computing solutions in next-generation networks. We introduce the general V-Edge architecture, and we characterize some of the key research challenges to overcome in order to enable wide-spread and intelligent edge services. [ABSTRACT FROM AUTHOR]

Assigning bands of the wireless spectrum as resources to users is a common problem in wireless networks. Typically, frequency bands were assumed to be available in a stable manner. Nevertheless, in recent scenarios where wireless networks may be deployed in unknown environments, spectrum competition is considered, making it uncertain whether a frequency band is available at all or at what quality. To fully exploit such resources with uncertain availability, the multi-armed bandit (MAB) method, a representative online learning technique, has been applied to design spectrum scheduling algorithms. This article surveys such proposals. We describe the following three aspects: how to model spectrum scheduling problems within the MAB framework, what the main thread is following which prevalent algorithms are designed, and how to evaluate algorithm performance and complexity. We also give some promising directions for future research in related fields. [ABSTRACT FROM AUTHOR]

NFV and SDN transform network management and operation into agile development tasks. They involve software artefacts, which are managed and deployed as composite services using DevOps principles. Those softwarized networks rely on complex technology stacks, starting with low-level virtualization technologies and ranging up to machine-learning-based orchestration solutions. One of the main challenges in those environments is to verify that the deployed functions and services operate correctly and meet the quality goals set by the stakeholders before they are put into production. We tackle this challenge by introducing the novel concept of a verification and validation (V&V) platform for NFV, which enables automatic testing and qualification of single network functions and complex services. By adding such a platform to the NFV ecosystem, new business models emerge, as we discuss in this article. We evaluate our proposed concepts by presenting a case study that uses our open source V&V platform to verify and validate the behavior and performance of a real-world network service. [ABSTRACT FROM AUTHOR]

To adapt to continuously changing workloads in networks, components of the running network services may need to be replicated (scaling the network service) and allocated to physical resources (placement) dynamically, also necessitating dynamic re-routing of flows between service components. In this paper, we propose joint optimization of scaling, placement, and routing (JASPER), a fully automated approach to jointly optimizing scaling, placement, and routing for complex network services, consisting of multiple (virtualized) components. JASPER handles multiple network services that share the same substrate network; services can be dynamically added or removed and dynamic workload changes are handled. Our approach lets service designers specify their services on a high level of abstraction using service templates. JASPER automatically makes scaling, placement and routing decisions, enabling quick reaction to changes. We formalize the problem, analyze its complexity, and develop two algorithms to solve it. Extensive empirical results show the applicability and effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Network function virtualization and software-defined networking allow services consisting of virtual network functions to be designed and implemented with great flexibility by facilitating automatic deployments, migrations, and reconfigurations for services and their components. For extended flexibility, we go beyond seeing services as a fixed chain of functions. We define the service structure in a flexible way that enables changing the order of functions in case the functionality of the service is not influenced by this and propose a YANG data model for expressing this flexibility. Flexible structures allow the network orchestration system to choose the optimal composition of service components that, for example, gives the best results for placement of services in the network. When number of flexible services and number of components in each service increase, combinatorial explosion limits the practical use of this flexibility. In this paper, we describe a selection heuristic that gives a Pareto set of the possible compositions of a service as well as possible combinations of different services, with respect to different optimization objectives. Moreover, we present a heuristic algorithm for placement of a combination of services, which aims at placing service components along shortest paths that have enough capacity for accommodating the services. By applying these solutions, we show that allowing flexibility in the service structure is feasible. [ABSTRACT FROM AUTHOR]

