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A combined hybrid automatic repeat request (ARQ) error control and adaptive scheduling scheme is proposed for time-division multiple access/time-division duplex medium access control (MAC) protocols in wireless asynchronous transfer mode (ATM) networks. Specifically, with the aid of proper channel modeling, the performance of various error-control schemes is evaluated. Accordingly, type-II hybrid ARQ is chosen as the error recovery scheme to combat fading effects, while adaptive fair-queueing is designed to achieve a fair and efficient resource allocation in wireless channels. In particular, the weight of a connection used in the fair-queueing algorithm dynamically adapts in terms of varying channel conditions and the types of services. Various simulations are conducted in typical indoor wireless ATM networks. It is shown that the proposed scheme can achieve a high throughput and transfer reliability with minimized delay and cell loss rate when compared with the conventional MAC layer control.

Die Verbreitung ortsbezogener Dienste bedroht die Privatsphäre der Benutzer in einer neuen Weise. Das Bilden eines hochgenauen Profils der Ortsinformation lässt häufig Rückschlüsse auf aktuelle Tätigkeit und Vorlieben eines Benutzers zu. Da die entsprechenden Dienste zur Erbringung ihrer Funktionalität auf die Verfügbarkeit genauer Ortsinformation angewiesen sind, muss der Benutzer in der Lage sein, den Zugriff auf diese Information nach seinen Bedürfnissen zu erlauben bzw. einzuschränken. Darüber hinaus darf es nicht möglich sein, ohne seine Zustimmung die Ortsinformation mit seiner Identität zu verknüpfen. In diesem Artikel wird nach einer kurzen Einführung auf die Datenhaltung hochgenauer Ortsinformation sowie die damit verbundene Sicherheitsproblematik eingegangen. Danach werden Möglichkeiten zum Schutz sowohl der Ortsinformation als auch der Identitätsinformation aufgezeigt und abschließend diskutiert.

Content delivery networks have been widely used for many years providing service for millions of users. Lately, many of these networks are migrating to the cloud for its numerous advantages such as lower costs, increased performance, availability and flexibility in installing new resources. This paper introduces a new approach towards load balancing as well as power reduction in cloud-based content delivery networks allowing for a controlled scaling of operational parameters within the tradeoff between power consumption and quality of experience (QoE). By applying a new proposed adaptive server activation/ deactivation model at each data center in the cloud, unutilized servers at the data center can be switched off to reduce the power consumption. This adaptive model also allows the data center to maintain its performance while being utilized up to 95%. Performance measures of data centers are crucial as there are certain user service level agreements (SLA) for the cloud subscribers that should not be violated; most important is the latency for users' requests. The proposed load balancing algorithm benefits from limited latency for requests by only shifting the load off a data center when it is almost fully loaded. When the load in a data center exceeds a critical level, processes are migrated to underloaded data centers within the cloud. The self-controlled adaptive resource management supports easing of the cloud management.

Sleep modes are important for user equipment to reduce power consumption or to reduce battery reloading. To keep the user equipment connected, it has to be activated for uplink or downlink data transfer which causes overhead and additional delay. Wireless or mobile equipment has to be monitored repeatedly for location updates. These classes of problems can be modeled by queuing systems with modified busy and idle periods. In this paper, we consider a generalized infinite-buffer, single-server queuing systems with activation overhead and under various types of sleep modes during inactive periods. For the special assumption of Markovian arrival processes of data units and generally distributed activation times and vacation (sleep) periods, the models can be analyzed exactly by a mean value analysis method which is based on regenerative stochastic processes, renewal theory and classical queuing theorems. The method allows also for dynamic sleep periods which are dependent on each other as in the case of the standard IEEE 802.16m for wireless equipment. Explicit results are derived for average values of data unit delays, resource utilization and power- saving margins dependent on given parameters for activation times and wakeup signaling frequencies. The models include the special cases of M/G/1 queuing systems with a modified service time of the first arrival initiating a busy period and M/G/1 queuing systems with vacation periods, respectively, which are well known from literature providing general solutions for the state and delay distributions. Finally, all models are extended to the exact analysis of Batch Poisson arrival processes.

