1,720,964 research outputs found
TCP performance in the GPRS system adopting the channel quality aware scheduler
No full textThe General Packet Radio Service (GPRS) networks are already implemented by several companies in different countries, however some problems related to the Quality of Service (QoS) observed by user and the efficient use of radio resources are not yet adequately addressed. In this framework, we propose a scheduling algorithm implemented at MAC layer, named as Channel Quality Aware Scheduler (CQAS). The main feature of the CQAS is that the user to serve is established taking into account the estimated channel quality for each of the active traffic flows. The performance of the proposed algorithm are evaluated in terms of goodput experimented by TCP clients, considering a set of concurrent rile transfers and independent time varying channels. The comparisons between the CQAS performance and those obtained using a simple Work Conserving Round Robin (WCRR) algorithm, highlight the improvements introduced by the proposed algorithm. Moreover, the analysis emphasizes that the appropriate choice of both the channel Coding Scheme (CS) and the scheduling algorithm is needed in order to increase the radio resource utilization
Admission region for multimedia services in IEEE 802.11e systems
No full textThe paper presents the simulation analysis aimed at evaluating the admission region of a IEEE 802.11 e draft 4.0 standard, adopting the EDCF (Enhanced Distributed Coordination Function) access control mechanism. In particular, the study gives an estimate of the number of QoS aware services, namely videoconference and Voice over IP (VoIP), that can be admitted to the transport service offered by the EDCF, while their QoS requirements are satisfied. In the study, the ideal radio channel model is assumed. Furthermore, the traffic sources are obtained from traffic data acquired by means of measurement campaigns made during emulation of VoIP and videoconference services, based respectively on G.723.1 and H.261 codec. Finally the QoS parameters experienced by a mix of VoIP, videoconference and TCP traffic transmitted according to the EDCF mechanism are compared with those obtained when the DCF mechanism is adopted. The result of this comparison clearly highlights the efficiency in the traffic differentiation of the EDCF mechanism
A comparison of HTB based channel-aware schedulers for 802.11 systems
No full textThe 802.11 commercial devices adopt a simple FIFO scheduler, which does not allow to isolate flows addressed to different destinations. This characteristic leads to the well-known performance anomaly of 802.11: when one or more STAs experiment poor radio channel conditions, they increase the time spent to transmit a single packet leading to an inefficient use of the shared medium. These phenomena have as a consequence the worsening of the performance of all the STAs sharing the wireless medium independently of their radio channel conditions. In this scenario, the paper proposes an architecture for a scheduling algorithm to implement in the AP for the downlink traffic, based on Hierarchical Token Bucket (HTB). The peculiarity of the proposed architecture is its ability to take into account, besides the transport service class required by the destination user, the channel quality experimented by the destination mobile STAtion (STA). Starting from this architecture two scheduling schemes are then proposed: the Wireless HTB (WHTB) and the Time-based WHTB (TWHTB). Both schemes are implemented in a prototype of AP. Hence, the performance of the proposed scheduling algorithms are experimentally evaluated and compared with those obtained with standard scheduling algorithm, which do not take into account information on channel quality. Finally, the paper presents a comparison in terms of implementation issues highlighted by the two proposed schemes, during the developing phase and the experimental analysis
On synchronization techniques: performance and impact on time metrics monitoring
No full textThe paper presents an experimental comparison of device synchronization strategies to monitor quality of service (QoS) time metrics, such as the one-way delay and the delay variation. The compared strategies are based on global positioning system (GPS), public Internet network time protocol (NTP) servers and ad hoc GPS-based NTP servers with different treatments of the NTP traffic. The presented experimental results allow to quantitatively evaluate the level of performance achievable using each synchronization technique. Finally, considering a satellite test bed, we focus our analysis on two relevant aspects of time metrics monitoring: the impact of the synchronization errors on the metrics observation and the different values that can be measured when a metric is monitored at the application or data link level. Copyright (C) 2003 John Wiley Sons, Ltd
An Experience in IPv6 Networking supporting Ecumene Web Information System for Cultural Heritage