A current trend in networking and cloud computing is to provide compute resources at widely distributed sites; this is exemplified by developments such as network function virtualization. This paves the way for wide-area service deployments with improved service quality: e.g., user-perceived response times can be reduced by offering services at nearby sites. But always assigning users to the nearest site can be a bad decision if this site is already highly utilized. This paper formalizes two related decisions of allocating compute resources at different sites and assigning users to them with the goal of minimizing the response times while the total number of resources to be allocated is limited—a non-linear capacitated facility location problem with integrated queuing systems. To efficiently handle its non-linearity, we introduce five linear problem linearizations and adapt the currently best heuristic for a similar scenario to our scenario. All six approaches are compared in experiments for solution quality and solving time. Surprisingly, our best optimization formulation outperforms the heuristic in both time and quality. Additionally, we evaluate the influence of distributions of available compute resources in the network on the response time: the time was halved for some configurations. The presented formulation techniques for our problem linearizations are applicable to a broader optimization domain. [ABSTRACT FROM PUBLISHER]

The Service Programming and Orchestration for Virtualised Software Networks (SONATA) project targets both the flexible programmability of software networks and the optimisation of their deployments by means of integrating Development and Operations in order to accelerate industry adoption of software networks and reduce time-to-market for networked services. SONATA supports network function chaining and orchestration, making service platforms modular and easier to customise to the needs of different service providers, and introduces a specialised Development and Operations model for supporting developers. © 2016 The Authors. Transactions on Emerging Telecommunications Technologies Published by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Many electrical devices have a sleep mode to reduce their power consumption. However, changing into and out of the sleep mode delays processing and consumes power without performing useful work. Different strategies to activate the sleep mode allow different trade-offs between power consumption and latency. In this paper, we calculate which effects delayed activation and deactivation of a queueing system have on power consumption and latency. To this end, we created a Markov model as an abstraction of queuing systems with sleep modes and added delayed activation and deactivation. We analytically determined the steady state distribution of model states and give closed formulas for both power consumption and latency depending on the rate of arrival, processing, activation, deactivation, activation delay, and deactivation delay. We use this result to show that, surprisingly, cases exist in which adding both an activation delay and a deactivation delay reduces both mean power consumption and mean latency. Our simulation results demonstrate that this also holds for other random distributions. This shows that the opposing effects of activation delay and deactivation delay do not necessarily cancel each other out but can be used to reduce both power consumption and latency at the same time. [ABSTRACT FROM AUTHOR]

In wireless sensor networks (WSNs) energy efficiency and communication reliability are often conflicting requirements. Additionally, some application areas such as industrial automation or infrastructure monitoring impose strict latency bounds. Low-power receivers power consumption) together with adapted MAC protocols have the potential to meet these diverse requirements. We present an overview of state-of-the-art low-power receivers and relate their characteristics to requirements for different application areas. We compare low-power receivers to duty-cycled transceivers and present applications depending on them. For this, we use power consumption, sensitivity, and data rate as key performance figures for low-power receivers. Based on the characteristics of the applications we derive guidelines for using low-power receivers instead of ?duty-cycled transceivers. [ABSTRACT FROM PUBLISHER]

To solve the IP mobility problem, the use of multicast has been proposed in a number of different approaches, applying multicast in different characteristic ways. We provide a systematic discussion of fundamental options for multicast-based mobility support and the definition and experimental performance evaluation of selected schemes. The discussion is based on an analysis of the architectural, performance-related, and functional requirements. By using these requirements and selecting options regarding network architecture and multicast protocols, we identify promising combinations and derive four case studies for multicast-based mobility in IP-based cellular networks. These case studies include both the standard any-source IP multicast model as well as non-standard multicast models, which optimally utilize the underlying multicast. We describe network architecture and protocols as well as a flexible software environment that allows to easily implement these and other classes of mobility-supporting multicast protocols. Multicast schemes enable a high degree of flexibility for mobility mechanisms in order to meet the service quality required by the applications with minimal protocol overhead. We evaluate this overhead using our software environment by implementing prototypes and quantifying handoff-specific metrics, namely, handoff and paging latency, packet loss and duplication rates, as well as TCP goodput. The measurement results show that these multicast-based schemes improve handoff performance for high mobility in comparison to the reference cases: basic and hierarchical Mobile IP. Comparing the multicast-schemes among each other the performance for the evaluated metrics is very similar. As a result of the conceptual framework classification and our performance evaluations, we justify specific protocol mechanisms that utilize specific features of the multicast. Based on this justification, we advocate the usage of a source-specific multicast service model for multicast-based mobility support that adverts the weaknesses of the classical Internet any-source multicast service model. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents an end-to-end reservation protocol for quality-of-service (QoS) support in the medium access control layer of wireless multihop mesh networks. It reserves periodically repeating time slots for QoS-demanding applications, while retaining the distributed coordination function (DCF) for best effort applications. The key features of the new protocol, called "distributed end-to-end allocation of time slots for real-time traffic (DARE), are distributed setup, interference protection, and scheduling of real-time data packets, as well as the repair of broken reservations and the release of unused reservations. A simulation-based performance study compares the delay and throughput of DARE with those of DCF and the priority-based enhanced distributed channel access (EDCA) used in IEEE 802.11e. In contrast to DCF and EDCA, DARE has a low, nonvarying delay and a constant throughput for each reserved flow. [ABSTRACT FROM AUTHOR]

