In order to efficiently utilize the scarce wireless resource as well as keep up with the ever-increasing demand for Quality-of-Service (QoS) of multimedia applications, wireless networks are undergoing rapid development and dramatic changes in the underlying technologies and protocols. The Medium Access Control (MAC) protocol, which coordinates the channel access and data transmission of wireless stations, plays a pivotal role in wireless networks. Performance modelling and analysis has been and continues to be of great theoretical and practical importance in the design and development of wireless networks. This research is devoted to developing efficient and cost-effective analytical tools for the performance analysis and enhancement of MAC protocols in Wireless Local Area Networks (WLANs) under heterogeneous multimedia traffic. To support the MAC-layer QoS in WLANs, the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol has proposed three QoS differentiation schemes in terms of Arbitrary Inter-Frame Space (AIFS), Contention Window (CW), and Transmission Opportunity (TXOP). This research starts with the development of new analytical models for the TXOP scheme specified in the EDCA protocol under Poisson traffic. A dynamic TXOP scheme is then proposed to adjust the TXOP limits according to the status of the transmission queue. Theoretical analysis and simulation experiments show that the proposed dynamic scheme largely improves the performance of TXOP. To evaluate the TXOP scheme in the presence of ii heterogeneous traffic, a versatile analytical model is developed to capture the traffic heterogeneity and model the features of burst transmission. The performance results highlight the importance of taking into account the heterogeneous traffic for the accurate evaluation of the TXOP scheme in wireless multimedia networks. To obtain a thorough and deep understanding of the performance attributes of the EDCA protocol, a comprehensive analytical model is then proposed to accommodate the integration of the three QoS schemes of EDCA in terms of AIFS, CW, and TXOP under Poisson traffic. The performance results show that the TXOP scheme can not only support service differentiation but also improve the network performance, whereas the AIFS and CW schemes provide QoS differentiation only. Moreover, the results demonstrate that the MAC buffer size has considerable impact on the QoS performance of EDCA under Poisson traffic. To investigate the performance of EDCA in wireless multimedia networks, an analytical model is further developed for EDCA under heterogeneous traffic. The performance results demonstrate the significant effects of heterogeneous traffic on the total delay and frame losses of EDCA with different buffer sizes. Finally, an efficient admission control scheme is presented for the IEEE 802.11e WLANs based on analytical modelling and a game-theoretical approach. The admission control scheme can maintain the system operation at an optimal point where the utility of the Access Point (AP) is maximized with the QoS constraints of various users.

In order to efficiently utilize the scarce wireless resource as well as keep up with the ever-increasing demand for Quality-of-Service (QoS) of multimedia applications, wireless networks are undergoing rapid development and dramatic changes in the underlying technologies and protocols. The Medium Access Control (MAC) protocol, which coordinates the channel access and data transmission of wireless stations, plays a pivotal role in wireless networks. Performance modelling and analysis has been and continues to be of great theoretical and practical importance in the design and development of wireless networks. This research is devoted to developing efficient and cost-effective analytical tools for the performance analysis and enhancement of MAC protocols in Wireless Local Area Networks (WLANs) under heterogeneous multimedia traffic. To support the MAC-layer QoS in WLANs, the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol has proposed three QoS differentiation schemes in terms of Arbitrary Inter-Frame Space (AIFS), Contention Window (CW), and Transmission Opportunity (TXOP). This research starts with the development of new analytical models for the TXOP scheme specified in the EDCA protocol under Poisson traffic. A dynamic TXOP scheme is then proposed to adjust the TXOP limits according to the status of the transmission queue. Theoretical analysis and simulation experiments show that the proposed dynamic scheme largely improves the performance of TXOP. To evaluate the TXOP scheme in the presence of ii heterogeneous traffic, a versatile analytical model is developed to capture the traffic heterogeneity and model the features of burst transmission. The performance results highlight the importance of taking into account the heterogeneous traffic for the accurate evaluation of the TXOP scheme in wireless multimedia networks. To obtain a thorough and deep understanding of the performance attributes of the EDCA protocol, a comprehensive analytical model is then proposed to accommodate the integration of the three QoS schemes of EDCA in terms of AIFS, CW, and TXOP under Poisson traffic. The performance results show that the TXOP scheme can not only support service differentiation but also improve the network performance, whereas the AIFS and CW schemes provide QoS differentiation only. Moreover, the results demonstrate that the MAC buffer size has considerable impact on the QoS performance of EDCA under Poisson traffic. To investigate the performance of EDCA in wireless multimedia networks, an analytical model is further developed for EDCA under heterogeneous traffic. The performance results demonstrate the significant effects of heterogeneous traffic on the total delay and frame losses of EDCA with different buffer sizes. Finally, an efficient admission control scheme is presented for the IEEE 802.11e WLANs based on analytical modelling and a game-theoretical approach. The admission control scheme can maintain the system operation at an optimal point where the utility of the Access Point (AP) is maximized with the QoS constraints of various users.