No full textPeople interested in Cultural Heritage constitute a community of users characterized by a high degree of mobility. Users visiting cultural sites hosted by local institutions expect to access information pertaining to cultural/artistic heritage from anywhere at anytime, as they can through the desk at their own homes or offices. The Ecumene Web Information System, developed in the groundwork of the Ecumene Project, offers a framework for accessing the artistic and cultural information through a Web application. In this paper, we expose the underlying communication network architecture, based on the IPv6 protocol and investigate the benefits of its adoption, in terms of mobility and security support. Indeed, the need of granting different access rights to different user classes enforces the security requirements of the system. Lastly, the open issues related to the practical integration of an experimental testbed with Mobile IPv6 and IPSec support are detailed and possible solutions are presented
On chaotic prediction and application to resource allocation strategies
No full textThe fractal nature of Internet traffic allows extending the application of the nonlinear chaotic system theory to the traffic control in modern telecommunication networks. In particular, the prediction techniques developed for these systems provide teletraffic engineers with a novel powerful tool for designing optimized traffic control algorithms. In this framework, the paper presents the performance evaluation of the Radial Basis Function Predictor (RBFP) in predicting actual traffic data. Predictor parameters are selected automatically by minimizing a suitably defined metric of prediction accuracy. The prediction system is then exploited in a simple resource allocation strategy to test the performance improvement achievable whenever a prediction of the future traffic intensity is available. The results obtained by means of discrete event simulation using actual traffic data are encouraging and stimulate a further-investigation of this approach
MIPSD (Mobility-oriented IPSec Daemon): a Tool for Integrated Mobility and Security Support in the Ecumene Network
No full textThe IP protocol is stateless and connectionless, hence cannot guarantee a secure delivery of the information. IPSec offers stateful security introducing logical connections between couples of peers. The management of these IPSec Security Associations is often delegated to dynamic protocols, such as ISAKMP and IKE, because of the obvious scalability problem of a manual configuration approach. However, the address of each peer must be known in advance to the other one in order for the ISAKMP exchange to be completed successfully. This assumption cannot be always guaranteed, especially when mobility is taken into consideration. In such cases, a proper mechanism to retrieve the correspondent peer IPv6 address must be taken into account. The demo consists of an overview of the functionalities of the Ecumene Web Information System, developed in the groundwork of the Ecumene Project, focusing mainly on the enhancements developed (in the form of the MIPSD daemon) to allow automatic IPSec SA insaturation between hosts which wants to access the network and the appropriate Site Gateway
The Wireless Hierarchical Token Bucket: a Channel Aware Scheduler for 802.11 Networks
No full textThe paper proposes air architecture for a scheduling algorithm, to be integrated in IEEE 802.11 Access Points (AP), able to take into account, besides the transport service class required by the destination user, the channel quality experimented by the destination mobile STAtion (STA). The relevance of this topic is due to the observation that when one or more STAs experiment poor radio channel conditions, they increase the time spent to transmit a single packet, due to the retransmission of corrupted frames and the adoption of a transmission techniques at lower bit rate, leading to an inefficient use of the shared medium. These phenomena have as a consequence the worsening of the performance of all the STAs sharing the wireless medium independently of their radio channel conditions. The adoption of a scheduling algorithm able to manage information on channel quality permits to reduce these effects, not penalizing the STAs experimenting good channel condition and, as a consequence, their experimented throughput. As a result, only the STAs in bad channel conditions experiment a reduction of throughput. A prototype of an AP equipment implementing the proposed architecture is then presented; it has been obtained modifying the Hierarchical Token Bucket (HTB) and has been indicated as Wireless Hierarchical Token Bucket (WHTB). The performance of the presented prototype are experimentally evaluated and compared with those obtained with standard scheduling algorithm, which do not take into account information on channel quality
Automatic IPSec Security Association Negotiation in Mobile-Oriented IPv6 Networks
No full textIntegrated mobility and security support is one of the most desirable feature for a network. Although IPv6 offers protocol which satisfies both these requirements, practical issues still exist which do not allow for a really integrated environment. Our contribution towards such integration is the development of a solution to automate the task of setting up the appropriate IPSec Security Associations each time a node connects to an IPv6 subnet. The result is mipsd, a user-space daemon which interacts with the IKE daemon running at the mobile host to allow the completely automated setup of SA towards the corresponding Security Gateway
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