1,720,984 research outputs found
Efficiency and fairness issues in multihop networks supporting a guaranteed bandwidth transport service
No full textThis paper deals with the feasibility of a Guaranteed Bandwidth Transport Service (GBTS) on Shuffle Multihop Networks (SMHNs); moreover. a simple Resource Allocation Protocol. allowing a high flexibility in bandwidth allocation, is proposed. A performance study is carried out to verify the response of the SMHNs to GB traffic. In particular, the path blocking probability is evaluated by means of an analytical model in the cases of balanced and unbalanced loads. A comparison with the performance of similar LAN/MAN structures, i.e. simple ring and ring with spatial reuse, is carried out. Finally, a methodology to manage the resources in order to make the grade of service independent of the physical location of the network nodes is proposed and its impact on the network performance is evaluated. Moreover, some considerations about its actual implementation are presented
Throughput analysis of multihop shufflenets in a hot spot traffic scenario: impact of routing strategies
No full textThis paper deals with the analysis of the throughput performance of Shuffle Multihop Networks under general traffic configurations and aims at investigating the impact of different classes of routing schemes. A hot-spot traffic scenario was considered, modeling the presence of a centralized network resource to which a quota of the internal traffic is directed or originated from. The analysis was carried out by varying the traffic unbalance degree, from a uniform traffic distribution to a completely unbalanced one (all the traffic is concentrated in the hot spot node). As for the routing algorithms, both minimum path length (fixed or adaptive) and unconstrained path length schemes are studied. Simple analytical expressions of the actual throughput limits were obtained for each class of routing algorithms. By comparing the upper bounds with simulation results, it is shown that there exists an increase in the tightness of the upper bound which can be directly correlated to an increase in the network size. The results obtained show that the throughput performance deteriorates for increasing unbalance of the network load. This worsening can be partially relieved by employing adaptive routing algorithms. These algorithms provide remarkable throughput improvements with respect to fixed routing schemes, but only in the case of moderate hot spot traffic quota. Moreover, results show that unconstrained path length routing schemes lead to the best performance provided that the maximum path length be bounded
A burst handling protocol in shared buffer multihop networks
No full textIn this paper, the performance of Shuffle Multihop Networks under bursty and non-bursty traffic are investigated. In particular, some shortcomings of these architectures, in terms of throughput and fairness performance are highlighted. Moreover, a burst handling protocol is proposed that allows the network performance to be improved. The proposed mechanism is based on an enhanced node architecture. A preemptive traffic handling discipline is defined aiming at avoiding the loss of packets having already exploited network links and the transmission of corrupted bursts. The effectiveness of the proposed mechanism is finally proved by means of a thorough simulation analysis
Shuffle vs. Kautz/De Brujin logical topologies for multihop networks: a throughput comparison
No full textThis paper deals with the analysis of the throughput performance of various logical topologies for Multihop Networks. In particular, Shuffle Nets, De Bruijn graphs and Kautz graphs are analyzed. For the comparison, routing algorithms adopting minimum path length are considered. A hot-spot traffic scenario is adopted, modeling the presence of a centralized network resource to which a quota of the internal traffic is directed or originated from. The analysis is carried out by varying the traffic unbalance degree, from a uniform traffic distribution to a completely unbalanced one (all the traffic is concentrated in the hot-spot node). For ShuffleNets, simple analytical expressions of the actual throughput limits are utilized. In the case of De Bruijn and Kautz graphs, instead, a lower bound of the throughput is utilized, which coincides with the actual throughput in a wide range of values of the network size. The results obtained show that Shuffle and Kautz graphs always outperform De Bruijn topologies. Moreover, Shuffle Nets present a further advantage on the other topologies; in fact, since the nodes are topologically equivalent, the placement of the hot-spot node does not affect the throughput performance
Buffer sizing of a CRMA/ATM InterWorking Unit adopting a loss free access scheme