"A distributed queueing Medium Access Control (MAC) protocol is used in Distributed Queue Dual Bus (DQDB) networks. A modified version of the MAC protocol was proposed by R.R. Pillai and U. Mukherji in an attempt to overcome some of the shortcomings of the DQDB MAC protocol. They analyzed the performance of the system for Bernoulli arrivals and for large propagation delays between the nodes. We extend the performance analysis of the modified MAC protocol for a DQDB type of Network. The parameter of interest to us is the bus access delay. This has two components, viz., the request bus access delay and the data bu6 access delay. We use the model at the request point at node and present methods to evaluate the delay experienced in such a model. The model is an n-priority ./D/l queue with D vacations (non-preemptive priority) where n is the number of nodes sending requests on the request bus for transmission on the data bus. The methods presented help to evaluate the request bus access delay when the arrivals at each node are Markovian Arrival Processes (MAPs). The algorithms for evaluating the mean request bus access delay are based on matrix geometric techniques. Thus, one can use the algorithms developed in the literature to solve for the finite buffers case too. This model, for the request bus access delay, holds irrespective of the propagation delay between the nodes. We also evaluate the inter-departure time of class 1 customers and virtual customers in a 2-priority M/G/l system with G vacations (non-preemptive priority). In the case of Poisson arrivals at all the nodes, we would have a 2-priority M/D/l system with D vacations (non-preemptive priority). We thus evaluate the inter-arrival time of the free slots on the data bus as seen by Node 2. Note that this is independent of the number of active nodes in the network We then develop methods to evaluate the mean data bus access delay experienced by the customers at Node 2 in a three-node network with 2 nodes communicating with the third when the propagation delay between the nodes is large. We consider the case of finite Local Queue buffers at the two nodes. Using this assumption we arrive at process of arrivals to the Combined Queue and the process of free slots on the data bus to be Markov Modulated Bernoulli processes. The model at the combined queue at Node 2 then has a Quasi Birth-Death evolution. Thus, this system is solved by using the Ramaswami-Latouche algorithm. The stationary probabilities are then used to evaluate the mean data bus access delay experienced at Node 2. The finite buffer case of this system can be solved by G.Wi Stewart's algorithm. The method in modelling the system and the results are presented in detail for Poisson arrivals. The extension of this to more complex processes is also explained. We encounter in the analysis an explosion of the state-space of the system. We try to counter this by considering approximations to the process of free slots on the data bus. The approximations considered are on the basis of what are known as Idealized Aggregates. The performance of the approximation is also detailed. It works very well under low and moderate load but underestimates the mean delay under heavy load. Thereafter, we discuss the performance of the system with reference to the mean of the access delay and the standard deviation of the access delay under varying traffic at the two nodes. For this part we use simulation results to discuss the performance. The comparison between the performance measures at both the nodes is also done. Then we develop methods/techniques to understand the performance of the system when we have finite propagation delays between the nodes. We concentrate on the 3-node problem and calculate performance bounds based on linear programs. This is illustrated in detail for Bernoulli arrivals for the case of 1 slot propagation delay between the nodes as well as for the case of 2 slots propagation delay. The performance of the bounds obtained is also detailed. The presence of an idling system at the combined queue of Node 2 makes the bounds somewhat loose. Finally, we discuss the performance of the system with reference to the mean access delay and the standard deviation of the access delay under varying load on the system. Again, we rely on simulation studies. Finally, we study the performance of the system as a multiplexer. For this, we re­strict the traffic to Markov Modulated Processes (or those which would satisfy the Gartner-Ellis Theorem requirements). The traffic is characterized by what are known as Envelope Processes - Lower and Upper. The class of processes which satisfy the conditions of the Gartner-Ellis theorem come under the category where both the Envelope Processes exist and the Minimum Envelope Rate and the Maximum Lower Envelope Rate are the same. We use the system evolution equations at the combined queue at any node to develop re­lations between the various input and output processes. First, this is done for a. system of this kind, in isolation. Then, we consider this system as a part of the modified protocol and present relations, among the various input and output processes, which are specific to the modified protocol. The possible use of all of the above to do Admission Control at the entry point to the Asynchronous Transfer Mode (ATM) network is also presented.