SIP (Session Initiation Protocol) has been widely adopted as a signaling protocol to establish, modify and terminate multimedia sessions between end-users in the Internet. SIP introduces a retransmission mechanism to ...
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ISBN:
(纸本)9781617387036
SIP (Session Initiation Protocol) has been widely adopted as a signaling protocol to establish, modify and terminate multimedia sessions between end-users in the Internet. SIP introduces a retransmission mechanism to ensure the reliability of its real-time message delivery. However, retransmission makes server overload worse, as indicated by the recent server crashes in the real carrier networks. In this paper, we use a discrete time model to describe the queuing dynamics of an overloaded SIP server with the retransmission mechanism. We then derive a sufficient stability condition that a SIP server can handle the overload effectively under the retransmission mechanism. Discrete time model allows us to run fluid-based Matlab simulation directly to evaluate the overload performance. This approach is much simpler than event-driven simulation. Event-driven OPNET simulation was also conducted to observe the transient behaviour of an overloaded server in a SIP network. Our simulation results demonstrate that: (1) The sufficient stability bound is quite tight. The bound indicates that effective CPU utilization as low as 20% can still lead to an unstable system after a short period of demand burst or a temporary server slowdown. Resource overprovisioning is not a viable solution to the server crash problem;(2) By satisfying the stability condition, the initial queue size introduced by a transient overload can avoid a system crash. Such stability condition can help the operator to determine whether and when to activate overload control mechanism in case of heavy load.
Density evolution is often used to determine the performance of an ensemble of low-density parity-check (LDPC) codes under iterative message-passing algorithms. Conventional density evolution techniques over memoryles...
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ISBN:
(纸本)9781424463725
Density evolution is often used to determine the performance of an ensemble of low-density parity-check (LDPC) codes under iterative message-passing algorithms. Conventional density evolution techniques over memoryless channels are based on the independence assumption amongst all the processed messages in variable and check nodes. This assumption is valid for many algorithms such as standard belief propagation (BP) and min-sum (MS) algorithms. However, there are other important iterative algorithms such as successive relaxation (SR) versions of BP and MS, and differential decoding with binary message passing (DD-BMP) algorithm of Mobini et. al., for which this assumption is not valid. The dependence created among messages for these algorithms is due to the introduction of memory in the iterative algorithm. In this work, we propose a model for iterative decoding algorithms with memory which covers SR and DD-BMP algorithms as special cases. Based on this model, we derive a Bayesian network for iterative algorithms with memory over memoryless channels and use this representation to analyze the algorithms using density evolution. The density evolution technique is developed based on truncating the memory of the decoding process and approximating it with a finite order Markov process, and can be implemented efficiently. As an example, we apply our technique to analyze the performance of DD-BMP on regular LDPC code ensembles, and make a number of interesting observations with regard to the performance/complexity trade off of DD-BMP in comparison with BP and MS algorithms.
Random wandering is among the most frequently implemented mobile robotic behaviours. This paper presents a bio-inspired controller for mobile robots that generates deterministic wandering behaviour. Some results from ...
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ISBN:
(纸本)9783902661876
Random wandering is among the most frequently implemented mobile robotic behaviours. This paper presents a bio-inspired controller for mobile robots that generates deterministic wandering behaviour. Some results from the controller are derived theoretically and tested through simulations for symmetric cases, when analytic solutions are available. A technique to deal with non closed form wandering trajectories is also presented in a simple case study application.
Language identification is the task of identifying the language a given document is written in. This paper describes a detailed examination of what models perform best under different conditions, based on experiments ...
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The process of introducing emotion can be improved through three-dimensional (3D) tutoring system. The problem that still not solved is how to provide realistic tutor (avatar) in virtual environment. This paper propos...
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The process of introducing emotion can be improved through three-dimensional (3D) tutoring system. The problem that still not solved is how to provide realistic tutor (avatar) in virtual environment. This paper propose an approach to teach children on understanding emotion sensation through facial expression and sense of touch (haptic).The algorithm is created by calculating constant factor (f) based on maximum value of RGB and magnitude force then magnitude force range will be associated into particular colour. The Integration process will be started from rendering the facial expression then followed by adjusting the vibration power to emotion value. The result that achieved on experiment, it show around 71% students agree with the classification of magnitude force into emotion representation. Respondents commented that high magnitude force create similar sensation when respondents feel anger, while low magnitude force is more relaxing to respondents. Respondents also said that haptic and facial expression is very interactive and realistic.
In this paper, we propose an experiment design and implementation for distance evaluation in wireless sensor networks (WSN). More specifically, a WSN application is implemented for collecting received signal strength ...
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The widening performance gap between processor and disk demands innovations. Several optimization techniques, (e.g., read caching, write buffering, prefetching), have been proposed to narrow this gap. Read caching is ...
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ISBN:
(纸本)9780889868205
The widening performance gap between processor and disk demands innovations. Several optimization techniques, (e.g., read caching, write buffering, prefetching), have been proposed to narrow this gap. Read caching is the least effective technique among them in resource-poor condition. In this paper, we propose a novel technique which splits the disk cache into metadata and data to improve read miss ratio. The proposal is based on observations that metadata is smaller in size and more frequently accessed than its data. Split caches can reduce the interference between metadata and data. Our study shows that by splitting the disk cache the effective read miss ratio can be improved by 20%, which in turn would bring about 16% performance improvements in response time. Furthermore, the total size of the split caches is about 35%-97% of the unified cache to reach the same read miss ratio.
this paper presents an approach which integrates two formal verification techniques, model checking and the Event-B method in a way that makes it possible to benefit from the advantages of both methods in the design f...
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We explore the task of automatically classifying dialogue acts in 1-on-1 online chat forums, an increasingly popular means of providing customer service. In particular, we investigate the effectiveness of various feat...
Code Dissemination of a sensor network is useful for uploading a new code or for changing the functionality of the existing code. Code Dissemination may be done multiple times during a node's lifetime and therefor...
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