No full textOne of the main concerns in the interconnection of high speed lANs and ATM based networks is to avoid cell loss in the InterWorking Unit. In fact. in such environment, the retransmissions caused by the higher layers protocols can cause serious congestion problems. As a case study, the interconnection of a Gbit/s CRMA LAN through an ATM-based WAN is here considered. An Integrated Flow and Access Control (IFAC) protocol is proposed which exploiting the characteristics of the CRMA access scheme regulates the emission of cells towards the CRMA/ATM InterWorking Unit so that its buffer resources are not saturated. The emission of the ATM stations is controlled via a backpressure mechanism. The capacity of the InterWorking Unit buffer is virtually increased by utilizing the network latency as well as the station buffers. The protocol effectiveness has been validated through a simulation analysis. On the basis of the obtained results a study on the IWU buffer dimensioning has been carried out. In particular. the minimum buffer needed to can)' a given load has been determined. Moreover, some criteria have been given to properly fix the capacity to be allocated through the ATM interface
ANALYSIS OF ON-OFF SOURCE SHAPING FOR ATM MULTIPLEXING
No full textThis paper deals with the multiplexing of shaped ON-OFF sources on an ATM link. In particular, a (N)-Level Shaper is analyzed. It modulates the source output bit rate on the basis of the buffer occupancy level. A very accurate analytical model describing its behaviour is provided. Such a model allows an accurate description of the shaper output flow characteristics. A simple analytical model is also proposed for an ATM multiplexer in order to evaluate the advantages arising from the source shaping. The accuracy of the analytical results comes out from the comparison with the simulation ones. Numerical results show the effectiveness of the proposed shaping mechanism. They demonstrate that a substantial increase of the number of multiplexable sources is possible, for a given value of cell loss probability
On the design of a high performance ATM Metropolitan Area Network
No full textIn this paper some aspects concerning the design of high performance ATM compatible MANs are discussed. In particular, throughput and fairness parameters are focused. As far as fairness is concerned, a merit figure is here proposed and an evaluation procedure is presented. A general approach to cope with the above mentioned aspects is discussed and. as a proposed solution. a MAC protocol, called Adaptive Cycle Cell Insertion (ACCI), is described. The results of a performance evaluation study of the ACCI protocol are compared with those relevant to the current version of the IEEE standard 802.6
Analysis of Two Level Shaping for Multiplexing of ON-OFF ATM Sources
No full textThis paper deals with the analysis of the multiplexing of shaped ON-OFF sources in an ATM environment. In particular. a Two Level Shaper, modulating the source output bit rate on the basis of the buffer occupancy level, is studied. A very accurate analytical model describing its behaviour is provided too. Such a model allows an accurate description of the shaper output flow. To evaluate the advantages coming from the shaper introduction an approximate analytical model of an ATM multiplexer, based on the fluid model, is also proposed. The accuracy of the analytical results has been largely investigated by means of a simulation approach. Numerical results show the effectiveness of the proposed shaping mechanism, in terms of number of multiplexed sources. Moreover. the criteria for the choice of the shaper parameters are established and discussed
Guaranteed bandwidth transport service in multihop networks
No full textThis paper deals with the feasibility of a Guaranteed Bandwidth Transport Service (GBTS), usually employed for the handling of isochronous and/or data services with real time requirements, on Multihop Networks (MHNs). A Resource Allocation Protocol (RAP) for the set-up of GB calls is proposed. This protocol allows the low cost requirements of a LAN/MAN node to be satisfied, together with a high flexibility in bandwidth allocation. In the paper a performance study is carried out to verify the response of the MHNs to GB traffic. In particular, the path blocking probability has been evaluated by means of an analytical model in the cases of balanced and unbalanced loads. Moreover, a comparison with the performance of similar LAN/MAN structures, i.e. simple ring and ring with spatial reuse is carried out. Finally, a methodology to manage the resources in order to make the grade of service independent of the physical location of the network nodes is proposed and its impact on the network performance is evaluated
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