Rising the level of abstraction in system modelling allows early verification of the system functionality, reducing the risk of long redesign cycles. Moving to a new flow introducing systemC as SDL allows the reuse of...
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Rising the level of abstraction in system modelling allows early verification of the system functionality, reducing the risk of long redesign cycles. Moving to a new flow introducing systemC as SDL allows the reuse of existing high-level C-models. A framework is presented that allows C-model integration and the connection of modules located at different levels of abstraction without the need to implement the communication or introduce adaptors to translate between the abstraction levels. the focus of the approach lies on high acceptance by the designers coming from a C and HDL based top-down design methodology.
We study the delay performance of policed traffic to provide real-time guarantees over wireless networks. A number of models have been presented in the literature to describe wireless (radio or optical) networks in te...
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We study the delay performance of policed traffic to provide real-time guarantees over wireless networks. A number of models have been presented in the literature to describe wireless (radio or optical) networks in terms of the wireless channel and the underlying error control mechanisms. We describe a general framework to incorporate such models into delay guarantee computations for real-time traffic. Static-priority scheduling is considered, and two different admission control mechanisms are used to achieve the trade-off between resource utilization and admission overhead.
the impact of bridge scheduling on the performance of two Bluetooth piconets with a MS-type bridge is analyzed. We consider bridge scheduling both with and without the precomputed schedule of rendezvous points, and de...
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the impact of bridge scheduling on the performance of two Bluetooth piconets with a MS-type bridge is analyzed. We consider bridge scheduling both with and without the precomputed schedule of rendezvous points, and derive the probability distribution for the bridge-master exchange time, as well as for the access delay and end-to-end delay for both intra and interpiconet traffic. We also discuss the stability limits under both bridge scheduling policies.
Sensors are typically deployed to gather data about the physical world and its artifacts for a variety of purposes that range from environment monitoring, control, to data analysis. Since sensors are resource constrai...
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Sensors are typically deployed to gather data about the physical world and its artifacts for a variety of purposes that range from environment monitoring, control, to data analysis. Since sensors are resource constrained, often sensor data is collected into a sensor database that resides at (more powerful) servers. A natural tradeoff exists between the sensor resources (bandwidth, energy) consumed and the quality of data collected at the server. Blindly transmitting sensor updates at a fixed periodicity to the server results in a suboptimal solution due to the differences in stability of sensor values and due to the varying application needs that impose different quality requirements across sensors. We propose adaptive data collection mechanisms for sensor environments that adjusts to these variations while at the same time optimizing the energy consumption of sensors. Our experimental results show significant energy savings compared to the naive approach to data collection.
We present a novel and complementary mechanism, called link-indexed statistical traffic predictor (LISP) to improve IEEE 802.11 power saving mechanism (PSM). LISP employs a simple, light-weight traffic prediction mech...
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We present a novel and complementary mechanism, called link-indexed statistical traffic predictor (LISP) to improve IEEE 802.11 power saving mechanism (PSM). LISP employs a simple, light-weight traffic prediction mechanism and enables each node to seek the inherent correlation between *** and incoming traffic. thereby nodes en route can stay awake in the BI in which a packet is anticipated to arrive, thus bridging a "freeway" for the packet to rapidly traverse the route. Meanwhile, the number of duty cycles is minimized and more energy is conserved. We conduct analytical and simulation studies and demonstrate the effectiveness of LISP.
We study backoff-based priority schemes for IEEE 802.11 and the emerging IEEE 802.11e standard by differentiating the minimum backoff window size, the backoff window-increasing factor, and the retransmission limit. An...
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We study backoff-based priority schemes for IEEE 802.11 and the emerging IEEE 802.11e standard by differentiating the minimum backoff window size, the backoff window-increasing factor, and the retransmission limit. An analytical model is proposed to derive saturation throughputs, saturation delays, and frame dropping probabilities of different priority classes for all proposed priority schemes. Simulations are conducted to validate analytical results. the proposed priority schemes can be easily implemented, and results are beneficial in designing good priority parameters.
Distributed denial of service (DDoS) attacks are currently major threats to communication in the Internet. A secure overlay services (SOS) architecture has been proposed to provide reliable communication between clien...
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Distributed denial of service (DDoS) attacks are currently major threats to communication in the Internet. A secure overlay services (SOS) architecture has been proposed to provide reliable communication between clients and a target under DDoS attacks. the SOS architecture employs a set of overlay nodes arranged in three hierarchical layers that controls access to the target. Although the architecture is novel and works well under simple congestion based attacks, we observe that it is vulnerable under more intelligent attacks. We generalize the SOS architecture by introducing more flexibility in layering to the original architecture. We define two intelligent DDoS attack models and develop an analytical approach to study the impacts of the number of layers, number of neighbors per node and the node distribution per layer on the system performance under these two attack models. Our data clearly demonstrate that performance is indeed sensitive to the design features and the different design features interact with each other to impact overall system performance.
Equation-based congestion control has been a promising alternative to TCP for real-time multimedia streaming over the Internet. However, its behavior remains unknown in the mobile ad hoc wireless network (MANET) domai...
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Equation-based congestion control has been a promising alternative to TCP for real-time multimedia streaming over the Internet. However, its behavior remains unknown in the mobile ad hoc wireless network (MANET) domain. We study the behavior of TFRC (TCP Friendly Rate control (S. Floyd et al., 2000; M. Handley et al., 2003) over a wide range of MANET scenarios, in terms of throughput fairness and smoothness. Our result shows that while TFRC is able to maintain throughput smoothness in MANET, it obtains less throughput than the competing TCP flows (i.e., being conservative). We analyze several factors contributing to TFRC's conservative behavior in MANET, many of which are inherent to the MANET network. We also show that TFRC's conservative behavior cannot be completely corrected by tuning its loss event interval estimator. Our study shows the limitations of applying TFRC to the MANET domain, and reveals some fundamental difficulties in doing so.
In unstructured peer-to-peer (P2P) systems, the mechanism of a peer randomly joining and leaving a P2P network causes topology mismatching between the P2P logical overlay network and the physical underlying network, c...
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In unstructured peer-to-peer (P2P) systems, the mechanism of a peer randomly joining and leaving a P2P network causes topology mismatching between the P2P logical overlay network and the physical underlying network, causing a large volume of redundant traffic in the Internet. In order to alleviate the mismatching problem, we propose adaptive connection establishment (ACE), an algorithm of building an overlay multicast tree among each source node and the peers within a certain diameter from the source peer, and further optimizing the neighbor connections that are not on the tree, while retaining the search scope. Our simulation study shows that this approach can effectively solve the mismatching problem and significantly reduce P2P traffic. We further study the tradeoffs between the topology optimization rate and the information exchange overhead by changing the diameter used to build the tree.
In access-point based wireless networks employing the IEEE 802.11 protocol in DCF mode, without bandwidth management and rate control, users pump data into the network as fast as it is generated. this results in a los...
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In access-point based wireless networks employing the IEEE 802.11 protocol in DCF mode, without bandwidth management and rate control, users pump data into the network as fast as it is generated. this results in a loss of QoS for the user and performance degradation of the network. there is a need for bandwidth allocation and for users to cooperatively controltheir rates based on the allocated bandwidth. We use price as a signal for bandwidth allocation in wireless hot spot networks. We allocate more bandwidth to users that pay more. At the same time, we also aim to maximize channel utilization and increase mean satisfaction across all the users.
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