KEYWORDS: Local area networks, Standards development, Computer simulations, Binary data, Performance modeling, Iterated function systems, Data transmission, Francium, System integration
An enhanced CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol to be used in the Medium Access Control (MAC) layer of the IEEE 802.11 standard for wireless local area networks (wireless LANs) is proposed in this work. In wireless LANs, the CSMA/CA protocol supports asynchronous data transfer, and adopts an
acknowledgement mechanism to confirm successful transmissions and a handshaking mechanism to reduce collisions. In both cases, a binary exponential backoff mechanism is used. The enhanced protocol improves the exponential backoff scheme by dynamically adjusting the contention window (CW) around the optimal value. Moreover, an analytical model based on the Markov chain is developed to analyze the system performance in terms of throughput and delay. Numerical
results are presented to show the effect of the proposed backoff mechanism.
KEYWORDS: Curium, Unattended ground sensors, Video, Multimedia, Data transmission, Computer simulations, Performance modeling, Data modeling, System integration, Data centers
The Data Over Cable Service Interface Specifications (DOCSIS) of the Multimedia Cable Network System (MCNS) organization intends to support IP traffics over HFC (hybrid fiber/coax) networks with significantly higher data rates than analog modems and Integrated Service Digital Network (ISDN) links. The availability of high speed-access enables the delivery of high quality audio, video and interactive services. To support quality-of-service (QoS) for such applications, it is important for HFC networks to provide effective medium access and traffic scheduling mechanisms. In this work, a novel scheduling mechanism and a new bandwidth allocation scheme are proposed to support multimedia traffic over DOCSIS (Data Over Cable System Interface Specification)-compliant cable networks. The primary goal of our research is to improve the transmission of real-time variable bit rate (VBR) traffic in terms of throughput and delay under DOCSIS. To support integrated services, we also consider the transmission of constant bit rate (CBR) traffic and non-real-time traffic in the simulation. To demonstrate the performance, we compare the result of the proposed scheme with that of a simple multiple priority scheme. It is shown via simulation that the proposed method provides a significant amount of improvement over existing QoS scheduling services in DOCSIS. Finally, a discrete-time Markov model is used to analyze the performance of the voice traffic over DOCSIS-supported cable networks.
A novel scheduling mechanism and a new bandwidth allocation scheme are proposed in this work to support multimedia traffic over DOCSIS (Data Over Cable System Interface Specification)-compliant cable networks. The primary goal of our research is to improve the transmission of real-time variable bit rate (VBR) traffic in terms of throughput and delay under the current DOCSIS specifications. To support integrated services, we also consider the transmission of constant bit rate (CBR) traffic and non-real-time traffic in simulation. To demonstrate the performance, we compare the result of the proposed scheme with that of a simple multiple priority scheme. It is shown via simulation that the proposed method provides a significant amount of improvement over existing DOCSIS QoS scheduling services.
The Data Over Cable Service Interface Specifications (DOCSIS) of the Multimedia Cable Network System (MCNS) organization intends to support IP traffics over HFC (hybrid fiber/coax) networks with significantly higher data rates than analog modems and Integrated Service Digital Network (ISDN) links. The availability of high speed-access enables the delivery of high quality audio, video and interactive services. To support quality-of-service (QoS) for such multimedia applications, it is important for HFC networks to provide effective medium access and traffic scheduling mechanisms. In this work, we consider an HFC network that has a shared upstream channel for transmissions from stations assigned with different service priorities to the headend. We first present a multilevel priority collision resolution scheme with adaptive contention window adjustment. The proposed collision resolution scheme separates and resolves collisions for different classes of critically delay-sensitive and best effort traffics, thereby, achieving the capability for preemptive priorities. To enhance the performance of the proposed scheme, we adopt a novel methodology in which the headend dynamically selects the optimal backoff window size according to the estimate of the number of contending stations for each priority class. A traffic scheduling policy with multiple priority queues is also employed in the headend to schedule data transmissions. This scheduling strategy is used to satisfy bandwidth requirements for higher priority traffics. Simulations are conducted by using OPNET. We present a set of simulation scenarios to demonstrate the performance efficiency of the proposed scheme.
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