Im vorliegenden Beitrag wurde der Versuch unternommen, Rechnersysteme mit Multiprogramming und Paging einschlieslich der auf ihnen ablaufenden Programme durch Modelle zu beschreiben. Aufbauend auf Modellkriterien fur Rechnersysteme mit einer zweistufigen Speicherhierarchie, fur Programmverhalten und Betriebssystemstrategien wurde ein verfeinertes Modell entwickelt und mit Hilfe der Simulation untersucht. Ausserdem wurde eine mathematische Analyse fur vereinfachte Warteschlangenmodelle vorgenommen. Die Ergebnisse zeigen den prinzipiellen Einflus der einzelnen Modellparameter auf die Leistungsfahigkeit derartiger Rechnersysteme. Der Vergleich zwischen Simulation und Rechnung ergibt, das die prinzipiellen Charakteristika wie Auslastungen, Durchsatz und Durchlaufzeiten relativ genau mit Hilfe von Warteschlangenmodellen abgeschatzt werden konnen. Genauere Aufschlusse z.B. uber die Einflusse des Lokalitatsverhaltens von Programmen sowie der Ersetzungs-strategien im Zusammenspiel mit den anderen Systemkomponenten konnen jedoch nur mit Hilfe der Simulation gewonnen werden.

Communication Networks migrate towards an infrastructure, which ischaracterized by seamless interoperation of heterogeneous subnetworks with different protocol architectures, network technologies, and services. The user will not be aware of this heterogeneity, but relies on a secure, reliable and efficient operation supporting his applications. To provide such a quality of service, communication networks have to meet stringent quality requirements with respect to

The Broadband-ISDN allows the integration of arbitrary type traffic such as voice, video, image and data with constant or variable bitrates. B-ISDN is based on the Asynchronous Transfer Mode (ATM), by which small packets of constant size (cells) are multiplexed, switched and transmitted on the basis of an established virtual connection. The favorable technique is flexible to accept a variety of services differing in source traffic characteristics. The ATM technique causes, however, a set of serious traffic control and grade of service problems which have to be mastered before such networks are put into operation. Thus, worldwide activities on that subject can be observed.

This work yields a generic modelling approach for the signalling load as a result of the various communications services, especially new services like UPT. A tool has been developed which provides the distinct loading of all hard- and software signalling network resources and on which a hierarchical performance analysis and planning procedures are based. The results of the analysis are used to evaluate the end-to- end performance of the call scenarios under consideration. A numerical example, including ISDN and PLMN scenarios, outlines the application of the tool to a hypothetical network.

Communication architectures with a multi-layer protocol structure are extremely difficult to evaluate due to the model complexity. In this paper, a hierarchical decomposition and aggregation technique is described which is oriented at the ISO Basic Reference Model. In particular, connection-oriented and connectionless data transmission are compared to each other quantitatively. The modelling and performance evaluation technique is exemplified for the example of a Local Area Network. Numerical Results are reported which show the influence of some system and protocol parameters on the delay. The generality of the suggested approach allows the application to Wide Area Networks, as well.

A new inhouse communication system is suggested, integrating circuit switched services with variable bandwidth and packet switched services with variable throughput rate. The concept is based on the existing subscriber lines for ISDN services, and extended by small LANs and new PBXes, which are interconnected through broad-band links. LANs, PBXes and broad-band links are appropriate for integrated circuit switching and packet switching. In the first part of this paper, integration principles within the PBX as well as implementation aspects are outlined. The second part compares performance results of several strategies to achieve the integration of both switching principles on a ring system and presents a pilot implementation.

Queuing networks are widely used for modeling computer and communications systems. In recent years, efficient algorithms have been developed for the stationary state analysis from which the performance can be evaluated in terms of throughput and average delays. In this paper, the method of first passage times is used to analyze time-dependent processes within Markovian queuing networks as busy periods and response (cycle) times. Closed-form expressions are derived for the cyclic queuing system with two service stations. Generalizations to more complex networks are finally discussed. The analysis of life-time processes leads to a much deeper insight in the behavior of queuing networks compared to the stationary state analysis allowing for individual customer delay distributions or distributions of periods of continuous or simultaneous service. The method of first passage times is of particular advantage for cases with higher degrees of dependence as, e.g., networks with state- dependent service rates, queue disciplines other than FIFO, or cycle paths with overtaking.

A local area network with a completely distributed control is considered, where the connected peripherals (terminals, host computers) communicate with each other through addressed messages via a common high speed carrier. The network consists of three main layers: peripherals, network access controllers (NAC), and the communication subsystem. The higher levels of the network protocols are implemented within the NAC or the connected peripherals. The communication subsystem consists of the common high speed carrier and the channel access modules (CAM). The communication subsystem operates under a new carrier-sense-multiple-access (CSMA) protocol with collision detection and conflict resolution by dynamically controlled send priorities. This protocol combines both advantages of pure contention protocols for low traffic and fixed/demand assignment protocols for heavy traffic and reveals specific advantages with respect to overload control.