Quality models predict the perceptual quality of services as they calculate subjective ratings from measured parameters. In this article, we present a new quality model that evaluates Voice over IP (VoIP) telephone calls. In addition to packet loss rate, coding mode and delay, it takes into account the impairments due to changes in the transmission configuration (e.g. switching the coding mode or re-scheduling the playout time). Moreover, this model can be used at run time to control the transmission of such calls. It is also computationally efficient and open source. To demonstrate the potential of our model, we apply it to select the ideal coding and packet rate in bandwidth-limited environments. Furthermore, we decide, based on model predictions, whether to delay the playout of speech frames after delay spikes. Delay spikes often occur after congestion and cause packets to arrive too late. We show a considerable improvement in perceptual speech quality if our model is applied to control VoIP transmissions. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Within the last decade, the orthogonal frequency-division multiplexing (OFDM) transmission scheme has become part of several standards for wireless systems. Today, OFDM is even a candidate for fourth-generation wireless systems. It is well known that dynamic OFDMA systems potentially increase the spectral efficiency. They exploit diversity effects in time, space, and frequency by assigning system resources periodically to terminals. Informing the terminals about new assignments creates a signaling overhead. Up to now, this overhead has not been taken into account in studies on dynamic orthogonal frequency-division multiplexing access (OFDMA) systems. Yet this is crucial for a realistic notion of the performance achieved by dynamic approaches. In this paper, we close this gap. We introduce two forms of representing the signaling information and discuss how these affect system performance. The study of the signaling impact on the performance is conducted for an exemplary dynamic approach. We find that the throughput behavior of dynamic OFDMA systems is significantly influenced by the signaling overhead. In many situations, neglecting the overhead leads to wrong performance conclusions. Also, the performance difference between dynamic and static schemes is now much more sensible to the specific parameter set of the transmission scenario (e.g., frame length, subcarrier number, etc.). This leads to the proposal of access points which should adapt certain system parameters in order to provide optimal performance. [ABSTRACT FROM AUTHOR]

Java, in combination with Web browsers' abilities to load and execute untrusted Java applets in a secure fashion, has made computing over the Web a possibility. Now the challenge is to fully utilize this potential, given the limitations imposed by browsers. This paper presents KnittingFactory, an infrastructure to facilitate Web-based computing, which addresses this challenge. It supports building distributed applications, specifically those consisting of Java applets executing in browsers. It is composed of: (i) a distributed name service to assist users in locating other participants of a distributed computation via standard browsers; (ii) an embedded class server to eliminate the need for external HTTP servers for serving applet code; and (iii) a technique for direct applet-to-applet communication. In this paper, we describe the design and implementation of KnittingFactory and demonstrate its benefits by applying it to three distinct areas of Web-based computing. First, we apply our distributed name service to a client/server architecture to enable RMI clients to locate servers on unknown hosts. Second, we use the embedded class server to extend the capability of Charlotte, a parallel computing environment. Finally, we build a collaborative application using our direct applet-to-applet communication technique which does not require a forwarding agent. © 1998 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Using Java for high-performance distributed computing aggravates a well-known problem: the choice between efficient message-passing environments and more convenient distributed shared memory systems which often provide additional functionalities like adaptive parallelism or fault tolerance – with the latter being imperative for Web-based computing. This paper proposes an extension to the DSM-based Charlotte system that incorporates advantages from both approaches. Annotations are used to describe the data dependencies of parallel routines. With this information, the runtime system can improve the communication efficiency while still guaranteeing the correctness of the shared memory semantics. If the correctness of these annotations can be relied upon, additional optimizations are possible, ultimately sharing primitive data types such as int across a network, making the overhead associated with accessing and sharing objects unnecessary. In this case, the annotations can be regarded as a compact representation of message-passing semantics. Thus, a program's efficiency can be improved by step-by-step incorporation of semantic knowledge. The possibility to freely mix and to easily switch between unannotated code, annotated code and shared primitive data types entails a big flexibility for the programmer. A number of measurements show significant performance improvements for annotations and annotation-based shared primitive types. © 1998 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Summary: Softwarized networks are the key enabler for elastic, on‐demand service deployments of virtualized network functions. They allow to dynamically steer traffic through the network when new network functions are instantiated, or old ones are terminated. These scenarios become in particular challenging when stateful functions are involved, necessitating state management solutions to migrate state between the functions. The problem with existing solutions is that they typically embrace state migration and flow rerouting jointly, imposing a huge set of requirements on the on‐boarded virtualized network functions (VNFs), eg, solution‐specific state management interfaces. To change this, we introduce the seamless handover protocol (SHarP). An easy‐to‐use, loss‐less, and order‐preserving flow rerouting mechanism that is not fixed to a single state management approach. Using SHarP, VNF vendors are empowered to implement or use the state management solution of their choice. SHarP supports these solutions with additional information when flows are migrated. In this paper, we present SHarP's design, its open source prototype implementation, and show how SHarP significantly reduces the buffer usage at a central (SDN) controller, which is a typical bottleneck in state‐of‐the‐art solutions. Our experiments show that SHarP uses a constant amount of controller buffer, irrespective of the time taken to migrate the VNF state. [ABSTRACT FROM AUTHOR]

Interference is one of the most challenging problems in current cellular mobile access networks. Coordinated nultipoint transmission/ reception, and in particular joint processing, has proven to be a beneficial solution for interference management. Most research so far has investigated the requirements and gains on the wireless side but only superficially showed the impact on and requirements for the backhaul network. We take a different approach by looking at different backhaul topologies and technologies, and analyzing how they can support CoMP cooperation schemes. We study, for different traffic scenarios and backhaul connectivity levels, which base station clusters are actually feasible compared to the ones desirable from the radio access network perspective. We found out that a significant mismatch exists between the desired wireless clusters, as defined by the RAN, and feasible ones, as allowed by the given backhaul characteristics. Based on these findings, we explain how RAN clustering and backhaul clustering have to cooperate to come to feasible solutions. As one possible solution, we present a backhaul network preclustering scheme, which is able to predict which BSs are actually eligible for cooperation during the runtime of the network. The gains of this approach are quantifiable in terms of reduced signaling and user data exchange, and reduced MIMO signal processing. [ABSTRACT FROM AUTHOR]

A new network architecture for the Internet needs ingredients from three approaches: information- centric networking, cloud computing integrated with networking, and open connectivity. Information-centric networking considers pieces of information as first-class entities of a networking architecture, rather than only indirectly identifying and manipulating them via a node hosting that information; this way, information becomes independent from the devices they are stored in, enabling efficient and application- independent information caching in the network. Cloud networking offers a combination and integration of cloud computing and virtual networking. It is a solution that distributes the benefits of cloud computing more deeply into the network, and provides a tighter integration of virtualization features at computing and networking levels. To support these concepts, open connectivity services need to provide advanced transport and networking mechanisms, making use of network and path diversity (even leveraging direct optical paths) and encoding techniques, and dealing with ubiquitous mobility of user, content and information objects in a unified way. [ABSTRACT FROM PUBLISHER]